Table of Contents
List of Examples
lib.versions.splitVersion
usage examplelib.versions.major
usage examplelib.versions.minor
usage examplelib.versions.patch
usage examplelib.versions.majorMinor
usage examplelib.versions.pad
usage examplelib.options.isOption
usage examplelib.options.mkOption
usage examplelib.options.mkEnableOption
usage examplelib.options.mkPackageOption
usage examplelib.options.getValues
usage examplelib.options.getFiles
usage examplelib.options.showOption
usage examplelib.path.append
usage examplelib.path.hasPrefix
usage examplelib.path.removePrefix
usage examplelib.path.splitRoot
usage examplelib.path.hasStorePathPrefix
usage examplelib.path.subpath.isValid
usage examplelib.path.subpath.join
usage examplelib.path.subpath.components
usage examplelib.path.subpath.normalise
usage examplelib.sources.commitIdFromGitRepo
usage examplelib.sources.cleanSource
usage examplelib.sources.cleanSourceWith
usage examplelib.sources.sourceByRegex
usage examplelib.sources.sourceFilesBySuffices
usage examplepkgs
callPackage
from a scopepassthru
attributesfetchurl
to download a filefetchurl
to download a file with multiple possible URLsfetchurl
fetchzip
to output contents directlyfetchzip
to decompress a .rar
filerunCommandWith
runCommand
makeDesktopItem
makeDesktopItem
writeTextFile
writeTextFile
writeTextFile
writeText
writeTextDir
writeScript
writeScriptBin
writeShellScript
writeShellScriptBin
pkg-config
modules are exposed using default valuespkg-config
modules are exposed using explicit module namesnix
documentationtesters.shellcheck
runNixOSTest
fakeNss
with dockerTools.buildImage
fakeNss
with an override to add extra linespostExtract
runAsRoot
extraCommands
streamLayeredImage
config
dockerTools.pullImage
dockerTools.exportImage
dockerTools.exportImage
in DockerdockerTools.exportImage
dockerTools.exportImage
with a path as fromImage
dockerTools
’s environment helpers with buildImage
dockerTools
’s environment helpers with buildLayeredImage
dockerTools.shadowSetup
with dockerTools.buildImage
dockerTools.shadowSetup
with dockerTools.buildLayeredImage
buildNixShellImage
with the build environment for the hello
packagestreamNixShellImage
with the build environment for the hello
packagestreamNixShellImage
shellHook
to a Docker image built with streamNixShellImage
bash
mkBinaryCache
javaPackages
with nix repl
pkgs.zlib.override {}
pkgs.buildEmscriptenPackage {}
pkgs.linuxPackages_custom
with a specific source, version, and config filemellanox
driverspkgs.substitute
pkgs.substituteAll
pkgs.substituteAllFiles
Table of Contents
The Nix Packages collection (Nixpkgs) is a set of thousands of packages for the Nix package manager, released under a permissive MIT license. Packages are available for several platforms, and can be used with the Nix package manager on most GNU/Linux distributions as well as NixOS.
This document is the user reference manual for Nixpkgs. It describes entire public interface of Nixpkgs in a concise and orderly manner, and all relevant behaviors, with examples and cross-references.
To discover other kinds of documentation:
nix.dev: Tutorials and guides for getting things done with Nix
NixOS Option Search and reference documentation
NixOS manual: Reference documentation for the NixOS Linux distribution
CONTRIBUTING.md
: Contributing to Nixpkgs, including this manual
Nix expressions describe how to build packages from source and are collected in the nixpkgs repository. Also included in the collection are Nix expressions for NixOS modules. With these expressions the Nix package manager can build binary packages.
Packages, including the Nix packages collection, are distributed through
channels. The collection is
distributed for users of Nix on non-NixOS distributions through the channel
nixpkgs-unstable
. Users of NixOS generally use one of the nixos-*
channels,
e.g. nixos-22.11
, which includes all packages and modules for the stable NixOS
22.11. Stable NixOS releases are generally only given
security updates. More up to date packages and modules are available via the
nixos-unstable
channel.
Both nixos-unstable
and nixpkgs-unstable
follow the master
branch of the
nixpkgs repository, although both do lag the master
branch by generally
a couple of days. Updates to a channel are
distributed as soon as all tests for that channel pass, e.g.
this table
shows the status of tests for the nixpkgs-unstable
channel.
The tests are conducted by a cluster called Hydra,
which also builds binary packages from the Nix expressions in Nixpkgs for
x86_64-linux
, i686-linux
and x86_64-darwin
.
The binaries are made available via a binary cache.
The current Nix expressions of the channels are available in the
nixpkgs repository in branches
that correspond to the channel names (e.g. nixos-22.11-small
).
Table of Contents
Packages receive varying degrees of support, both in terms of maintainer attention and available computation resources for continuous integration (CI).
Below is the list of the best supported platforms:
x86_64-linux
: Highest level of support.
aarch64-linux
: Well supported, with most packages building successfully in CI.
aarch64-darwin
: Receives better support than x86_64-darwin
.
x86_64-darwin
: Receives some support.
There are many other platforms with varying levels of support. The provisional platform list in Appendix A of RFC046, while not up to date, can be used as guidance.
A more formal definition of the platform support tiers is provided in RFC046, but has not been fully implemented yet.
Table of Contents
Nix comes with certain defaults about which packages can and cannot be installed, based on a package’s metadata. By default, Nix will prevent installation if any of the following criteria are true:
The package is thought to be broken, and has had its meta.broken
set to true
.
The package isn’t intended to run on the given system, as none of its meta.platforms
match the given system.
The package’s meta.license
is set to a license which is considered to be unfree.
The package has known security vulnerabilities but has not or can not be updated for some reason, and a list of issues has been entered in to the package’s meta.knownVulnerabilities
.
Each of these criteria can be altered in the Nixpkgs configuration.
All this is checked during evaluation already, and the check includes any package that is evaluated. In particular, all build-time dependencies are checked.
A user’s Nixpkgs configuration is stored in a user-specific configuration file located at ~/.config/nixpkgs/config.nix
. For example:
{
allowUnfree = true;
}
Unfree software is not tested or built in Nixpkgs continuous integration, and therefore not cached. Most unfree licenses prohibit either executing or distributing the software.
There are two ways to try compiling a package which has been marked as broken.
For allowing the build of a broken package once, you can use an environment variable for a single invocation of the nix tools:
$ export NIXPKGS_ALLOW_BROKEN=1
For permanently allowing broken packages to be built, you may add allowBroken = true;
to your user’s configuration file, like this:
{
allowBroken = true;
}
There are also two ways to try compiling a package which has been marked as unsupported for the given system.
For allowing the build of an unsupported package once, you can use an environment variable for a single invocation of the nix tools:
$ export NIXPKGS_ALLOW_UNSUPPORTED_SYSTEM=1
For permanently allowing unsupported packages to be built, you may add allowUnsupportedSystem = true;
to your user’s configuration file, like this:
{
allowUnsupportedSystem = true;
}
The difference between a package being unsupported on some system and being broken is admittedly a bit fuzzy. If a program ought to work on a certain platform, but doesn’t, the platform should be included in meta.platforms
, but marked as broken with e.g. meta.broken = !hostPlatform.isWindows
. Of course, this begs the question of what “ought” means exactly. That is left to the package maintainer.
All users of Nixpkgs are free software users, and many users (and developers) of Nixpkgs want to limit and tightly control their exposure to unfree software. At the same time, many users need (or want) to run some specific pieces of proprietary software. Nixpkgs includes some expressions for unfree software packages. By default unfree software cannot be installed and doesn’t show up in searches.
There are several ways to tweak how Nix handles a package which has been marked as unfree.
To temporarily allow all unfree packages, you can use an environment variable for a single invocation of the nix tools:
$ export NIXPKGS_ALLOW_UNFREE=1
It is possible to permanently allow individual unfree packages, while still blocking unfree packages by default using the allowUnfreePredicate
configuration option in the user configuration file.
This option is a function which accepts a package as a parameter, and returns a boolean. The following example configuration accepts a package and always returns false:
{
allowUnfreePredicate = (pkg: false);
}
For a more useful example, try the following. This configuration only allows unfree packages named roon-server and visual studio code:
{
allowUnfreePredicate = pkg: builtins.elem (lib.getName pkg) [
"roon-server"
"vscode"
];
}
It is also possible to allow and block licenses that are specifically acceptable or not acceptable, using allowlistedLicenses
and blocklistedLicenses
, respectively.
The following example configuration allowlists the licenses amd
and wtfpl
:
{
allowlistedLicenses = with lib.licenses; [ amd wtfpl ];
}
The following example configuration blocklists the gpl3Only
and agpl3Only
licenses:
{
blocklistedLicenses = with lib.licenses; [ agpl3Only gpl3Only ];
}
Note that allowlistedLicenses
only applies to unfree licenses unless allowUnfree
is enabled. It is not a generic allowlist for all types of licenses. blocklistedLicenses
applies to all licenses.
A complete list of licenses can be found in the file lib/licenses.nix
of the nixpkgs tree.
There are several ways to tweak how Nix handles a package which has been marked as insecure.
To temporarily allow all insecure packages, you can use an environment variable for a single invocation of the nix tools:
$ export NIXPKGS_ALLOW_INSECURE=1
It is possible to permanently allow individual insecure packages, while still blocking other insecure packages by default using the permittedInsecurePackages
configuration option in the user configuration file.
The following example configuration permits the installation of the hypothetically insecure package hello
, version 1.2.3
:
{
permittedInsecurePackages = [
"hello-1.2.3"
];
}
It is also possible to create a custom policy around which insecure packages to allow and deny, by overriding the allowInsecurePredicate
configuration option.
The allowInsecurePredicate
option is a function which accepts a package and returns a boolean, much like allowUnfreePredicate
.
The following configuration example only allows insecure packages with very short names:
{
allowInsecurePredicate = pkg: builtins.stringLength (lib.getName pkg) <= 5;
}
Note that permittedInsecurePackages
is only checked if allowInsecurePredicate
is not specified.
packageOverrides
You can define a function called packageOverrides
in your local ~/.config/nixpkgs/config.nix
to override Nix packages. It must be a function that takes pkgs as an argument and returns a modified set of packages.
{
packageOverrides = pkgs: rec {
foo = pkgs.foo.override { /* ... */ };
};
}
config
Options Reference The following attributes can be passed in config
.
enableParallelBuildingByDefault
Whether to set enableParallelBuilding
to true by default while building nixpkgs packages.
Changing the default may cause a mass rebuild.
Type: boolean
Default:
false
Declared by:
pkgs/top-level/config.nix
|
allowAliases
Whether to expose old attribute names for compatibility.
The recommended setting is to enable this, as it improves backward compatibility, easing updates.
The only reason to disable aliases is for continuous integration purposes. For instance, Nixpkgs should not depend on aliases in its internal code. Projects that aren’t Nixpkgs should be cautious of instantly removing all usages of aliases, as migrating too soon can break compatibility with the stable Nixpkgs releases.
Type: boolean
Default:
true
Declared by:
pkgs/top-level/config.nix
|
allowBroken
Whether to allow broken packages.
See Installing broken packages in the NixOS manual.
Type: boolean
Default:
false || builtins.getEnv "NIXPKGS_ALLOW_BROKEN" == "1"
Declared by:
pkgs/top-level/config.nix
|
allowUnfree
Whether to allow unfree packages.
See Installing unfree packages in the NixOS manual.
Type: boolean
Default:
false || builtins.getEnv "NIXPKGS_ALLOW_UNFREE" == "1"
Declared by:
pkgs/top-level/config.nix
|
allowUnsupportedSystem
Whether to allow unsupported packages.
See Installing packages on unsupported systems in the NixOS manual.
Type: boolean
Default:
false || builtins.getEnv "NIXPKGS_ALLOW_UNSUPPORTED_SYSTEM" == "1"
Declared by:
pkgs/top-level/config.nix
|
checkMeta
Whether to check that the meta
attribute of derivations are correct during evaluation time.
Type: boolean
Default:
false
Declared by:
pkgs/top-level/config.nix
|
configurePlatformsByDefault
Whether to set configurePlatforms
to ["build" "host"]
by default while building nixpkgs packages.
Changing the default may cause a mass rebuild.
Type: boolean
Default:
false
Declared by:
pkgs/top-level/config.nix
|
contentAddressedByDefault
Whether to set __contentAddressed
to true by default while building nixpkgs packages.
Changing the default may cause a mass rebuild.
Type: boolean
Default:
false
Declared by:
pkgs/top-level/config.nix
|
cudaSupport
Whether to build packages with CUDA support by default while building nixpkgs packages. Changing the default may cause a mass rebuild.
Type: boolean
Default:
false
Declared by:
pkgs/top-level/config.nix
|
doCheckByDefault
Whether to run checkPhase
by default while building nixpkgs packages.
Changing the default may cause a mass rebuild.
Type: boolean
Default:
false
Declared by:
pkgs/top-level/config.nix
|
replaceBootstrapFiles
Use the bootstrap files returned instead of the default bootstrap files. The default bootstrap files are passed as an argument. Changing the default may cause a mass rebuild.
Type: function that evaluates to a(n) attribute set of package
Default:
lib.id
Example:
prevFiles:
let
replacements = {
"sha256-YQlr088HPoVWBU2jpPhpIMyOyoEDZYDw1y60SGGbUM0=" = import <nix/fetchurl.nix> {
url = "(custom glibc linux x86_64 bootstrap-tools.tar.xz)";
hash = "(...)";
};
"sha256-QrTEnQTBM1Y/qV9odq8irZkQSD9uOMbs2Q5NgCvKCNQ=" = import <nix/fetchurl.nix> {
url = "(custom glibc linux x86_64 busybox)";
hash = "(...)";
executable = true;
};
};
in
builtins.mapAttrs (name: prev: replacements.${prev.outputHash} or prev) prevFiles
Declared by:
pkgs/top-level/config.nix
|
rocmSupport
Whether to build packages with ROCm support by default while building nixpkgs packages. Changing the default may cause a mass rebuild.
Type: boolean
Default:
false
Declared by:
pkgs/top-level/config.nix
|
showDerivationWarnings
Which warnings to display for potentially dangerous
or deprecated values passed into stdenv.mkDerivation
.
A list of warnings can be found in /pkgs/stdenv/generic/check-meta.nix.
This is not a stable interface; warnings may be added, changed or removed without prior notice.
Type: list of value “maintainerless” (singular enum)
Default:
[ ]
Declared by:
pkgs/top-level/config.nix
|
strictDepsByDefault
Whether to set strictDeps
to true by default while building nixpkgs packages.
Changing the default may cause a mass rebuild.
Type: boolean
Default:
false
Declared by:
pkgs/top-level/config.nix
|
structuredAttrsByDefault
Whether to set __structuredAttrs
to true by default while building nixpkgs packages.
Changing the default may cause a mass rebuild.
Type: boolean
Default:
false
Declared by:
pkgs/top-level/config.nix
|
warnUndeclaredOptions
Whether to warn when config
contains an unrecognized attribute.
Type: boolean
Default:
false
Declared by:
pkgs/top-level/config.nix
|
Using packageOverrides
, it is possible to manage packages declaratively. This means that we can list all of our desired packages within a declarative Nix expression. For example, to have aspell
, bc
, ffmpeg
, coreutils
, gdb
, nixUnstable
, emscripten
, jq
, nox
, and silver-searcher
, we could use the following in ~/.config/nixpkgs/config.nix
:
{
packageOverrides = pkgs: with pkgs; {
myPackages = pkgs.buildEnv {
name = "my-packages";
paths = [
aspell
bc
coreutils
gdb
ffmpeg
nixUnstable
emscripten
jq
nox
silver-searcher
];
};
};
}
To install it into our environment, you can just run nix-env -iA nixpkgs.myPackages
. If you want to load the packages to be built from a working copy of nixpkgs
you just run nix-env -f. -iA myPackages
. To explore what’s been installed, just look through ~/.nix-profile/
. You can see that a lot of stuff has been installed. Some of this stuff is useful some of it isn’t. Let’s tell Nixpkgs to only link the stuff that we want:
{
packageOverrides = pkgs: with pkgs; {
myPackages = pkgs.buildEnv {
name = "my-packages";
paths = [
aspell
bc
coreutils
gdb
ffmpeg
nixUnstable
emscripten
jq
nox
silver-searcher
];
pathsToLink = [ "/share" "/bin" ];
};
};
}
pathsToLink
tells Nixpkgs to only link the paths listed which gets rid of the extra stuff in the profile. /bin
and /share
are good defaults for a user environment, getting rid of the clutter. If you are running on Nix on MacOS, you may want to add another path as well, /Applications
, that makes GUI apps available.
After building that new environment, look through ~/.nix-profile
to make sure everything is there that we wanted. Discerning readers will note that some files are missing. Look inside ~/.nix-profile/share/man/man1/
to verify this. There are no man pages for any of the Nix tools! This is because some packages like Nix have multiple outputs for things like documentation (see section 4). Let’s make Nix install those as well.
{
packageOverrides = pkgs: with pkgs; {
myPackages = pkgs.buildEnv {
name = "my-packages";
paths = [
aspell
bc
coreutils
ffmpeg
nixUnstable
emscripten
jq
nox
silver-searcher
];
pathsToLink = [ "/share/man" "/share/doc" "/bin" ];
extraOutputsToInstall = [ "man" "doc" ];
};
};
}
This provides us with some useful documentation for using our packages. However, if we actually want those manpages to be detected by man, we need to set up our environment. This can also be managed within Nix expressions.
{
packageOverrides = pkgs: with pkgs; rec {
myProfile = writeText "my-profile" ''
export PATH=$HOME/.nix-profile/bin:/nix/var/nix/profiles/default/bin:/sbin:/bin:/usr/sbin:/usr/bin
export MANPATH=$HOME/.nix-profile/share/man:/nix/var/nix/profiles/default/share/man:/usr/share/man
'';
myPackages = pkgs.buildEnv {
name = "my-packages";
paths = [
(runCommand "profile" {} ''
mkdir -p $out/etc/profile.d
cp ${myProfile} $out/etc/profile.d/my-profile.sh
'')
aspell
bc
coreutils
ffmpeg
man
nixUnstable
emscripten
jq
nox
silver-searcher
];
pathsToLink = [ "/share/man" "/share/doc" "/bin" "/etc" ];
extraOutputsToInstall = [ "man" "doc" ];
};
};
}
For this to work fully, you must also have this script sourced when you are logged in. Try adding something like this to your ~/.profile
file:
#!/bin/sh
if [ -d "${HOME}/.nix-profile/etc/profile.d" ]; then
for i in "${HOME}/.nix-profile/etc/profile.d/"*.sh; do
if [ -r "$i" ]; then
. "$i"
fi
done
fi
Now just run . "${HOME}/.profile"
and you can start loading man pages from your environment.
Configuring GNU info is a little bit trickier than man pages. To work correctly, info needs a database to be generated. This can be done with some small modifications to our environment scripts.
{
packageOverrides = pkgs: with pkgs; rec {
myProfile = writeText "my-profile" ''
export PATH=$HOME/.nix-profile/bin:/nix/var/nix/profiles/default/bin:/sbin:/bin:/usr/sbin:/usr/bin
export MANPATH=$HOME/.nix-profile/share/man:/nix/var/nix/profiles/default/share/man:/usr/share/man
export INFOPATH=$HOME/.nix-profile/share/info:/nix/var/nix/profiles/default/share/info:/usr/share/info
'';
myPackages = pkgs.buildEnv {
name = "my-packages";
paths = [
(runCommand "profile" {} ''
mkdir -p $out/etc/profile.d
cp ${myProfile} $out/etc/profile.d/my-profile.sh
'')
aspell
bc
coreutils
ffmpeg
man
nixUnstable
emscripten
jq
nox
silver-searcher
texinfoInteractive
];
pathsToLink = [ "/share/man" "/share/doc" "/share/info" "/bin" "/etc" ];
extraOutputsToInstall = [ "man" "doc" "info" ];
postBuild = ''
if [ -x $out/bin/install-info -a -w $out/share/info ]; then
shopt -s nullglob
for i in $out/share/info/*.info $out/share/info/*.info.gz; do
$out/bin/install-info $i $out/share/info/dir
done
fi
'';
};
};
}
postBuild
tells Nixpkgs to run a command after building the environment. In this case, install-info
adds the installed info pages to dir
which is GNU info’s default root node. Note that texinfoInteractive
is added to the environment to give the install-info
command.
Table of Contents
This chapter describes how to extend and change Nixpkgs using overlays. Overlays are used to add layers in the fixed-point used by Nixpkgs to compose the set of all packages.
Nixpkgs can be configured with a list of overlays, which are applied in order. This means that the order of the overlays can be significant if multiple layers override the same package.
The list of overlays can be set either explicitly in a Nix expression, or through <nixpkgs-overlays>
or user configuration files.
On a NixOS system the value of the nixpkgs.overlays
option, if present, is passed to the system Nixpkgs directly as an argument. Note that this does not affect the overlays for non-NixOS operations (e.g. nix-env
), which are looked up independently.
The list of overlays can be passed explicitly when importing nixpkgs, for example import <nixpkgs> { overlays = [ overlay1 overlay2 ]; }
.
NOTE: DO NOT USE THIS in nixpkgs. Further overlays can be added by calling the pkgs.extend
or pkgs.appendOverlays
, although it is often preferable to avoid these functions, because they recompute the Nixpkgs fixpoint, which is somewhat expensive to do.
The list of overlays is determined as follows.
First, if an overlays
argument to the Nixpkgs function itself is given, then that is used and no path lookup will be performed.
Otherwise, if the Nix path entry <nixpkgs-overlays>
exists, we look for overlays at that path, as described below.
See the section on NIX_PATH
in the Nix manual for more details on how to set a value for <nixpkgs-overlays>.
If one of ~/.config/nixpkgs/overlays.nix
and ~/.config/nixpkgs/overlays/
exists, then we look for overlays at that path, as described below. It is an error if both exist.
If we are looking for overlays at a path, then there are two cases:
If the path is a file, then the file is imported as a Nix expression and used as the list of overlays.
If the path is a directory, then we take the content of the directory, order it lexicographically, and attempt to interpret each as an overlay by:
Importing the file, if it is a .nix
file.
Importing a top-level default.nix
file, if it is a directory.
Because overlays that are set in NixOS configuration do not affect non-NixOS operations such as nix-env
, the overlays.nix
option provides a convenient way to use the same overlays for a NixOS system configuration and user configuration: the same file can be used as overlays.nix
and imported as the value of nixpkgs.overlays
.
Overlays are Nix functions which accept two arguments, conventionally called self
and super
, and return a set of packages. For example, the following is a valid overlay.
self: super:
{
boost = super.boost.override {
python = self.python3;
};
rr = super.callPackage ./pkgs/rr {
stdenv = self.stdenv_32bit;
};
}
The first argument (self
) corresponds to the final package set. You should use this set for the dependencies of all packages specified in your overlay. For example, all the dependencies of rr
in the example above come from self
, as well as the overridden dependencies used in the boost
override.
The second argument (super
) corresponds to the result of the evaluation of the previous stages of Nixpkgs. It does not contain any of the packages added by the current overlay, nor any of the following overlays. This set should be used either to refer to packages you wish to override, or to access functions defined in Nixpkgs. For example, the original recipe of boost
in the above example, comes from super
, as well as the callPackage
function.
The value returned by this function should be a set similar to pkgs/top-level/all-packages.nix
, containing overridden and/or new packages.
Overlays are similar to other methods for customizing Nixpkgs, in particular the packageOverrides
attribute described in the section called “Modify packages via packageOverrides
”. Indeed, packageOverrides
acts as an overlay with only the super
argument. It is therefore appropriate for basic use, but overlays are more powerful and easier to distribute.
Certain software packages have different implementations of the same interface. Other distributions have functionality to switch between these. For example, Debian provides DebianAlternatives. Nixpkgs has what we call alternatives
, which are configured through overlays.
In Nixpkgs, we have multiple implementations of the BLAS/LAPACK numerical linear algebra interfaces. They are:
The Nixpkgs attribute is openblas
for ILP64 (integer width = 64 bits) and openblasCompat
for LP64 (integer width = 32 bits). openblasCompat
is the default.
LAPACK reference (also provides BLAS and CBLAS)
The Nixpkgs attribute is lapack-reference
.
Intel MKL (only works on the x86_64 architecture, unfree)
The Nixpkgs attribute is mkl
.
BLIS, available through the attribute blis
, is a framework for linear algebra kernels. In addition, it implements the BLAS interface.
AMD BLIS/LIBFLAME (optimized for modern AMD x86_64 CPUs)
The AMD fork of the BLIS library, with attribute amd-blis
, extends BLIS with optimizations for modern AMD CPUs. The changes are usually submitted to the upstream BLIS project after some time. However, AMD BLIS typically provides some performance improvements on AMD Zen CPUs. The complementary AMD LIBFLAME library, with attribute amd-libflame
, provides a LAPACK implementation.
Introduced in PR #83888, we are able to override the blas
and lapack
packages to use different implementations, through the blasProvider
and lapackProvider
argument. This can be used to select a different provider. BLAS providers will have symlinks in $out/lib/libblas.so.3
and $out/lib/libcblas.so.3
to their respective BLAS libraries. Likewise, LAPACK providers will have symlinks in $out/lib/liblapack.so.3
and $out/lib/liblapacke.so.3
to their respective LAPACK libraries. For example, Intel MKL is both a BLAS and LAPACK provider. An overlay can be created to use Intel MKL that looks like:
self: super:
{
blas = super.blas.override {
blasProvider = self.mkl;
};
lapack = super.lapack.override {
lapackProvider = self.mkl;
};
}
This overlay uses Intel’s MKL library for both BLAS and LAPACK interfaces. Note that the same can be accomplished at runtime using LD_LIBRARY_PATH
of libblas.so.3
and liblapack.so.3
. For instance:
$ LD_LIBRARY_PATH=$(nix-build -A mkl)/lib${LD_LIBRARY_PATH:+:}$LD_LIBRARY_PATH nix-shell -p octave --run octave
Intel MKL requires an openmp
implementation when running with multiple processors. By default, mkl
will use Intel’s iomp
implementation if no other is specified, but this is a runtime-only dependency and binary compatible with the LLVM implementation. To use that one instead, Intel recommends users set it with LD_PRELOAD
. Note that mkl
is only available on x86_64-linux
and x86_64-darwin
. Moreover, Hydra is not building and distributing pre-compiled binaries using it.
To override blas
and lapack
with its reference implementations (i.e. for development purposes), one can use the following overlay:
self: super:
{
blas = super.blas.override {
blasProvider = self.lapack-reference;
};
lapack = super.lapack.override {
lapackProvider = self.lapack-reference;
};
}
For BLAS/LAPACK switching to work correctly, all packages must depend on blas
or lapack
. This ensures that only one BLAS/LAPACK library is used at one time. There are two versions of BLAS/LAPACK currently in the wild, LP64
(integer size = 32 bits) and ILP64
(integer size = 64 bits). The attributes blas
and lapack
are LP64
by default. Their ILP64
version are provided through the attributes blas-ilp64
and lapack-ilp64
. Some software needs special flags or patches to work with ILP64
. You can check if ILP64
is used in Nixpkgs with blas.isILP64
and lapack.isILP64
. Some software does NOT work with ILP64
, and derivations need to specify an assertion to prevent this. You can prevent ILP64
from being used with the following:
{ stdenv, blas, lapack, ... }:
assert (!blas.isILP64) && (!lapack.isILP64);
stdenv.mkDerivation {
# ...
}
All programs that are built with MPI support use the generic attribute mpi
as an input. At the moment Nixpkgs natively provides two different MPI implementations:
To provide MPI enabled applications that use MPICH
, instead of the default Open MPI
, use the following overlay:
self: super:
{
mpi = self.mpich;
}
Table of Contents
Sometimes one wants to override parts of nixpkgs
, e.g. derivation attributes, the results of derivations.
These functions are used to make changes to packages, returning only single packages. Overlays, on the other hand, can be used to combine the overridden packages across the entire package set of Nixpkgs.
The function override
is usually available for all the derivations in the nixpkgs expression (pkgs
).
It is used to override the arguments passed to a function.
Example usages:
pkgs.foo.override { arg1 = val1; arg2 = val2; /* ... */ }
It’s also possible to access the previous arguments.
pkgs.foo.override (previous: { arg1 = previous.arg1; /* ... */ })
import pkgs.path { overlays = [ (self: super: {
foo = super.foo.override { barSupport = true ; };
})];}
{
mypkg = pkgs.callPackage ./mypkg.nix {
mydep = pkgs.mydep.override { /* ... */ };
};
}
In the first example, pkgs.foo
is the result of a function call with some default arguments, usually a derivation. Using pkgs.foo.override
will call the same function with the given new arguments.
Many packages, like the foo
example above, provide package options with default values in their arguments, to facilitate overriding.
Because it’s not usually feasible to test that packages build with all combinations of options, you might find that a package doesn’t build if you override options to non-default values.
Package maintainers are not expected to fix arbitrary combinations of options. If you find that something doesn’t work, please submit a fix, ideally with a regression test. If you want to ensure that things keep working, consider becoming a maintainer for the package.
The function overrideAttrs
allows overriding the attribute set passed to a stdenv.mkDerivation
call, producing a new derivation based on the original one. This function is available on all derivations produced by the stdenv.mkDerivation
function, which is most packages in the nixpkgs expression pkgs
.
Example usages:
{
helloBar = pkgs.hello.overrideAttrs (finalAttrs: previousAttrs: {
pname = previousAttrs.pname + "-bar";
});
}
In the above example, “-bar” is appended to the pname attribute, while all other attributes will be retained from the original hello
package.
The argument previousAttrs
is conventionally used to refer to the attr set originally passed to stdenv.mkDerivation
.
The argument finalAttrs
refers to the final attributes passed to mkDerivation
, plus the finalPackage
attribute which is equal to the result of mkDerivation
or subsequent overrideAttrs
calls.
If only a one-argument function is written, the argument has the meaning of previousAttrs
.
Function arguments can be omitted entirely if there is no need to access previousAttrs
or finalAttrs
.
{
helloWithDebug = pkgs.hello.overrideAttrs {
separateDebugInfo = true;
};
}
In the above example, the separateDebugInfo
attribute is overridden to be true, thus building debug info for helloWithDebug
.
Note that separateDebugInfo
is processed only by the stdenv.mkDerivation
function, not the generated, raw Nix derivation. Thus, using overrideDerivation
will not work in this case, as it overrides only the attributes of the final derivation. It is for this reason that overrideAttrs
should be preferred in (almost) all cases to overrideDerivation
, i.e. to allow using stdenv.mkDerivation
to process input arguments, as well as the fact that it is easier to use (you can use the same attribute names you see in your Nix code, instead of the ones generated (e.g. buildInputs
vs nativeBuildInputs
), and it involves less typing).
You should prefer overrideAttrs
in almost all cases, see its documentation for the reasons why. overrideDerivation
is not deprecated and will continue to work, but is less nice to use and does not have as many abilities as overrideAttrs
.
Do not use this function in Nixpkgs as it evaluates a derivation before modifying it, which breaks package abstraction. In addition, this evaluation-per-function application incurs a performance penalty, which can become a problem if many overrides are used. It is only intended for ad-hoc customisation, such as in ~/.config/nixpkgs/config.nix
.
The function overrideDerivation
creates a new derivation based on an existing one by overriding the original’s attributes with the attribute set produced by the specified function. This function is available on all derivations defined using the makeOverridable
function. Most standard derivation-producing functions, such as stdenv.mkDerivation
, are defined using this function, which means most packages in the nixpkgs expression, pkgs
, have this function.
Example usage:
{
mySed = pkgs.gnused.overrideDerivation (oldAttrs: {
name = "sed-4.2.2-pre";
src = fetchurl {
url = "ftp://alpha.gnu.org/gnu/sed/sed-4.2.2-pre.tar.bz2";
hash = "sha256-MxBJRcM2rYzQYwJ5XKxhXTQByvSg5jZc5cSHEZoB2IY=";
};
patches = [];
});
}
In the above example, the name
, src
, and patches
of the derivation will be overridden, while all other attributes will be retained from the original derivation.
The argument oldAttrs
is used to refer to the attribute set of the original derivation.
A package’s attributes are evaluated before being modified by the overrideDerivation
function. For example, the name
attribute reference in url = "mirror://gnu/hello/${name}.tar.gz";
is filled-in before the overrideDerivation
function modifies the attribute set. This means that overriding the name
attribute, in this example, will not change the value of the url
attribute. Instead, we need to override both the name
and url
attributes.
The function lib.makeOverridable
is used to make the result of a function easily customizable. This utility only makes sense for functions that accept an argument set and return an attribute set.
Example usage:
{
f = { a, b }: { result = a+b; };
c = lib.makeOverridable f { a = 1; b = 2; };
}
The variable c
is the value of the f
function applied with some default arguments. Hence the value of c.result
is 3
, in this example.
The variable c
however also has some additional functions, like
c.override which can be used to override the
default arguments. In this example the value of
(c.override { a = 4; }).result
is 6.
lib
Table of Contents
Table of Contents
The nixpkgs repository has several utility functions to manipulate Nix expressions.
Nixpkgs provides a standard library at pkgs.lib
, or through import <nixpkgs/lib>
.
lib.asserts.assertMsg
Throw if pred is false, else return pred. Intended to be used to augment asserts with helpful error messages.
pred
Predicate that needs to succeed, otherwise msg
is thrown
msg
Message to throw in case pred
fails
assertMsg :: Bool -> String -> Bool
lib.asserts.assertMsg
usage exampleassertMsg false "nope"
stderr> error: nope
assert assertMsg ("foo" == "bar") "foo is not bar, silly"; ""
stderr> error: foo is not bar, silly
Located at lib/asserts.nix:39 in <nixpkgs>
.
lib.asserts.assertOneOf
Specialized assertMsg
for checking if val
is one of the elements
of the list xs
. Useful for checking enums.
name
The name of the variable the user entered val
into, for inclusion in the error message
val
The value of what the user provided, to be compared against the values in xs
xs
The list of valid values
assertOneOf :: String -> ComparableVal -> List ComparableVal -> Bool
lib.asserts.assertOneOf
usage examplelet sslLibrary = "libressl";
in assertOneOf "sslLibrary" sslLibrary [ "openssl" "bearssl" ]
stderr> error: sslLibrary must be one of [
stderr> "openssl"
stderr> "bearssl"
stderr> ], but is: "libressl"
Located at lib/asserts.nix:83 in <nixpkgs>
.
lib.asserts.assertEachOneOf
Specialized assertMsg
for checking if every one of vals
is one of the elements
of the list xs
. Useful for checking lists of supported attributes.
name
The name of the variable the user entered val
into, for inclusion in the error message
vals
The list of values of what the user provided, to be compared against the values in xs
xs
The list of valid values
assertEachOneOf :: String -> List ComparableVal -> List ComparableVal -> Bool
lib.asserts.assertEachOneOf
usage examplelet sslLibraries = [ "libressl" "bearssl" ];
in assertEachOneOf "sslLibraries" sslLibraries [ "openssl" "bearssl" ]
stderr> error: each element in sslLibraries must be one of [
stderr> "openssl"
stderr> "bearssl"
stderr> ], but is: [
stderr> "libressl"
stderr> "bearssl"
stderr> ]
Located at lib/asserts.nix:135 in <nixpkgs>
.
Operations on attribute sets.
lib.attrsets.attrByPath
Return an attribute from nested attribute sets.
Nix has an attribute selection operator . or
which is sufficient for such queries, as long as the number of attributes is static. For example:
(x.a.b or 6) == attrByPath ["a" "b"] 6 x
# and
(x.${f p}."example.com" or 6) == attrByPath [ (f p) "example.com" ] 6 x
attrPath
A list of strings representing the attribute path to return from set
default
Default value if attrPath
does not resolve to an existing value
set
The nested attribute set to select values from
attrByPath :: [String] -> Any -> AttrSet -> Any
lib.attrsets.attrByPath
usage examplex = { a = { b = 3; }; }
# ["a" "b"] is equivalent to x.a.b
# 6 is a default value to return if the path does not exist in attrset
attrByPath ["a" "b"] 6 x
=> 3
attrByPath ["z" "z"] 6 x
=> 6
Located at lib/attrsets.nix:65 in <nixpkgs>
.
lib.attrsets.hasAttrByPath
Return if an attribute from nested attribute set exists.
Nix has a has attribute operator ?
, which is sufficient for such queries, as long as the number of attributes is static. For example:
(x?a.b) == hasAttrByPath ["a" "b"] x
# and
(x?${f p}."example.com") == hasAttrByPath [ (f p) "example.com" ] x
Laws:
hasAttrByPath [] x == true
attrPath
A list of strings representing the attribute path to check from set
e
The nested attribute set to check
hasAttrByPath :: [String] -> AttrSet -> Bool
lib.attrsets.hasAttrByPath
usage examplex = { a = { b = 3; }; }
hasAttrByPath ["a" "b"] x
=> true
hasAttrByPath ["z" "z"] x
=> false
hasAttrByPath [] (throw "no need")
=> true
Located at lib/attrsets.nix:133 in <nixpkgs>
.
lib.attrsets.longestValidPathPrefix
Return the longest prefix of an attribute path that refers to an existing attribute in a nesting of attribute sets.
Can be used after mapAttrsRecursiveCond
to apply a condition,
although this will evaluate the predicate function on sibling attributes as well.
Note that the empty attribute path is valid for all values, so this function only throws an exception if any of its inputs does.
Laws:
attrsets.longestValidPathPrefix [] x == []
hasAttrByPath (attrsets.longestValidPathPrefix p x) x == true
attrPath
A list of strings representing the longest possible path that may be returned.
v
The nested attribute set to check.
attrsets.longestValidPathPrefix :: [String] -> Value -> [String]
lib.attrsets.longestValidPathPrefix
usage examplex = { a = { b = 3; }; }
attrsets.longestValidPathPrefix ["a" "b" "c"] x
=> ["a" "b"]
attrsets.longestValidPathPrefix ["a"] x
=> ["a"]
attrsets.longestValidPathPrefix ["z" "z"] x
=> []
attrsets.longestValidPathPrefix ["z" "z"] (throw "no need")
=> []
Located at lib/attrsets.nix:202 in <nixpkgs>
.
lib.attrsets.setAttrByPath
Create a new attribute set with value
set at the nested attribute location specified in attrPath
.
attrPath
A list of strings representing the attribute path to set
value
The value to set at the location described by attrPath
setAttrByPath :: [String] -> Any -> AttrSet
lib.attrsets.setAttrByPath
usage examplesetAttrByPath ["a" "b"] 3
=> { a = { b = 3; }; }
Located at lib/attrsets.nix:265 in <nixpkgs>
.
lib.attrsets.getAttrFromPath
Like attrByPath
, but without a default value. If it doesn’t find the
path it will throw an error.
Nix has an attribute selection operator which is sufficient for such queries, as long as the number of attributes is static. For example:
x.a.b == getAttrByPath ["a" "b"] x
# and
x.${f p}."example.com" == getAttrByPath [ (f p) "example.com" ] x
attrPath
A list of strings representing the attribute path to get from set
set
The nested attribute set to find the value in.
getAttrFromPath :: [String] -> AttrSet -> Any
lib.attrsets.getAttrFromPath
usage examplex = { a = { b = 3; }; }
getAttrFromPath ["a" "b"] x
=> 3
getAttrFromPath ["z" "z"] x
=> error: cannot find attribute `z.z'
Located at lib/attrsets.nix:319 in <nixpkgs>
.
lib.attrsets.concatMapAttrs
Map each attribute in the given set and merge them into a new attribute set.
f
1. Function argument
v
2. Function argument
concatMapAttrs :: (String -> a -> AttrSet) -> AttrSet -> AttrSet
lib.attrsets.concatMapAttrs
usage exampleconcatMapAttrs
(name: value: {
${name} = value;
${name + value} = value;
})
{ x = "a"; y = "b"; }
=> { x = "a"; xa = "a"; y = "b"; yb = "b"; }
Located at lib/attrsets.nix:360 in <nixpkgs>
.
lib.attrsets.updateManyAttrsByPath
Update or set specific paths of an attribute set.
Takes a list of updates to apply and an attribute set to apply them to,
and returns the attribute set with the updates applied. Updates are
represented as { path = ...; update = ...; }
values, where path
is a
list of strings representing the attribute path that should be updated,
and update
is a function that takes the old value at that attribute path
as an argument and returns the new
value it should be.
Properties:
Updates to deeper attribute paths are applied before updates to more shallow attribute paths
Multiple updates to the same attribute path are applied in the order they appear in the update list
If any but the last path
element leads into a value that is not an
attribute set, an error is thrown
If there is an update for an attribute path that doesn’t exist, accessing the argument in the update function causes an error, but intermediate attribute sets are implicitly created as needed
updateManyAttrsByPath :: [{ path :: [String]; update :: (Any -> Any); }] -> AttrSet -> AttrSet
lib.attrsets.updateManyAttrsByPath
usage exampleupdateManyAttrsByPath [
{
path = [ "a" "b" ];
update = old: { d = old.c; };
}
{
path = [ "a" "b" "c" ];
update = old: old + 1;
}
{
path = [ "x" "y" ];
update = old: "xy";
}
] { a.b.c = 0; }
=> { a = { b = { d = 1; }; }; x = { y = "xy"; }; }
Located at lib/attrsets.nix:423 in <nixpkgs>
.
lib.attrsets.attrVals
Return the specified attributes from a set.
nameList
The list of attributes to fetch from set
. Each attribute name must exist on the attrbitue set
set
The set to get attribute values from
attrVals :: [String] -> AttrSet -> [Any]
lib.attrsets.attrVals
usage exampleattrVals ["a" "b" "c"] as
=> [as.a as.b as.c]
Located at lib/attrsets.nix:513 in <nixpkgs>
.
lib.attrsets.attrValues
Return the values of all attributes in the given set, sorted by attribute name.
attrValues :: AttrSet -> [Any]
lib.attrsets.attrValues
usage exampleattrValues {c = 3; a = 1; b = 2;}
=> [1 2 3]
Located at lib/attrsets.nix:539 in <nixpkgs>
.
lib.attrsets.getAttrs
Given a set of attribute names, return the set of the corresponding attributes from the given set.
names
A list of attribute names to get out of set
attrs
The set to get the named attributes from
getAttrs :: [String] -> AttrSet -> AttrSet
lib.attrsets.getAttrs
usage examplegetAttrs [ "a" "b" ] { a = 1; b = 2; c = 3; }
=> { a = 1; b = 2; }
Located at lib/attrsets.nix:574 in <nixpkgs>
.
lib.attrsets.catAttrs
Collect each attribute named attr
from a list of attribute
sets. Sets that don’t contain the named attribute are ignored.
attr
The attribute name to get out of the sets.
list
The list of attribute sets to go through
catAttrs :: String -> [AttrSet] -> [Any]
lib.attrsets.catAttrs
usage examplecatAttrs "a" [{a = 1;} {b = 0;} {a = 2;}]
=> [1 2]
Located at lib/attrsets.nix:609 in <nixpkgs>
.
lib.attrsets.filterAttrs
Filter an attribute set by removing all attributes for which the given predicate return false.
pred
Predicate taking an attribute name and an attribute value, which returns true
to include the attribute, or false
to exclude the attribute.
set
The attribute set to filter
filterAttrs :: (String -> Any -> Bool) -> AttrSet -> AttrSet
lib.attrsets.filterAttrs
usage examplefilterAttrs (n: v: n == "foo") { foo = 1; bar = 2; }
=> { foo = 1; }
Located at lib/attrsets.nix:644 in <nixpkgs>
.
lib.attrsets.filterAttrsRecursive
Filter an attribute set recursively by removing all attributes for which the given predicate return false.
pred
Predicate taking an attribute name and an attribute value, which returns true
to include the attribute, or false
to exclude the attribute.
set
The attribute set to filter
filterAttrsRecursive :: (String -> Any -> Bool) -> AttrSet -> AttrSet
lib.attrsets.filterAttrsRecursive
usage examplefilterAttrsRecursive (n: v: v != null) { foo = { bar = null; }; }
=> { foo = {}; }
Located at lib/attrsets.nix:682 in <nixpkgs>
.
lib.attrsets.foldlAttrs
Like lib.lists.foldl'
but for attribute sets.
Iterates over every name-value pair in the given attribute set.
The result of the callback function is often called acc
for accumulator. It is passed between callbacks from left to right and the final acc
is the return value of foldlAttrs
.
Attention:
There is a completely different function lib.foldAttrs
which has nothing to do with this function, despite the similar name.
f
1. Function argument
init
2. Function argument
set
3. Function argument
foldlAttrs :: ( a -> String -> b -> a ) -> a -> { ... :: b } -> a
lib.attrsets.foldlAttrs
usage examplefoldlAttrs
(acc: name: value: {
sum = acc.sum + value;
names = acc.names ++ [name];
})
{ sum = 0; names = []; }
{
foo = 1;
bar = 10;
}
->
{
sum = 11;
names = ["bar" "foo"];
}
foldlAttrs
(throw "function not needed")
123
{};
->
123
foldlAttrs
(acc: _: _: acc)
3
{ z = throw "value not needed"; a = throw "value not needed"; };
->
3
The accumulator doesn't have to be an attrset.
It can be as simple as a number or string.
foldlAttrs
(acc: _: v: acc * 10 + v)
1
{ z = 1; a = 2; };
->
121
Located at lib/attrsets.nix:776 in <nixpkgs>
.
lib.attrsets.foldAttrs
Apply fold functions to values grouped by key.
op
A function, given a value and a collector combines the two.
nul
The starting value.
list_of_attrs
A list of attribute sets to fold together by key.
foldAttrs :: (Any -> Any -> Any) -> Any -> [AttrSets] -> Any
lib.attrsets.foldAttrs
usage examplefoldAttrs (item: acc: [item] ++ acc) [] [{ a = 2; } { a = 3; }]
=> { a = [ 2 3 ]; }
Located at lib/attrsets.nix:817 in <nixpkgs>
.
lib.attrsets.collect
Recursively collect sets that verify a given predicate named pred
from the set attrs
. The recursion is stopped when the predicate is
verified.
pred
Given an attribute’s value, determine if recursion should stop.
attrs
The attribute set to recursively collect.
collect :: (AttrSet -> Bool) -> AttrSet -> [x]
lib.attrsets.collect
usage examplecollect isList { a = { b = ["b"]; }; c = [1]; }
=> [["b"] [1]]
collect (x: x ? outPath)
{ a = { outPath = "a/"; }; b = { outPath = "b/"; }; }
=> [{ outPath = "a/"; } { outPath = "b/"; }]
Located at lib/attrsets.nix:865 in <nixpkgs>
.
lib.attrsets.cartesianProduct
Return the cartesian product of attribute set value combinations.
attrsOfLists
Attribute set with attributes that are lists of values
cartesianProduct :: AttrSet -> [AttrSet]
lib.attrsets.cartesianProduct
usage examplecartesianProduct { a = [ 1 2 ]; b = [ 10 20 ]; }
=> [
{ a = 1; b = 10; }
{ a = 1; b = 20; }
{ a = 2; b = 10; }
{ a = 2; b = 20; }
]
Located at lib/attrsets.nix:907 in <nixpkgs>
.
lib.attrsets.mapCartesianProduct
Return the result of function f applied to the cartesian product of attribute set value combinations. Equivalent to using cartesianProduct followed by map.
f
A function, given an attribute set, it returns a new value.
attrsOfLists
Attribute set with attributes that are lists of values
mapCartesianProduct :: (AttrSet -> a) -> AttrSet -> [a]
lib.attrsets.mapCartesianProduct
usage examplemapCartesianProduct ({a, b}: "${a}-${b}") { a = [ "1" "2" ]; b = [ "3" "4" ]; }
=> [ "1-3" "1-4" "2-3" "2-4" ]
Located at lib/attrsets.nix:948 in <nixpkgs>
.
lib.attrsets.nameValuePair
Utility function that creates a {name, value}
pair as expected by builtins.listToAttrs
.
name
Attribute name
value
Attribute value
nameValuePair :: String -> Any -> { name :: String; value :: Any; }
lib.attrsets.nameValuePair
usage examplenameValuePair "some" 6
=> { name = "some"; value = 6; }
Located at lib/attrsets.nix:981 in <nixpkgs>
.
lib.attrsets.mapAttrs
Apply a function to each element in an attribute set, creating a new attribute set.
f
A function that takes an attribute name and its value, and returns the new value for the attribute.
attrset
The attribute set to iterate through.
mapAttrs :: (String -> Any -> Any) -> AttrSet -> AttrSet
lib.attrsets.mapAttrs
usage examplemapAttrs (name: value: name + "-" + value)
{ x = "foo"; y = "bar"; }
=> { x = "x-foo"; y = "y-bar"; }
Located at lib/attrsets.nix:1018 in <nixpkgs>
.
lib.attrsets.mapAttrs'
Like mapAttrs
, but allows the name of each attribute to be
changed in addition to the value. The applied function should
return both the new name and value as a nameValuePair
.
f
A function, given an attribute’s name and value, returns a new nameValuePair
.
set
Attribute set to map over.
mapAttrs' :: (String -> Any -> { name :: String; value :: Any; }) -> AttrSet -> AttrSet
lib.attrsets.mapAttrs'
usage examplemapAttrs' (name: value: nameValuePair ("foo_" + name) ("bar-" + value))
{ x = "a"; y = "b"; }
=> { foo_x = "bar-a"; foo_y = "bar-b"; }
Located at lib/attrsets.nix:1055 in <nixpkgs>
.
lib.attrsets.mapAttrsToList
Call a function for each attribute in the given set and return the result in a list.
f
A function, given an attribute’s name and value, returns a new value.
attrs
Attribute set to map over.
mapAttrsToList :: (String -> a -> b) -> AttrSet -> [b]
lib.attrsets.mapAttrsToList
usage examplemapAttrsToList (name: value: name + value)
{ x = "a"; y = "b"; }
=> [ "xa" "yb" ]
Located at lib/attrsets.nix:1093 in <nixpkgs>
.
lib.attrsets.attrsToList
Deconstruct an attrset to a list of name-value pairs as expected by builtins.listToAttrs
.
Each element of the resulting list is an attribute set with these attributes:
name
(string): The name of the attribute
value
(any): The value of the attribute
The following is always true:
builtins.listToAttrs (attrsToList attrs) == attrs
The opposite is not always true. In general expect that
attrsToList (builtins.listToAttrs list) != list
This is because the listToAttrs
removes duplicate names and doesn’t preserve the order of the list.
set
The attribute set to deconstruct.
attrsToList :: AttrSet -> [ { name :: String; value :: Any; } ]
lib.attrsets.attrsToList
usage exampleattrsToList { foo = 1; bar = "asdf"; }
=> [ { name = "bar"; value = "asdf"; } { name = "foo"; value = 1; } ]
Located at lib/attrsets.nix:1141 in <nixpkgs>
.
lib.attrsets.mapAttrsRecursive
Like mapAttrs
, except that it recursively applies itself to the leaf attributes of a potentially-nested attribute set:
the second argument of the function will never be an attrset.
Also, the first argument of the mapping function is a list of the attribute names that form the path to the leaf attribute.
For a function that gives you control over what counts as a leaf, see mapAttrsRecursiveCond
.
mapAttrsRecursive (path: value: concatStringsSep "-" (path ++ [value]))
{ n = { a = "A"; m = { b = "B"; c = "C"; }; }; d = "D"; }
evaluates to
{ n = { a = "n-a-A"; m = { b = "n-m-b-B"; c = "n-m-c-C"; }; }; d = "d-D"; }
mapAttrsRecursive :: ([String] -> a -> b) -> AttrSet -> AttrSet
Located at lib/attrsets.nix:1169 in <nixpkgs>
.
lib.attrsets.mapAttrsRecursiveCond
Like mapAttrsRecursive
, but it takes an additional predicate that tells it whether to recurse into an attribute set.
If the predicate returns false, mapAttrsRecursiveCond
does not recurse, but instead applies the mapping function.
If the predicate returns true, it does recurse, and does not apply the mapping function.
Map derivations to their name
attribute.
Derivatons are identified as attribute sets that contain { type = "derivation"; }
.
mapAttrsRecursiveCond
(as: !(as ? "type" && as.type == "derivation"))
(x: x.name)
attrs
mapAttrsRecursiveCond :: (AttrSet -> Bool) -> ([String] -> a -> b) -> AttrSet -> AttrSet
Located at lib/attrsets.nix:1198 in <nixpkgs>
.
lib.attrsets.genAttrs
Generate an attribute set by mapping a function over a list of attribute names.
names
Names of values in the resulting attribute set.
f
A function, given the name of the attribute, returns the attribute’s value.
genAttrs :: [ String ] -> (String -> Any) -> AttrSet
lib.attrsets.genAttrs
usage examplegenAttrs [ "foo" "bar" ] (name: "x_" + name)
=> { foo = "x_foo"; bar = "x_bar"; }
Located at lib/attrsets.nix:1245 in <nixpkgs>
.
lib.attrsets.isDerivation
Check whether the argument is a derivation. Any set with
{ type = "derivation"; }
counts as a derivation.
value
Value to check.
isDerivation :: Any -> Bool
lib.attrsets.isDerivation
usage examplenixpkgs = import <nixpkgs> {}
isDerivation nixpkgs.ruby
=> true
isDerivation "foobar"
=> false
Located at lib/attrsets.nix:1282 in <nixpkgs>
.
lib.attrsets.toDerivation
Converts a store path to a fake derivation.
path
A store path to convert to a derivation.
lib.attrsets.optionalAttrs
If cond
is true, return the attribute set as
,
otherwise an empty attribute set.
cond
Condition under which the as
attribute set is returned.
as
The attribute set to return if cond
is true
.
optionalAttrs :: Bool -> AttrSet -> AttrSet
lib.attrsets.optionalAttrs
usage exampleoptionalAttrs (true) { my = "set"; }
=> { my = "set"; }
optionalAttrs (false) { my = "set"; }
=> { }
Located at lib/attrsets.nix:1350 in <nixpkgs>
.
lib.attrsets.zipAttrsWithNames
Merge sets of attributes and use the function f
to merge attributes
values.
names
List of attribute names to zip.
f
A function, accepts an attribute name, all the values, and returns a combined value.
sets
List of values from the list of attribute sets.
zipAttrsWithNames :: [ String ] -> (String -> [ Any ] -> Any) -> [ AttrSet ] -> AttrSet
lib.attrsets.zipAttrsWithNames
usage examplezipAttrsWithNames ["a"] (name: vs: vs) [{a = "x";} {a = "y"; b = "z";}]
=> { a = ["x" "y"]; }
Located at lib/attrsets.nix:1392 in <nixpkgs>
.
lib.attrsets.zipAttrsWith
Merge sets of attributes and use the function f to merge attribute values.
Like lib.attrsets.zipAttrsWithNames
with all key names are passed for names
.
Implementation note: Common names appear multiple times in the list of
names, hopefully this does not affect the system because the maximal
laziness avoid computing twice the same expression and listToAttrs
does
not care about duplicated attribute names.
zipAttrsWith :: (String -> [ Any ] -> Any) -> [ AttrSet ] -> AttrSet
lib.attrsets.zipAttrsWith
usage examplezipAttrsWith (name: values: values) [{a = "x";} {a = "y"; b = "z";}]
=> { a = ["x" "y"]; b = ["z"]; }
Located at lib/attrsets.nix:1428 in <nixpkgs>
.
lib.attrsets.zipAttrs
Merge sets of attributes and combine each attribute value in to a list.
Like lib.attrsets.zipAttrsWith
with (name: values: values)
as the function.
zipAttrs :: [ AttrSet ] -> AttrSet
lib.attrsets.zipAttrs
usage examplezipAttrs [{a = "x";} {a = "y"; b = "z";}]
=> { a = ["x" "y"]; b = ["z"]; }
Located at lib/attrsets.nix:1454 in <nixpkgs>
.
lib.attrsets.mergeAttrsList
Merge a list of attribute sets together using the //
operator.
In case of duplicate attributes, values from later list elements take precedence over earlier ones.
The result is the same as foldl mergeAttrs { }
, but the performance is better for large inputs.
For n list elements, each with an attribute set containing m unique attributes, the complexity of this operation is O(nm log n).
list
1. Function argument
mergeAttrsList :: [ Attrs ] -> Attrs
lib.attrsets.mergeAttrsList
usage examplemergeAttrsList [ { a = 0; b = 1; } { c = 2; d = 3; } ]
=> { a = 0; b = 1; c = 2; d = 3; }
mergeAttrsList [ { a = 0; } { a = 1; } ]
=> { a = 1; }
Located at lib/attrsets.nix:1488 in <nixpkgs>
.
lib.attrsets.recursiveUpdateUntil
Does the same as the update operator ‘//’ except that attributes are merged until the given predicate is verified. The predicate should accept 3 arguments which are the path to reach the attribute, a part of the first attribute set and a part of the second attribute set. When the predicate is satisfied, the value of the first attribute set is replaced by the value of the second attribute set.
pred
Predicate, taking the path to the current attribute as a list of strings for attribute names, and the two values at that path from the original arguments.
lhs
Left attribute set of the merge.
rhs
Right attribute set of the merge.
recursiveUpdateUntil :: ( [ String ] -> AttrSet -> AttrSet -> Bool ) -> AttrSet -> AttrSet -> AttrSet
lib.attrsets.recursiveUpdateUntil
usage examplerecursiveUpdateUntil (path: l: r: path == ["foo"]) {
# first attribute set
foo.bar = 1;
foo.baz = 2;
bar = 3;
} {
#second attribute set
foo.bar = 1;
foo.quz = 2;
baz = 4;
}
=> {
foo.bar = 1; # 'foo.*' from the second set
foo.quz = 2; #
bar = 3; # 'bar' from the first set
baz = 4; # 'baz' from the second set
}
Located at lib/attrsets.nix:1566 in <nixpkgs>
.
lib.attrsets.recursiveUpdate
A recursive variant of the update operator ‘//’. The recursion stops when one of the attribute values is not an attribute set, in which case the right hand side value takes precedence over the left hand side value.
lhs
Left attribute set of the merge.
rhs
Right attribute set of the merge.
recursiveUpdate :: AttrSet -> AttrSet -> AttrSet
lib.attrsets.recursiveUpdate
usage examplerecursiveUpdate {
boot.loader.grub.enable = true;
boot.loader.grub.device = "/dev/hda";
} {
boot.loader.grub.device = "";
}
returns: {
boot.loader.grub.enable = true;
boot.loader.grub.device = "";
}
Located at lib/attrsets.nix:1625 in <nixpkgs>
.
lib.attrsets.matchAttrs
Recurse into every attribute set of the first argument and check that:
Each attribute path also exists in the second argument.
If the attribute’s value is not a nested attribute set, it must have the same value in the right argument.
pattern
Attribute set structure to match
attrs
Attribute set to check
matchAttrs :: AttrSet -> AttrSet -> Bool
lib.attrsets.matchAttrs
usage examplematchAttrs { cpu = {}; } { cpu = { bits = 64; }; }
=> true
Located at lib/attrsets.nix:1664 in <nixpkgs>
.
lib.attrsets.overrideExisting
Override only the attributes that are already present in the old set useful for deep-overriding.
old
Original attribute set
new
Attribute set with attributes to override in old
.
overrideExisting :: AttrSet -> AttrSet -> AttrSet
lib.attrsets.overrideExisting
usage exampleoverrideExisting {} { a = 1; }
=> {}
overrideExisting { b = 2; } { a = 1; }
=> { b = 2; }
overrideExisting { a = 3; b = 2; } { a = 1; }
=> { a = 1; b = 2; }
Located at lib/attrsets.nix:1720 in <nixpkgs>
.
lib.attrsets.showAttrPath
Turns a list of strings into a human-readable description of those
strings represented as an attribute path. The result of this function is
not intended to be machine-readable.
Create a new attribute set with value
set at the nested attribute location specified in attrPath
.
path
Attribute path to render to a string
showAttrPath :: [String] -> String
lib.attrsets.showAttrPath
usage exampleshowAttrPath [ "foo" "10" "bar" ]
=> "foo.\"10\".bar"
showAttrPath []
=> "<root attribute path>"
Located at lib/attrsets.nix:1758 in <nixpkgs>
.
lib.attrsets.getOutput
Get a package output.
If no output is found, fallback to .out
and then to the default.
The function is idempotent: getOutput "b" (getOutput "a" p) == getOutput "a" p
.
output
1. Function argument
pkg
2. Function argument
getOutput :: String -> :: Derivation -> Derivation
lib.attrsets.getOutput
usage example"${getOutput "dev" pkgs.openssl}"
=> "/nix/store/9rz8gxhzf8sw4kf2j2f1grr49w8zx5vj-openssl-1.0.1r-dev"
Located at lib/attrsets.nix:1797 in <nixpkgs>
.
lib.attrsets.getFirstOutput
Get the first of the outputs
provided by the package, or the default.
This function is alligned with _overrideFirst()
from the multiple-outputs.sh
setup hook.
Like getOutput
, the function is idempotent.
outputs
1. Function argument
pkg
2. Function argument
getFirstOutput :: [String] -> Derivation -> Derivation
lib.attrsets.getFirstOutput
usage example"${getFirstOutput [ "include" "dev" ] pkgs.openssl}"
=> "/nix/store/00000000000000000000000000000000-openssl-1.0.1r-dev"
Located at lib/attrsets.nix:1834 in <nixpkgs>
.
lib.attrsets.getBin
Get a package’s bin
output.
If the output does not exist, fallback to .out
and then to the default.
pkg
The package whose bin
output will be retrieved.
getBin :: Derivation -> Derivation
lib.attrsets.getBin
usage example"${getBin pkgs.openssl}"
=> "/nix/store/00000000000000000000000000000000-openssl-1.0.1r"
Located at lib/attrsets.nix:1872 in <nixpkgs>
.
lib.attrsets.getLib
Get a package’s lib
output.
If the output does not exist, fallback to .out
and then to the default.
pkg
The package whose lib
output will be retrieved.
getLib :: Derivation -> Derivation
lib.attrsets.getLib
usage example"${getLib pkgs.openssl}"
=> "/nix/store/9rz8gxhzf8sw4kf2j2f1grr49w8zx5vj-openssl-1.0.1r-lib"
Located at lib/attrsets.nix:1902 in <nixpkgs>
.
lib.attrsets.getStatic
Get a package’s static
output.
If the output does not exist, fallback to .lib
, then to .out
, and then to the default.
pkg
The package whose static
output will be retrieved.
getStatic :: Derivation -> Derivation
lib.attrsets.getStatic
usage example"${lib.getStatic pkgs.glibc}"
=> "/nix/store/00000000000000000000000000000000-glibc-2.39-52-static"
Located at lib/attrsets.nix:1931 in <nixpkgs>
.
lib.attrsets.getDev
Get a package’s dev
output.
If the output does not exist, fallback to .out
and then to the default.
pkg
The package whose dev
output will be retrieved.
getDev :: Derivation -> Derivation
lib.attrsets.getDev
usage example"${getDev pkgs.openssl}"
=> "/nix/store/9rz8gxhzf8sw4kf2j2f1grr49w8zx5vj-openssl-1.0.1r-dev"
Located at lib/attrsets.nix:1961 in <nixpkgs>
.
lib.attrsets.getInclude
Get a package’s include
output.
If the output does not exist, fallback to .dev
, then to .out
, and then to the default.
pkg
The package whose include
output will be retrieved.
getInclude :: Derivation -> Derivation
lib.attrsets.getInclude
usage example"${getInclude pkgs.openssl}"
=> "/nix/store/00000000000000000000000000000000-openssl-1.0.1r-dev"
Located at lib/attrsets.nix:1990 in <nixpkgs>
.
lib.attrsets.getMan
Get a package’s man
output.
If the output does not exist, fallback to .out
and then to the default.
pkg
The package whose man
output will be retrieved.
getMan :: Derivation -> Derivation
lib.attrsets.getMan
usage example"${getMan pkgs.openssl}"
=> "/nix/store/9rz8gxhzf8sw4kf2j2f1grr49w8zx5vj-openssl-1.0.1r-man"
Located at lib/attrsets.nix:2020 in <nixpkgs>
.
lib.attrsets.chooseDevOutputs
Pick the outputs of packages to place in buildInputs
pkgs
List of packages.
chooseDevOutputs :: [Derivation] -> [Derivation]
Located at lib/attrsets.nix:2037 in <nixpkgs>
.
lib.attrsets.recurseIntoAttrs
Make various Nix tools consider the contents of the resulting attribute set when looking for what to build, find, etc.
This function only affects a single attribute set; it does not apply itself recursively for nested attribute sets.
attrs
An attribute set to scan for derivations.
recurseIntoAttrs :: AttrSet -> AttrSet
lib.attrsets.recurseIntoAttrs
usage example{ pkgs ? import <nixpkgs> {} }:
{
myTools = pkgs.lib.recurseIntoAttrs {
inherit (pkgs) hello figlet;
};
}
Located at lib/attrsets.nix:2074 in <nixpkgs>
.
lib.attrsets.dontRecurseIntoAttrs
Undo the effect of recurseIntoAttrs.
attrs
An attribute set to not scan for derivations.
lib.attrsets.unionOfDisjoint
unionOfDisjoint x y
is equal to x // y // z
where the
attrnames in z
are the intersection of the attrnames in x
and
y
, and all values assert
with an error message. This
operator is commutative, unlike (//).
x
1. Function argument
y
2. Function argument
unionOfDisjoint :: AttrSet -> AttrSet -> AttrSet
Located at lib/attrsets.nix:2121 in <nixpkgs>
.
String manipulation functions.
lib.strings.concatStrings
Concatenate a list of strings.
concatStrings :: [string] -> string
lib.strings.concatStrings
usage exampleconcatStrings ["foo" "bar"]
=> "foobar"
Located at lib/strings.nix:64 in <nixpkgs>
.
lib.strings.concatMapStrings
Map a function over a list and concatenate the resulting strings.
f
1. Function argument
list
2. Function argument
concatMapStrings :: (a -> string) -> [a] -> string
lib.strings.concatMapStrings
usage exampleconcatMapStrings (x: "a" + x) ["foo" "bar"]
=> "afooabar"
Located at lib/strings.nix:95 in <nixpkgs>
.
lib.strings.concatImapStrings
Like concatMapStrings
except that the f functions also gets the
position as a parameter.
f
1. Function argument
list
2. Function argument
concatImapStrings :: (int -> a -> string) -> [a] -> string
lib.strings.concatImapStrings
usage exampleconcatImapStrings (pos: x: "${toString pos}-${x}") ["foo" "bar"]
=> "1-foo2-bar"
Located at lib/strings.nix:127 in <nixpkgs>
.
lib.strings.intersperse
Place an element between each element of a list
separator
Separator to add between elements
list
Input list
intersperse :: a -> [a] -> [a]
lib.strings.intersperse
usage exampleintersperse "/" ["usr" "local" "bin"]
=> ["usr" "/" "local" "/" "bin"].
Located at lib/strings.nix:158 in <nixpkgs>
.
lib.strings.concatStringsSep
Concatenate a list of strings with a separator between each element
sep
Separator to add between elements
list
List of input strings
concatStringsSep :: string -> [string] -> string
lib.strings.concatStringsSep
usage exampleconcatStringsSep "/" ["usr" "local" "bin"]
=> "usr/local/bin"
Located at lib/strings.nix:193 in <nixpkgs>
.
lib.strings.concatMapStringsSep
Maps a function over a list of strings and then concatenates the result with the specified separator interspersed between elements.
sep
Separator to add between elements
f
Function to map over the list
list
List of input strings
concatMapStringsSep :: string -> (a -> string) -> [a] -> string
lib.strings.concatMapStringsSep
usage exampleconcatMapStringsSep "-" (x: toUpper x) ["foo" "bar" "baz"]
=> "FOO-BAR-BAZ"
Located at lib/strings.nix:229 in <nixpkgs>
.
lib.strings.concatImapStringsSep
Same as concatMapStringsSep
, but the mapping function
additionally receives the position of its argument.
sep
Separator to add between elements
f
Function that receives elements and their positions
list
List of input strings
concatIMapStringsSep :: string -> (int -> a -> string) -> [a] -> string
lib.strings.concatImapStringsSep
usage exampleconcatImapStringsSep "-" (pos: x: toString (x / pos)) [ 6 6 6 ]
=> "6-3-2"
Located at lib/strings.nix:267 in <nixpkgs>
.
lib.strings.concatLines
Concatenate a list of strings, adding a newline at the end of each one.
Defined as concatMapStrings (s: s + "\n")
.
list
List of strings. Any element that is not a string will be implicitly converted to a string.
concatLines :: [string] -> string
lib.strings.concatLines
usage exampleconcatLines [ "foo" "bar" ]
=> "foo\nbar\n"
Located at lib/strings.nix:298 in <nixpkgs>
.
lib.strings.replicate
Repeat a string n
times,
and concatenate the parts into a new string.
n
1. Function argument
s
2. Function argument
replicate :: int -> string -> string
lib.strings.replicate
usage examplereplicate 3 "v"
=> "vvv"
replicate 5 "hello"
=> "hellohellohellohellohello"
Located at lib/strings.nix:332 in <nixpkgs>
.
lib.strings.trim
Remove leading and trailing whitespace from a string s
.
Whitespace is defined as any of the following characters: " ", “\t” “\r” “\n”
s
The string to trim
trim :: string -> string
lib.strings.trim
usage exampletrim " hello, world! "
=> "hello, world!"
Located at lib/strings.nix:362 in <nixpkgs>
.
lib.strings.trimWith
Remove leading and/or trailing whitespace from a string s
.
To remove both leading and trailing whitespace, you can also use trim
Whitespace is defined as any of the following characters: " ", “\t” “\r” “\n”
config
(Attribute set)start
Whether to trim leading whitespace (false
by default)
end
Whether to trim trailing whitespace (false
by default)
s
The string to trim
trimWith :: { start :: Bool; end :: Bool } -> String -> String
lib.strings.trimWith
usage exampletrimWith { start = true; } " hello, world! "}
=> "hello, world! "
trimWith { end = true; } " hello, world! "}
=> " hello, world!"
Located at lib/strings.nix:406 in <nixpkgs>
.
lib.strings.makeSearchPath
Construct a Unix-style, colon-separated search path consisting of
the given subDir
appended to each of the given paths.
subDir
Directory name to append
paths
List of base paths
makeSearchPath :: string -> [string] -> string
lib.strings.makeSearchPath
usage examplemakeSearchPath "bin" ["/root" "/usr" "/usr/local"]
=> "/root/bin:/usr/bin:/usr/local/bin"
makeSearchPath "bin" [""]
=> "/bin"
Located at lib/strings.nix:467 in <nixpkgs>
.
lib.strings.makeSearchPathOutput
Construct a Unix-style search path by appending the given
subDir
to the specified output
of each of the packages.
If no output by the given name is found, fallback to .out
and then to
the default.
output
Package output to use
subDir
Directory name to append
pkgs
List of packages
makeSearchPathOutput :: string -> string -> [package] -> string
lib.strings.makeSearchPathOutput
usage examplemakeSearchPathOutput "dev" "bin" [ pkgs.openssl pkgs.zlib ]
=> "/nix/store/9rz8gxhzf8sw4kf2j2f1grr49w8zx5vj-openssl-1.0.1r-dev/bin:/nix/store/wwh7mhwh269sfjkm6k5665b5kgp7jrk2-zlib-1.2.8/bin"
Located at lib/strings.nix:508 in <nixpkgs>
.
lib.strings.makeLibraryPath
Construct a library search path (such as RPATH) containing the libraries for a set of packages
packages
List of packages
makeLibraryPath :: [package] -> string
lib.strings.makeLibraryPath
usage examplemakeLibraryPath [ "/usr" "/usr/local" ]
=> "/usr/lib:/usr/local/lib"
pkgs = import <nixpkgs> { }
makeLibraryPath [ pkgs.openssl pkgs.zlib ]
=> "/nix/store/9rz8gxhzf8sw4kf2j2f1grr49w8zx5vj-openssl-1.0.1r/lib:/nix/store/wwh7mhwh269sfjkm6k5665b5kgp7jrk2-zlib-1.2.8/lib"
Located at lib/strings.nix:542 in <nixpkgs>
.
lib.strings.makeIncludePath
Construct an include search path (such as C_INCLUDE_PATH) containing the header files for a set of packages or paths.
packages
List of packages
makeIncludePath :: [package] -> string
lib.strings.makeIncludePath
usage examplemakeIncludePath [ "/usr" "/usr/local" ]
=> "/usr/include:/usr/local/include"
pkgs = import <nixpkgs> { }
makeIncludePath [ pkgs.openssl pkgs.zlib ]
=> "/nix/store/9rz8gxhzf8sw4kf2j2f1grr49w8zx5vj-openssl-1.0.1r-dev/include:/nix/store/wwh7mhwh269sfjkm6k5665b5kgp7jrk2-zlib-1.2.8-dev/include"
Located at lib/strings.nix:573 in <nixpkgs>
.
lib.strings.makeBinPath
Construct a binary search path (such as $PATH) containing the binaries for a set of packages.
packages
List of packages
makeBinPath :: [package] -> string
lib.strings.makeBinPath
usage examplemakeBinPath ["/root" "/usr" "/usr/local"]
=> "/root/bin:/usr/bin:/usr/local/bin"
Located at lib/strings.nix:601 in <nixpkgs>
.
lib.strings.normalizePath
Normalize path, removing extraneous /s
s
1. Function argument
normalizePath :: string -> string
lib.strings.normalizePath
usage examplenormalizePath "/a//b///c/"
=> "/a/b/c/"
Located at lib/strings.nix:629 in <nixpkgs>
.
lib.strings.optionalString
Depending on the boolean `cond’, return either the given string or the empty string. Useful to concatenate against a bigger string.
cond
Condition
string
String to return if condition is true
optionalString :: bool -> string -> string
lib.strings.optionalString
usage exampleoptionalString true "some-string"
=> "some-string"
optionalString false "some-string"
=> ""
Located at lib/strings.nix:676 in <nixpkgs>
.
lib.strings.hasPrefix
Determine whether a string has given prefix.
pref
Prefix to check for
str
Input string
hasPrefix :: string -> string -> bool
lib.strings.hasPrefix
usage examplehasPrefix "foo" "foobar"
=> true
hasPrefix "foo" "barfoo"
=> false
Located at lib/strings.nix:711 in <nixpkgs>
.
lib.strings.hasSuffix
Determine whether a string has given suffix.
suffix
Suffix to check for
content
Input string
hasSuffix :: string -> string -> bool
lib.strings.hasSuffix
usage examplehasSuffix "foo" "foobar"
=> false
hasSuffix "foo" "barfoo"
=> true
Located at lib/strings.nix:757 in <nixpkgs>
.
lib.strings.hasInfix
Determine whether a string contains the given infix
infix
1. Function argument
content
2. Function argument
hasInfix :: string -> string -> bool
lib.strings.hasInfix
usage examplehasInfix "bc" "abcd"
=> true
hasInfix "ab" "abcd"
=> true
hasInfix "cd" "abcd"
=> true
hasInfix "foo" "abcd"
=> false
Located at lib/strings.nix:813 in <nixpkgs>
.
lib.strings.stringToCharacters
Convert a string s
to a list of characters (i.e. singleton strings).
This allows you to, e.g., map a function over each character. However,
note that this will likely be horribly inefficient; Nix is not a
general purpose programming language. Complex string manipulations
should, if appropriate, be done in a derivation.
Also note that Nix treats strings as a list of bytes and thus doesn’t
handle unicode.
s
1. Function argument
stringToCharacters :: string -> [string]
lib.strings.stringToCharacters
usage examplestringToCharacters ""
=> [ ]
stringToCharacters "abc"
=> [ "a" "b" "c" ]
stringToCharacters "🦄"
=> [ "�" "�" "�" "�" ]
Located at lib/strings.nix:861 in <nixpkgs>
.
lib.strings.stringAsChars
Manipulate a string character by character and replace them by strings before concatenating the results.
f
Function to map over each individual character
s
Input string
stringAsChars :: (string -> string) -> string -> string
lib.strings.stringAsChars
usage examplestringAsChars (x: if x == "a" then "i" else x) "nax"
=> "nix"
Located at lib/strings.nix:894 in <nixpkgs>
.
lib.strings.charToInt
Convert char to ascii value, must be in printable range
c
1. Function argument
charToInt :: string -> int
lib.strings.charToInt
usage examplecharToInt "A"
=> 65
charToInt "("
=> 40
Located at lib/strings.nix:930 in <nixpkgs>
.
lib.strings.escape
Escape occurrence of the elements of list
in string
by
prefixing it with a backslash.
list
1. Function argument
string
2. Function argument
escape :: [string] -> string -> string
lib.strings.escape
usage exampleescape ["(" ")"] "(foo)"
=> "\\(foo\\)"
Located at lib/strings.nix:962 in <nixpkgs>
.
lib.strings.escapeC
Escape occurrence of the element of list
in string
by
converting to its ASCII value and prefixing it with \x.
Only works for printable ascii characters.
list
1. Function argument
string
2. Function argument
escapeC = [string] -> string -> string
lib.strings.escapeC
usage exampleescapeC [" "] "foo bar"
=> "foo\\x20bar"
Located at lib/strings.nix:995 in <nixpkgs>
.
lib.strings.escapeURL
Escape the string
so it can be safely placed inside a URL
query.
string
1. Function argument
escapeURL :: string -> string
lib.strings.escapeURL
usage exampleescapeURL "foo/bar baz"
=> "foo%2Fbar%20baz"
Located at lib/strings.nix:1023 in <nixpkgs>
.
lib.strings.escapeShellArg
Quote string
to be used safely within the Bourne shell if it has any
special characters.
string
1. Function argument
escapeShellArg :: string -> string
lib.strings.escapeShellArg
usage exampleescapeShellArg "esc'ape\nme"
=> "'esc'\\''ape\nme'"
Located at lib/strings.nix:1056 in <nixpkgs>
.
lib.strings.escapeShellArgs
Quote all arguments that have special characters to be safely passed to the Bourne shell.
args
1. Function argument
escapeShellArgs :: [string] -> string
lib.strings.escapeShellArgs
usage exampleescapeShellArgs ["one" "two three" "four'five"]
=> "one 'two three' 'four'\\''five'"
Located at lib/strings.nix:1090 in <nixpkgs>
.
lib.strings.isValidPosixName
Test whether the given name
is a valid POSIX shell variable name.
name
1. Function argument
string -> bool
lib.strings.isValidPosixName
usage exampleisValidPosixName "foo_bar000"
=> true
isValidPosixName "0-bad.jpg"
=> false
Located at lib/strings.nix:1120 in <nixpkgs>
.
lib.strings.toShellVar
Translate a Nix value into a shell variable declaration, with proper escaping.
The value can be a string (mapped to a regular variable), a list of strings (mapped to a Bash-style array) or an attribute set of strings (mapped to a Bash-style associative array). Note that “string” includes string-coercible values like paths or derivations.
Strings are translated into POSIX sh-compatible code; lists and attribute sets assume a shell that understands Bash syntax (e.g. Bash or ZSH).
name
1. Function argument
value
2. Function argument
string -> ( string | [string] | { ${name} :: string; } ) -> string
lib.strings.toShellVar
usage example''
${toShellVar "foo" "some string"}
[[ "$foo" == "some string" ]]
''
Located at lib/strings.nix:1161 in <nixpkgs>
.
lib.strings.toShellVars
Translate an attribute set vars
into corresponding shell variable declarations
using toShellVar
.
vars
1. Function argument
toShellVars :: {
${name} :: string | [ string ] | { ${key} :: string; };
} -> string
lib.strings.toShellVars
usage examplelet
foo = "value";
bar = foo;
in ''
${toShellVars { inherit foo bar; }}
[[ "$foo" == "$bar" ]]
''
Located at lib/strings.nix:1209 in <nixpkgs>
.
lib.strings.escapeNixString
Turn a string s
into a Nix expression representing that string
s
1. Function argument
escapeNixString :: string -> string
lib.strings.escapeNixString
usage exampleescapeNixString "hello\${}\n"
=> "\"hello\\\${}\\n\""
Located at lib/strings.nix:1236 in <nixpkgs>
.
lib.strings.escapeRegex
Turn a string s
into an exact regular expression
s
1. Function argument
escapeRegex :: string -> string
lib.strings.escapeRegex
usage exampleescapeRegex "[^a-z]*"
=> "\\[\\^a-z]\\*"
Located at lib/strings.nix:1263 in <nixpkgs>
.
lib.strings.escapeNixIdentifier
Quotes a string s
if it can’t be used as an identifier directly.
s
1. Function argument
escapeNixIdentifier :: string -> string
lib.strings.escapeNixIdentifier
usage exampleescapeNixIdentifier "hello"
=> "hello"
escapeNixIdentifier "0abc"
=> "\"0abc\""
Located at lib/strings.nix:1293 in <nixpkgs>
.
lib.strings.escapeXML
Escapes a string s
such that it is safe to include verbatim in an XML
document.
s
1. Function argument
escapeXML :: string -> string
lib.strings.escapeXML
usage exampleescapeXML ''"test" 'test' < & >''
=> ""test" 'test' < & >"
Located at lib/strings.nix:1324 in <nixpkgs>
.
lib.strings.toLower
Converts an ASCII string s
to lower-case.
s
The string to convert to lower-case.
toLower :: string -> string
lib.strings.toLower
usage exampletoLower "HOME"
=> "home"
Located at lib/strings.nix:1360 in <nixpkgs>
.
lib.strings.toUpper
Converts an ASCII string s
to upper-case.
s
The string to convert to upper-case.
toUpper :: string -> string
lib.strings.toUpper
usage exampletoUpper "home"
=> "HOME"
Located at lib/strings.nix:1388 in <nixpkgs>
.
lib.strings.addContextFrom
Appends string context from string like object src
to target
.
This is an implementation detail of Nix and should be used carefully.
Strings in Nix carry an invisible context
which is a list of strings
representing store paths. If the string is later used in a derivation
attribute, the derivation will properly populate the inputDrvs and
inputSrcs.
src
The string to take the context from. If the argument is not a string, it will be implicitly converted to a string.
target
The string to append the context to. If the argument is not a string, it will be implicitly converted to a string.
addContextFrom :: string -> string -> string
lib.strings.addContextFrom
usage examplepkgs = import <nixpkgs> { };
addContextFrom pkgs.coreutils "bar"
=> "bar"
The context can be displayed using the toString
function:
nix-repl> builtins.getContext (lib.strings.addContextFrom pkgs.coreutils "bar")
{
"/nix/store/m1s1d2dk2dqqlw3j90jl3cjy2cykbdxz-coreutils-9.5.drv" = { ... };
}
Located at lib/strings.nix:1441 in <nixpkgs>
.
lib.strings.splitString
Cut a string with a separator and produces a list of strings which were separated by this separator.
sep
1. Function argument
s
2. Function argument
splitString :: string -> string -> [string]
lib.strings.splitString
usage examplesplitString "." "foo.bar.baz"
=> [ "foo" "bar" "baz" ]
splitString "/" "/usr/local/bin"
=> [ "" "usr" "local" "bin" ]
Located at lib/strings.nix:1474 in <nixpkgs>
.
lib.strings.removePrefix
Return a string without the specified prefix, if the prefix matches.
prefix
Prefix to remove if it matches
str
Input string
removePrefix :: string -> string -> string
lib.strings.removePrefix
usage exampleremovePrefix "foo." "foo.bar.baz"
=> "bar.baz"
removePrefix "xxx" "foo.bar.baz"
=> "foo.bar.baz"
Located at lib/strings.nix:1511 in <nixpkgs>
.
lib.strings.removeSuffix
Return a string without the specified suffix, if the suffix matches.
suffix
Suffix to remove if it matches
str
Input string
removeSuffix :: string -> string -> string
lib.strings.removeSuffix
usage exampleremoveSuffix "front" "homefront"
=> "home"
removeSuffix "xxx" "homefront"
=> "homefront"
Located at lib/strings.nix:1563 in <nixpkgs>
.
lib.strings.versionOlder
Return true if string v1
denotes a version older than v2
.
v1
1. Function argument
v2
2. Function argument
versionOlder :: String -> String -> Bool
lib.strings.versionOlder
usage exampleversionOlder "1.1" "1.2"
=> true
versionOlder "1.1" "1.1"
=> false
Located at lib/strings.nix:1615 in <nixpkgs>
.
lib.strings.versionAtLeast
Return true if string v1 denotes a version equal to or newer than v2.
v1
1. Function argument
v2
2. Function argument
versionAtLeast :: String -> String -> Bool
lib.strings.versionAtLeast
usage exampleversionAtLeast "1.1" "1.0"
=> true
versionAtLeast "1.1" "1.1"
=> true
versionAtLeast "1.1" "1.2"
=> false
Located at lib/strings.nix:1650 in <nixpkgs>
.
lib.strings.getName
This function takes an argument x
that’s either a derivation or a
derivation’s “name” attribute and extracts the name part from that
argument.
x
1. Function argument
getName :: String | Derivation -> String
lib.strings.getName
usage examplegetName "youtube-dl-2016.01.01"
=> "youtube-dl"
getName pkgs.youtube-dl
=> "youtube-dl"
Located at lib/strings.nix:1682 in <nixpkgs>
.
lib.strings.getVersion
This function takes an argument x
that’s either a derivation or a
derivation’s “name” attribute and extracts the version part from that
argument.
x
1. Function argument
getVersion :: String | Derivation -> String
lib.strings.getVersion
usage examplegetVersion "youtube-dl-2016.01.01"
=> "2016.01.01"
getVersion pkgs.youtube-dl
=> "2016.01.01"
Located at lib/strings.nix:1719 in <nixpkgs>
.
lib.strings.nameFromURL
Extract name and version from a URL as shown in the examples.
Separator sep
is used to determine the end of the extension.
url
1. Function argument
sep
2. Function argument
nameFromURL :: String -> String
lib.strings.nameFromURL
usage examplenameFromURL "https://nixos.org/releases/nix/nix-1.7/nix-1.7-x86_64-linux.tar.bz2" "-"
=> "nix"
nameFromURL "https://nixos.org/releases/nix/nix-1.7/nix-1.7-x86_64-linux.tar.bz2" "_"
=> "nix-1.7-x86"
Located at lib/strings.nix:1759 in <nixpkgs>
.
lib.strings.cmakeOptionType
Create a "-D<feature>:<type>=<value>"
string that can be passed to typical
CMake invocations.
feature
The feature to be set
type
The type of the feature to be set, as described in https://cmake.org/cmake/help/latest/command/set.html the possible values (case insensitive) are: BOOL FILEPATH PATH STRING INTERNAL
value
The desired value
cmakeOptionType :: string -> string -> string -> string
lib.strings.cmakeOptionType
usage examplecmakeOptionType "string" "ENGINE" "sdl2"
=> "-DENGINE:STRING=sdl2"
Located at lib/strings.nix:1801 in <nixpkgs>
.
lib.strings.cmakeBool
Create a -D<condition>={TRUE,FALSE} string that can be passed to typical CMake invocations.
condition
The condition to be made true or false
flag
The controlling flag of the condition
cmakeBool :: string -> bool -> string
lib.strings.cmakeBool
usage examplecmakeBool "ENABLE_STATIC_LIBS" false
=> "-DENABLESTATIC_LIBS:BOOL=FALSE"
Located at lib/strings.nix:1839 in <nixpkgs>
.
lib.strings.cmakeFeature
Create a -D<feature>:STRING=<value> string that can be passed to typical CMake invocations. This is the most typical usage, so it deserves a special case.
feature
The feature to be set
value
The desired value
cmakeFeature :: string -> string -> string
lib.strings.cmakeFeature
usage examplecmakeFeature "MODULES" "badblock"
=> "-DMODULES:STRING=badblock"
Located at lib/strings.nix:1876 in <nixpkgs>
.
lib.strings.mesonOption
Create a -D<feature>=<value> string that can be passed to typical Meson invocations.
feature
The feature to be set
value
The desired value
mesonOption :: string -> string -> string
lib.strings.mesonOption
usage examplemesonOption "engine" "opengl"
=> "-Dengine=opengl"
Located at lib/strings.nix:1911 in <nixpkgs>
.
lib.strings.mesonBool
Create a -D<condition>={true,false} string that can be passed to typical Meson invocations.
condition
The condition to be made true or false
flag
The controlling flag of the condition
mesonBool :: string -> bool -> string
lib.strings.mesonBool
usage examplemesonBool "hardened" true
=> "-Dhardened=true"
mesonBool "static" false
=> "-Dstatic=false"
Located at lib/strings.nix:1948 in <nixpkgs>
.
lib.strings.mesonEnable
Create a -D<feature>={enabled,disabled} string that can be passed to typical Meson invocations.
feature
The feature to be enabled or disabled
flag
The controlling flag
mesonEnable :: string -> bool -> string
lib.strings.mesonEnable
usage examplemesonEnable "docs" true
=> "-Ddocs=enabled"
mesonEnable "savage" false
=> "-Dsavage=disabled"
Located at lib/strings.nix:1985 in <nixpkgs>
.
lib.strings.enableFeature
Create an --{enable,disable}-<feature> string that can be passed to standard GNU Autoconf scripts.
flag
1. Function argument
feature
2. Function argument
enableFeature :: bool -> string -> string
lib.strings.enableFeature
usage exampleenableFeature true "shared"
=> "--enable-shared"
enableFeature false "shared"
=> "--disable-shared"
Located at lib/strings.nix:2022 in <nixpkgs>
.
lib.strings.enableFeatureAs
Create an --{enable-<feature>=<value>,disable-<feature>} string that can be passed to standard GNU Autoconf scripts.
flag
1. Function argument
feature
2. Function argument
value
3. Function argument
enableFeatureAs :: bool -> string -> string -> string
lib.strings.enableFeatureAs
usage exampleenableFeatureAs true "shared" "foo"
=> "--enable-shared=foo"
enableFeatureAs false "shared" (throw "ignored")
=> "--disable-shared"
Located at lib/strings.nix:2062 in <nixpkgs>
.
lib.strings.withFeature
Create an --{with,without}-<feature> string that can be passed to standard GNU Autoconf scripts.
flag
1. Function argument
feature
2. Function argument
withFeature :: bool -> string -> string
lib.strings.withFeature
usage examplewithFeature true "shared"
=> "--with-shared"
withFeature false "shared"
=> "--without-shared"
Located at lib/strings.nix:2098 in <nixpkgs>
.
lib.strings.withFeatureAs
Create an --{with-<feature>=<value>,without-<feature>} string that can be passed to standard GNU Autoconf scripts.
flag
1. Function argument
feature
2. Function argument
value
3. Function argument
withFeatureAs :: bool -> string -> string -> string
lib.strings.withFeatureAs
usage examplewithFeatureAs true "shared" "foo"
=> "--with-shared=foo"
withFeatureAs false "shared" (throw "ignored")
=> "--without-shared"
Located at lib/strings.nix:2138 in <nixpkgs>
.
lib.strings.fixedWidthString
Create a fixed width string with additional prefix to match required width.
This function will fail if the input string is longer than the requested length.
width
1. Function argument
filler
2. Function argument
str
3. Function argument
fixedWidthString :: int -> string -> string -> string
lib.strings.fixedWidthString
usage examplefixedWidthString 5 "0" (toString 15)
=> "00015"
Located at lib/strings.nix:2177 in <nixpkgs>
.
lib.strings.fixedWidthNumber
Format a number adding leading zeroes up to fixed width.
width
1. Function argument
n
2. Function argument
fixedWidthNumber :: int -> int -> string
lib.strings.fixedWidthNumber
usage examplefixedWidthNumber 5 15
=> "00015"
Located at lib/strings.nix:2217 in <nixpkgs>
.
lib.strings.floatToString
Convert a float to a string, but emit a warning when precision is lost during the conversion
float
1. Function argument
floatToString :: float -> string
lib.strings.floatToString
usage examplefloatToString 0.000001
=> "0.000001"
floatToString 0.0000001
=> trace: warning: Imprecise conversion from float to string 0.000000
"0.000000"
Located at lib/strings.nix:2250 in <nixpkgs>
.
lib.strings.isCoercibleToString
Check whether a value val
can be coerced to a string.
Soft-deprecated function. While the original implementation is available as
isConvertibleWithToString
, consider using isStringLike
instead, if suitable.
val
1. Function argument
lib.strings.isConvertibleWithToString
Check whether a list or other value x
can be passed to toString.
Many types of value are coercible to string this way, including int
, float
,
null
, bool
, list
of similarly coercible values.
val
1. Function argument
lib.strings.isStringLike
Check whether a value can be coerced to a string. The value must be a string, path, or attribute set.
String-like values can be used without explicit conversion in string interpolations and in most functions that expect a string.
x
1. Function argument
lib.strings.isStorePath
Check whether a value x
is a store path.
x
1. Function argument
isStorePath :: a -> bool
lib.strings.isStorePath
usage exampleisStorePath "/nix/store/d945ibfx9x185xf04b890y4f9g3cbb63-python-2.7.11/bin/python"
=> false
isStorePath "/nix/store/d945ibfx9x185xf04b890y4f9g3cbb63-python-2.7.11"
=> true
isStorePath pkgs.python
=> true
isStorePath [] || isStorePath 42 || isStorePath {} || …
=> false
Located at lib/strings.nix:2360 in <nixpkgs>
.
lib.strings.toInt
Parse a string as an int. Does not support parsing of integers with preceding zero due to ambiguity between zero-padded and octal numbers. See toIntBase10.
str
A string to be interpreted as an int.
toInt :: string -> int
lib.strings.toInt
usage exampletoInt "1337"
=> 1337
toInt "-4"
=> -4
toInt " 123 "
=> 123
toInt "00024"
=> error: Ambiguity in interpretation of 00024 between octal and zero padded integer.
toInt "3.14"
=> error: floating point JSON numbers are not supported
Located at lib/strings.nix:2406 in <nixpkgs>
.
lib.strings.toIntBase10
Parse a string as a base 10 int. This supports parsing of zero-padded integers.
str
A string to be interpreted as an int.
toIntBase10 :: string -> int
lib.strings.toIntBase10
usage exampletoIntBase10 "1337"
=> 1337
toIntBase10 "-4"
=> -4
toIntBase10 " 123 "
=> 123
toIntBase10 "00024"
=> 24
toIntBase10 "3.14"
=> error: floating point JSON numbers are not supported
Located at lib/strings.nix:2476 in <nixpkgs>
.
lib.strings.readPathsFromFile
Read a list of paths from file
, relative to the rootPath
.
Lines beginning with #
are treated as comments and ignored.
Whitespace is significant.
This function is deprecated and should be avoided.
This function is not performant and should be avoided.
rootPath
1. Function argument
file
2. Function argument
readPathsFromFile :: string -> string -> [string]
lib.strings.readPathsFromFile
usage examplereadPathsFromFile /prefix
./pkgs/development/libraries/qt-5/5.4/qtbase/series
=> [ "/prefix/dlopen-resolv.patch" "/prefix/tzdir.patch"
"/prefix/dlopen-libXcursor.patch" "/prefix/dlopen-openssl.patch"
"/prefix/dlopen-dbus.patch" "/prefix/xdg-config-dirs.patch"
"/prefix/nix-profiles-library-paths.patch"
"/prefix/compose-search-path.patch" ]
Located at lib/strings.nix:2552 in <nixpkgs>
.
lib.strings.fileContents
Read the contents of a file removing the trailing \n
file
1. Function argument
fileContents :: path -> string
lib.strings.fileContents
usage example$ echo "1.0" > ./version
fileContents ./version
=> "1.0"
Located at lib/strings.nix:2590 in <nixpkgs>
.
lib.strings.sanitizeDerivationName
Creates a valid derivation name from a potentially invalid one.
string
1. Function argument
sanitizeDerivationName :: String -> String
lib.strings.sanitizeDerivationName
usage examplesanitizeDerivationName "../hello.bar # foo"
=> "-hello.bar-foo"
sanitizeDerivationName ""
=> "unknown"
sanitizeDerivationName pkgs.hello
=> "-nix-store-2g75chlbpxlrqn15zlby2dfh8hr9qwbk-hello-2.10"
Located at lib/strings.nix:2622 in <nixpkgs>
.
lib.strings.levenshtein
Computes the Levenshtein distance between two strings a
and b
.
Complexity O(n*m) where n and m are the lengths of the strings. Algorithm adjusted from https://stackoverflow.com/a/9750974/6605742
a
1. Function argument
b
2. Function argument
levenshtein :: string -> string -> int
lib.strings.levenshtein
usage examplelevenshtein "foo" "foo"
=> 0
levenshtein "book" "hook"
=> 1
levenshtein "hello" "Heyo"
=> 3
Located at lib/strings.nix:2683 in <nixpkgs>
.
lib.strings.commonPrefixLength
Returns the length of the prefix that appears in both strings a
and b
.
a
1. Function argument
b
2. Function argument
lib.strings.commonSuffixLength
Returns the length of the suffix common to both strings a
and b
.
a
1. Function argument
b
2. Function argument
lib.strings.levenshteinAtMost
Returns whether the levenshtein distance between two strings a
and b
is at most some value k
.
Complexity is O(min(n,m)) for k <= 2 and O(n*m) otherwise
k
Distance threshold
a
String a
b
String b
levenshteinAtMost :: int -> string -> string -> bool
lib.strings.levenshteinAtMost
usage examplelevenshteinAtMost 0 "foo" "foo"
=> true
levenshteinAtMost 1 "foo" "boa"
=> false
levenshteinAtMost 2 "foo" "boa"
=> true
levenshteinAtMost 2 "This is a sentence" "this is a sentense."
=> false
levenshteinAtMost 3 "This is a sentence" "this is a sentense."
=> true
Located at lib/strings.nix:2791 in <nixpkgs>
.
Version string functions.
lib.versions.splitVersion
Break a version string into its component parts.
lib.versions.splitVersion
usage examplesplitVersion "1.2.3"
=> ["1" "2" "3"]
Located at lib/versions.nix:12 in <nixpkgs>
.
lib.versions.major
Get the major version string from a string.
v
Function argument
lib.versions.major
usage examplemajor "1.2.3"
=> "1"
Located at lib/versions.nix:20 in <nixpkgs>
.
lib.versions.minor
Get the minor version string from a string.
v
Function argument
lib.versions.minor
usage exampleminor "1.2.3"
=> "2"
Located at lib/versions.nix:28 in <nixpkgs>
.
lib.versions.patch
Get the patch version string from a string.
v
Function argument
lib.versions.patch
usage examplepatch "1.2.3"
=> "3"
Located at lib/versions.nix:36 in <nixpkgs>
.
lib.versions.majorMinor
Get string of the first two parts (major and minor) of a version string.
v
Function argument
lib.versions.majorMinor
usage examplemajorMinor "1.2.3"
=> "1.2"
Located at lib/versions.nix:45 in <nixpkgs>
.
lib.versions.pad
Pad a version string with zeros to match the given number of components.
n
Function argument
version
Function argument
lib.versions.pad
usage examplepad 3 "1.2"
=> "1.2.0"
pad 3 "1.3-rc1"
=> "1.3.0-rc1"
pad 3 "1.2.3.4"
=> "1.2.3"
Located at lib/versions.nix:59 in <nixpkgs>
.
lib.trivial.id
The identity function For when you need a function that does “nothing”.
x
The value to return
lib.trivial.const
The constant function
Ignores the second argument. If called with only one argument, constructs a function that always returns a static value.
x
Value to return
y
Value to ignore
const :: a -> b -> a
lib.trivial.const
usage examplelet f = const 5; in f 10
=> 5
Located at lib/trivial.nix:75 in <nixpkgs>
.
lib.trivial.pipe
Pipes a value through a list of functions, left to right.
value
Value to start piping.
fns
List of functions to apply sequentially.
pipe :: a -> [<functions>] -> <return type of last function>
lib.trivial.pipe
usage examplepipe 2 [
(x: x + 2) # 2 + 2 = 4
(x: x * 2) # 4 * 2 = 8
]
=> 8
# ideal to do text transformations
pipe [ "a/b" "a/c" ] [
# create the cp command
(map (file: ''cp "${src}/${file}" $out\n''))
# concatenate all commands into one string
lib.concatStrings
# make that string into a nix derivation
(pkgs.runCommand "copy-to-out" {})
]
=> <drv which copies all files to $out>
The output type of each function has to be the input type
of the next function, and the last function returns the
final value.
Located at lib/trivial.nix:131 in <nixpkgs>
.
lib.trivial.concat
Concatenate two lists
x
1. Function argument
y
2. Function argument
concat :: [a] -> [a] -> [a]
lib.trivial.concat
usage exampleconcat [ 1 2 ] [ 3 4 ]
=> [ 1 2 3 4 ]
Located at lib/trivial.nix:171 in <nixpkgs>
.
lib.trivial.or
boolean “or”
lib.trivial.and
boolean “and”
lib.trivial.xor
boolean “exclusive or”
lib.trivial.boolToString
Convert a boolean to a string.
This function uses the strings “true” and “false” to represent
boolean values. Calling toString
on a bool instead returns “1”
and “” (sic!).
b
1. Function argument
lib.trivial.mergeAttrs
Merge two attribute sets shallowly, right side trumps left
mergeAttrs :: attrs -> attrs -> attrs
x
Left attribute set
y
Right attribute set (higher precedence for equal keys)
lib.trivial.mergeAttrs
usage examplemergeAttrs { a = 1; b = 2; } { b = 3; c = 4; }
=> { a = 1; b = 3; c = 4; }
Located at lib/trivial.nix:278 in <nixpkgs>
.
lib.trivial.flip
Flip the order of the arguments of a binary function.
f
1. Function argument
a
2. Function argument
b
3. Function argument
flip :: (a -> b -> c) -> (b -> a -> c)
lib.trivial.flip
usage exampleflip concat [1] [2]
=> [ 2 1 ]
Located at lib/trivial.nix:317 in <nixpkgs>
.
lib.trivial.mapNullable
Apply function if the supplied argument is non-null.
f
Function to call
a
Argument to check for null before passing it to f
lib.trivial.mapNullable
usage examplemapNullable (x: x+1) null
=> null
mapNullable (x: x+1) 22
=> 23
Located at lib/trivial.nix:347 in <nixpkgs>
.
lib.trivial.version
Returns the current full nixpkgs version number.
Located at lib/trivial.nix:363 in <nixpkgs>
.
lib.trivial.release
Returns the current nixpkgs release number as string.
Located at lib/trivial.nix:368 in <nixpkgs>
.
lib.trivial.oldestSupportedRelease
The latest release that is supported, at the time of release branch-off, if applicable.
Ideally, out-of-tree modules should be able to evaluate cleanly with all supported Nixpkgs versions (master, release and old release until EOL). So if possible, deprecation warnings should take effect only when all out-of-tree expressions/libs/modules can upgrade to the new way without losing support for supported Nixpkgs versions.
This release number allows deprecation warnings to be implemented such that they take effect as soon as the oldest release reaches end of life.
Located at lib/trivial.nix:383 in <nixpkgs>
.
lib.trivial.isInOldestRelease
Whether a feature is supported in all supported releases (at the time of
release branch-off, if applicable). See oldestSupportedRelease
.
release
Release number of feature introduction as an integer, e.g. 2111 for 21.11. Set it to the upcoming release, matching the nixpkgs/.version file.
Located at lib/trivial.nix:399 in <nixpkgs>
.
lib.trivial.oldestSupportedReleaseIsAtLeast
Alias for isInOldestRelease
introduced in 24.11.
Use isInOldestRelease
in expressions outside of Nixpkgs for greater compatibility.
Located at lib/trivial.nix:408 in <nixpkgs>
.
lib.trivial.codeName
Returns the current nixpkgs release code name.
On each release the first letter is bumped and a new animal is chosen starting with that new letter.
Located at lib/trivial.nix:418 in <nixpkgs>
.
lib.trivial.versionSuffix
Returns the current nixpkgs version suffix as string.
Located at lib/trivial.nix:423 in <nixpkgs>
.
lib.trivial.revisionWithDefault
Attempts to return the the current revision of nixpkgs and returns the supplied default value otherwise.
default
Default value to return if revision can not be determined
lib.trivial.inNixShell
Determine whether the function is being called from inside a Nix shell.
lib.trivial.inPureEvalMode
Determine whether the function is being called from inside pure-eval mode
by seeing whether builtins
contains currentSystem
. If not, we must be in
pure-eval mode.
lib.trivial.min
Return minimum of two numbers.
lib.trivial.max
Return maximum of two numbers.
lib.trivial.mod
Integer modulus
base
1. Function argument
int
2. Function argument
lib.trivial.mod
usage examplemod 11 10
=> 1
mod 1 10
=> 1
Located at lib/trivial.nix:545 in <nixpkgs>
.
lib.trivial.compare
C-style comparisons
a < b, compare a b => -1 a == b, compare a b => 0 a > b, compare a b => 1
lib.trivial.splitByAndCompare
Split type into two subtypes by predicate p
, take all elements
of the first subtype to be less than all the elements of the
second subtype, compare elements of a single subtype with yes
and no
respectively.
p
Predicate
yes
Comparison function if predicate holds for both values
no
Comparison function if predicate holds for neither value
a
First value to compare
b
Second value to compare
(a -> bool) -> (a -> a -> int) -> (a -> a -> int) -> (a -> a -> int)
lib.trivial.splitByAndCompare
usage examplelet cmp = splitByAndCompare (hasPrefix "foo") compare compare; in
cmp "a" "z" => -1
cmp "fooa" "fooz" => -1
cmp "f" "a" => 1
cmp "fooa" "a" => -1
# while
compare "fooa" "a" => 1
Located at lib/trivial.nix:628 in <nixpkgs>
.
lib.trivial.importJSON
Reads a JSON file.
lib.trivial.importJSON
usage exampleexample.json
{
"title": "Example JSON",
"hello": {
"world": "foo",
"bar": {
"foobar": true
}
}
}
importJSON ./example.json
=> {
title = "Example JSON";
hello = {
world = "foo";
bar = {
foobar = true;
};
};
}
path
1. Function argument
lib.trivial.importTOML
Reads a TOML file.
lib.trivial.importTOML
usage exampleexample.toml
title = "TOML Example"
[hello]
world = "foo"
[hello.bar]
foobar = true
importTOML ./example.toml
=> {
title = "TOML Example";
hello = {
world = "foo";
bar = {
foobar = true;
};
};
}
path
1. Function argument
lib.trivial.warn
warn
message
value
Print a warning before returning the second argument.
See builtins.warn
(Nix >= 2.23).
On older versions, the Nix 2.23 behavior is emulated with builtins.trace
, including the NIX_ABORT_ON_WARN
behavior, but not the nix.conf
setting or command line option.
message
(String)Warning message to print before evaluating value
.
value
(any value)Value to return as-is.
lib.trivial.warnIf
warnIf
condition
message
value
Like warn
, but only warn when the first argument is true
.
condition
(Boolean)true
to trigger the warning before continuing with value
.
message
(String)Warning message to print before evaluating
value
(any value)Value to return as-is.
lib.trivial.warnIfNot
warnIfNot
condition
message
value
Like warnIf
, but negated: warn if the first argument is false
.
condition
false
to trigger the warning before continuing with val
.
message
Warning message to print before evaluating value
.
value
Value to return as-is.
lib.trivial.throwIfNot
Like the assert b; e
expression, but with a custom error message and
without the semicolon.
If true, return the identity function, r: r
.
If false, throw the error message.
Calls can be juxtaposed using function application, as (r: r) a = a
, so
(r: r) (r: r) a = a
, and so forth.
cond
1. Function argument
msg
2. Function argument
bool -> string -> a -> a
lib.trivial.throwIfNot
usage examplethrowIfNot (lib.isList overlays) "The overlays argument to nixpkgs must be a list."
lib.foldr (x: throwIfNot (lib.isFunction x) "All overlays passed to nixpkgs must be functions.") (r: r) overlays
pkgs
Located at lib/trivial.nix:868 in <nixpkgs>
.
lib.trivial.throwIf
Like throwIfNot, but negated (throw if the first argument is true
).
cond
1. Function argument
msg
2. Function argument
lib.trivial.checkListOfEnum
Check if the elements in a list are valid values from a enum, returning the identity function, or throwing an error message otherwise.
msg
1. Function argument
valid
2. Function argument
given
3. Function argument
String -> List ComparableVal -> List ComparableVal -> a -> a
lib.trivial.checkListOfEnum
usage examplelet colorVariants = ["bright" "dark" "black"]
in checkListOfEnum "color variants" [ "standard" "light" "dark" ] colorVariants;
=>
error: color variants: bright, black unexpected; valid ones: standard, light, dark
Located at lib/trivial.nix:929 in <nixpkgs>
.
lib.trivial.setFunctionArgs
Add metadata about expected function arguments to a function. The metadata should match the format given by builtins.functionArgs, i.e. a set from expected argument to a bool representing whether that argument has a default or not. setFunctionArgs : (a → b) → Map String Bool → (a → b)
This function is necessary because you can’t dynamically create a function of the { a, b ? foo, … }: format, but some facilities like callPackage expect to be able to query expected arguments.
lib.trivial.functionArgs
Extract the expected function arguments from a function. This works both with nix-native { a, b ? foo, … }: style functions and functions with args set with ‘setFunctionArgs’. It has the same return type and semantics as builtins.functionArgs. setFunctionArgs : (a → b) → Map String Bool.
lib.trivial.isFunction
Check whether something is a function or something annotated with function args.
lib.trivial.mirrorFunctionArgs
mirrorFunctionArgs f g
creates a new function g'
with the same behavior as g
(g' x == g x
)
but its function arguments mirroring f
(lib.functionArgs g' == lib.functionArgs f
).
f
Function to provide the argument metadata
g
Function to set the argument metadata to
mirrorFunctionArgs :: (a -> b) -> (a -> c) -> (a -> c)
lib.trivial.mirrorFunctionArgs
usage exampleaddab = {a, b}: a + b
addab { a = 2; b = 4; }
=> 6
lib.functionArgs addab
=> { a = false; b = false; }
addab1 = attrs: addab attrs + 1
addab1 { a = 2; b = 4; }
=> 7
lib.functionArgs addab1
=> { }
addab1' = lib.mirrorFunctionArgs addab addab1
addab1' { a = 2; b = 4; }
=> 7
lib.functionArgs addab1'
=> { a = false; b = false; }
Located at lib/trivial.nix:1048 in <nixpkgs>
.
lib.trivial.toFunction
Turns any non-callable values into constant functions. Returns callable values as is.
v
Any value
lib.trivial.toFunction
usage examplenix-repl> lib.toFunction 1 2
1
nix-repl> lib.toFunction (x: x + 1) 2
3
Located at lib/trivial.nix:1082 in <nixpkgs>
.
lib.trivial.fromHexString
Convert a hexadecimal string to it’s integer representation.
fromHexString :: String -> [ String ]
fromHexString "FF"
=> 255
fromHexString (builtins.hashString "sha256" "test")
=> 9223372036854775807
Located at lib/trivial.nix:1107 in <nixpkgs>
.
lib.trivial.toHexString
Convert the given positive integer to a string of its hexadecimal representation. For example:
toHexString 0 => “0”
toHexString 16 => “10”
toHexString 250 => “FA”
Located at lib/trivial.nix:1124 in <nixpkgs>
.
lib.trivial.toBaseDigits
toBaseDigits base i
converts the positive integer i to a list of its
digits in the given base. For example:
toBaseDigits 10 123 => [ 1 2 3 ]
toBaseDigits 2 6 => [ 1 1 0 ]
toBaseDigits 16 250 => [ 15 10 ]
lib.fixedPoints.fix
fix f
computes the fixed point of the given function f
. In other words, the return value is x
in x = f x
.
f
must be a lazy function.
This means that x
must be a value that can be partially evaluated,
such as an attribute set, a list, or a function.
This way, f
can use one part of x
to compute another part.
Relation to syntactic recursion
This section explains fix
by refactoring from syntactic recursion to a call of fix
instead.
For context, Nix lets you define attributes in terms of other attributes syntactically using the rec { }
syntax.
nix-repl> rec {
foo = "foo";
bar = "bar";
foobar = foo + bar;
}
{ bar = "bar"; foo = "foo"; foobar = "foobar"; }
This is convenient when constructing a value to pass to a function for example,
but an equivalent effect can be achieved with the let
binding syntax:
nix-repl> let self = {
foo = "foo";
bar = "bar";
foobar = self.foo + self.bar;
}; in self
{ bar = "bar"; foo = "foo"; foobar = "foobar"; }
But in general you can get more reuse out of let
bindings by refactoring them to a function.
nix-repl> f = self: {
foo = "foo";
bar = "bar";
foobar = self.foo + self.bar;
}
This is where fix
comes in, it contains the syntactic recursion that’s not in f
anymore.
nix-repl> fix = f:
let self = f self; in self;
By applying fix
we get the final result.
nix-repl> fix f
{ bar = "bar"; foo = "foo"; foobar = "foobar"; }
Such a refactored f
using fix
is not useful by itself.
See extends
for an example use case.
There self
is also often called final
.
f
1. Function argument
fix :: (a -> a) -> a
lib.fixedPoints.fix
usage examplefix (self: { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; })
=> { bar = "bar"; foo = "foo"; foobar = "foobar"; }
fix (self: [ 1 2 (elemAt self 0 + elemAt self 1) ])
=> [ 1 2 3 ]
Located at lib/fixed-points.nix:92 in <nixpkgs>
.
lib.fixedPoints.fix'
A variant of fix
that records the original recursive attribute set in the
result, in an attribute named __unfix__
.
This is useful in combination with the extends
function to
implement deep overriding.
lib.fixedPoints.converge
Return the fixpoint that f
converges to when called iteratively, starting
with the input x
.
nix-repl> converge (x: x / 2) 16
0
f
1. Function argument
x
2. Function argument
lib.fixedPoints.extends
Extend a function using an overlay.
Overlays allow modifying and extending fixed-point functions, specifically ones returning attribute sets. A fixed-point function is a function which is intended to be evaluated by passing the result of itself as the argument. This is possible due to Nix’s lazy evaluation.
A fixed-point function returning an attribute set has the form
final: { # attributes }
where final
refers to the lazily evaluated attribute set returned by the fixed-point function.
An overlay to such a fixed-point function has the form
final: prev: { # attributes }
where prev
refers to the result of the original function to final
, and final
is the result of the composition of the overlay and the original function.
Applying an overlay is done with extends
:
let
f = final: { # attributes };
overlay = final: prev: { # attributes };
in extends overlay f;
To get the value of final
, use lib.fix
:
let
f = final: { # attributes };
overlay = final: prev: { # attributes };
g = extends overlay f;
in fix g
The argument to the given fixed-point function after applying an overlay will not refer to its own return value, but rather to the value after evaluating the overlay function.
The given fixed-point function is called with a separate argument than if it was evaluated with lib.fix
.
Define a fixed-point function f
that expects its own output as the argument final
:
f = final: {
# Constant value a
a = 1;
# b depends on the final value of a, available as final.a
b = final.a + 2;
}
Evaluate this using lib.fix
to get the final result:
fix f
=> { a = 1; b = 3; }
An overlay represents a modification or extension of such a fixed-point function. Here’s an example of an overlay:
overlay = final: prev: {
# Modify the previous value of a, available as prev.a
a = prev.a + 10;
# Extend the attribute set with c, letting it depend on the final values of a and b
c = final.a + final.b;
}
Use extends overlay f
to apply the overlay to the fixed-point function f
.
This produces a new fixed-point function g
with the combined behavior of f
and overlay
:
g = extends overlay f
The result is a function, so we can’t print it directly, but it’s the same as:
g' = final: {
# The constant from f, but changed with the overlay
a = 1 + 10;
# Unchanged from f
b = final.a + 2;
# Extended in the overlay
c = final.a + final.b;
}
Evaluate this using lib.fix
again to get the final result:
fix g
=> { a = 11; b = 13; c = 24; }
overlay
The overlay to apply to the fixed-point function
f
The fixed-point function
extends :: (Attrs -> Attrs -> Attrs) # The overlay to apply to the fixed-point function
-> (Attrs -> Attrs) # A fixed-point function
-> (Attrs -> Attrs) # The resulting fixed-point function
lib.fixedPoints.extends
usage examplef = final: { a = 1; b = final.a + 2; }
fix f
=> { a = 1; b = 3; }
fix (extends (final: prev: { a = prev.a + 10; }) f)
=> { a = 11; b = 13; }
fix (extends (final: prev: { b = final.a + 5; }) f)
=> { a = 1; b = 6; }
fix (extends (final: prev: { c = final.a + final.b; }) f)
=> { a = 1; b = 3; c = 4; }
Located at lib/fixed-points.nix:307 in <nixpkgs>
.
lib.fixedPoints.composeExtensions
Compose two overlay functions and return a single overlay function that combines them. For more details see: composeManyExtensions.
Located at lib/fixed-points.nix:322 in <nixpkgs>
.
lib.fixedPoints.composeManyExtensions
Composes a list of overlays
and returns a single overlay function that combines them.
The result is produced by using the update operator //
.
This means nested values of previous overlays are not merged recursively.
In other words, previously defined attributes are replaced, ignoring the previous value, unless referenced by the overlay; for example final: prev: { foo = final.foo + 1; }
.
extensions
A list of overlay functions
The order of the overlays in the list is important.
Each overlay function takes two arguments, by convention final
and prev
, and returns an attribute set.
final
is the result of the fixed-point function, with all overlays applied.
prev
is the result of the previous overlay function(s).
# Pseudo code
let
# final prev
# ↓ ↓
OverlayFn = { ... } -> { ... } -> { ... };
in
composeManyExtensions :: ListOf OverlayFn -> OverlayFn
lib.fixedPoints.composeManyExtensions
usage examplelet
# The "original function" that is extended by the overlays.
# Note that it doesn't have prev: as argument since no overlay function precedes it.
original = final: { a = 1; };
# Each overlay function has 'final' and 'prev' as arguments.
overlayA = final: prev: { b = final.c; c = 3; };
overlayB = final: prev: { c = 10; x = prev.c or 5; };
extensions = composeManyExtensions [ overlayA overlayB ];
# Caluculate the fixed point of all composed overlays.
fixedpoint = lib.fix (lib.extends extensions original );
in fixedpoint
=>
{
a = 1;
b = 10;
c = 10;
x = 3;
}
Located at lib/fixed-points.nix:394 in <nixpkgs>
.
lib.fixedPoints.makeExtensible
Create an overridable, recursive attribute set. For example:
nix-repl> obj = makeExtensible (final: { })
nix-repl> obj
{ __unfix__ = «lambda»; extend = «lambda»; }
nix-repl> obj = obj.extend (final: prev: { foo = "foo"; })
nix-repl> obj
{ __unfix__ = «lambda»; extend = «lambda»; foo = "foo"; }
nix-repl> obj = obj.extend (final: prev: { foo = prev.foo + " + "; bar = "bar"; foobar = final.foo + final.bar; })
nix-repl> obj
{ __unfix__ = «lambda»; bar = "bar"; extend = «lambda»; foo = "foo + "; foobar = "foo + bar"; }
Located at lib/fixed-points.nix:416 in <nixpkgs>
.
lib.fixedPoints.makeExtensibleWithCustomName
Same as makeExtensible
but the name of the extending attribute is
customized.
extenderName
1. Function argument
rattrs
2. Function argument
Located at lib/fixed-points.nix:432 in <nixpkgs>
.
lib.fixedPoints.toExtension
Convert to an extending function (overlay).
toExtension
is the toFunction
for extending functions (a.k.a. extensions or overlays).
It converts a non-function or a single-argument function to an extending function,
while returning a two-argument function as-is.
That is, it takes a value of the shape x
, prev: x
, or final: prev: x
,
and returns final: prev: x
, assuming x
is not a function.
This function takes care of the input to stdenv.mkDerivation
’s
overrideAttrs
function.
It bridges the gap between <pkg>.overrideAttrs
before and after the overlay-style support.
f
The function or value to convert to an extending function.
toExtension ::
b' -> Any -> Any -> b'
or
toExtension ::
(a -> b') -> Any -> a -> b'
or
toExtension ::
(a -> a -> b) -> a -> a -> b
where b' = ! Callable
Set a = b = b' = AttrSet & ! Callable to make toExtension return an extending function.
lib.fixedPoints.toExtension
usage examplefix (final: { a = 0; c = final.a; })
=> { a = 0; c = 0; };
fix (extends (toExtension { a = 1; b = 2; }) (final: { a = 0; c = final.a; }))
=> { a = 1; b = 2; c = 1; };
fix (extends (toExtension (prev: { a = 1; b = prev.a; })) (final: { a = 0; c = final.a; }))
=> { a = 1; b = 0; c = 1; };
fix (extends (toExtension (final: prev: { a = 1; b = prev.a; c = final.a + 1 })) (final: { a = 0; c = final.a; }))
=> { a = 1; b = 0; c = 2; };
Located at lib/fixed-points.nix:497 in <nixpkgs>
.
General list operations.
lib.lists.singleton
Create a list consisting of a single element. singleton x
is
sometimes more convenient with respect to indentation than [x]
when x spans multiple lines.
x
1. Function argument
singleton :: a -> [a]
lib.lists.singleton
usage examplesingleton "foo"
=> [ "foo" ]
Located at lib/lists.nix:42 in <nixpkgs>
.
lib.lists.forEach
Apply the function to each element in the list.
Same as map
, but arguments flipped.
xs
1. Function argument
f
2. Function argument
forEach :: [a] -> (a -> b) -> [b]
lib.lists.forEach
usage exampleforEach [ 1 2 ] (x:
toString x
)
=> [ "1" "2" ]
Located at lib/lists.nix:77 in <nixpkgs>
.
lib.lists.foldr
“right fold” a binary function op
between successive elements of
list
with nul
as the starting value, i.e.,
foldr op nul [x_1 x_2 ... x_n] == op x_1 (op x_2 ... (op x_n nul))
.
op
1. Function argument
nul
2. Function argument
list
3. Function argument
foldr :: (a -> b -> b) -> b -> [a] -> b
lib.lists.foldr
usage exampleconcat = foldr (a: b: a + b) "z"
concat [ "a" "b" "c" ]
=> "abcz"
# different types
strange = foldr (int: str: toString (int + 1) + str) "a"
strange [ 1 2 3 4 ]
=> "2345a"
Located at lib/lists.nix:121 in <nixpkgs>
.
lib.lists.fold
fold
is an alias of foldr
for historic reasons
Located at lib/lists.nix:134 in <nixpkgs>
.
lib.lists.foldl
“left fold”, like foldr
, but from the left:
foldl op nul [x_1 x_2 ... x_n] == op (... (op (op nul x_1) x_2) ... x_n)
.
op
1. Function argument
nul
2. Function argument
list
3. Function argument
foldl :: (b -> a -> b) -> b -> [a] -> b
lib.lists.foldl
usage examplelconcat = foldl (a: b: a + b) "z"
lconcat [ "a" "b" "c" ]
=> "zabc"
# different types
lstrange = foldl (str: int: str + toString (int + 1)) "a"
lstrange [ 1 2 3 4 ]
=> "a2345"
Located at lib/lists.nix:178 in <nixpkgs>
.
lib.lists.foldl'
Reduce a list by applying a binary operator from left to right, starting with an initial accumulator.
Before each application of the operator, the accumulator value is evaluated.
This behavior makes this function stricter than foldl
.
Unlike builtins.foldl'
,
the initial accumulator argument is evaluated before the first iteration.
A call like
foldl' op acc₀ [ x₀ x₁ x₂ ... xₙ₋₁ xₙ ]
is (denotationally) equivalent to the following,
but with the added benefit that foldl'
itself will never overflow the stack.
let
acc₁ = builtins.seq acc₀ (op acc₀ x₀ );
acc₂ = builtins.seq acc₁ (op acc₁ x₁ );
acc₃ = builtins.seq acc₂ (op acc₂ x₂ );
...
accₙ = builtins.seq accₙ₋₁ (op accₙ₋₁ xₙ₋₁);
accₙ₊₁ = builtins.seq accₙ (op accₙ xₙ );
in
accₙ₊₁
# Or ignoring builtins.seq
op (op (... (op (op (op acc₀ x₀) x₁) x₂) ...) xₙ₋₁) xₙ
op
The binary operation to run, where the two arguments are:
acc
: The current accumulator value: Either the initial one for the first iteration, or the result of the previous iteration
x
: The corresponding list element for this iteration
acc
The initial accumulator value.
The accumulator value is evaluated in any case before the first iteration starts.
To avoid evaluation even before the list
argument is given an eta expansion can be used:
list: lib.foldl' op acc list
list
The list to fold
foldl' :: (acc -> x -> acc) -> acc -> [x] -> acc
lib.lists.foldl'
usage examplefoldl' (acc: x: acc + x) 0 [1 2 3]
=> 6
Located at lib/lists.nix:262 in <nixpkgs>
.
lib.lists.imap0
Map with index starting from 0
f
1. Function argument
list
2. Function argument
imap0 :: (int -> a -> b) -> [a] -> [b]
lib.lists.imap0
usage exampleimap0 (i: v: "${v}-${toString i}") ["a" "b"]
=> [ "a-0" "b-1" ]
Located at lib/lists.nix:301 in <nixpkgs>
.
lib.lists.imap1
Map with index starting from 1
f
1. Function argument
list
2. Function argument
imap1 :: (int -> a -> b) -> [a] -> [b]
lib.lists.imap1
usage exampleimap1 (i: v: "${v}-${toString i}") ["a" "b"]
=> [ "a-1" "b-2" ]
Located at lib/lists.nix:334 in <nixpkgs>
.
lib.lists.ifilter0
Filter a list for elements that satisfy a predicate function.
The predicate function is called with both the index and value for each element.
It must return true
/false
to include/exclude a given element in the result.
This function is strict in the result of the predicate function for each element.
This function has O(n) complexity.
Also see builtins.filter
(available as lib.lists.filter
),
which can be used instead when the index isn’t needed.
ipred
The predicate function, it takes two arguments:
(int): the index of the element.
(a): the value of the element.
It must return true
/false
to include/exclude a given element from the result.
list
The list to filter using the predicate.
ifilter0 :: (int -> a -> bool) -> [a] -> [a]
lib.lists.ifilter0
usage exampleifilter0 (i: v: i == 0 || v > 2) [ 1 2 3 ]
=> [ 1 3 ]
Located at lib/lists.nix:375 in <nixpkgs>
.
lib.lists.concatMap
Map and concatenate the result.
concatMap :: (a -> [b]) -> [a] -> [b]
lib.lists.concatMap
usage exampleconcatMap (x: [x] ++ ["z"]) ["a" "b"]
=> [ "a" "z" "b" "z" ]
Located at lib/lists.nix:404 in <nixpkgs>
.
lib.lists.flatten
Flatten the argument into a single list; that is, nested lists are spliced into the top-level lists.
x
1. Function argument
lib.lists.flatten
usage exampleflatten [1 [2 [3] 4] 5]
=> [1 2 3 4 5]
flatten 1
=> [1]
Located at lib/lists.nix:431 in <nixpkgs>
.
lib.lists.remove
Remove elements equal to ‘e’ from a list. Useful for buildInputs.
e
Element to remove from list
list
The list
remove :: a -> [a] -> [a]
lib.lists.remove
usage exampleremove 3 [ 1 3 4 3 ]
=> [ 1 4 ]
Located at lib/lists.nix:467 in <nixpkgs>
.
lib.lists.findSingle
Find the sole element in the list matching the specified predicate.
Returns default
if no such element exists, or
multiple
if there are multiple matching elements.
pred
Predicate
default
Default value to return if element was not found.
multiple
Default value to return if more than one element was found
list
Input list
findSingle :: (a -> bool) -> a -> a -> [a] -> a
lib.lists.findSingle
usage examplefindSingle (x: x == 3) "none" "multiple" [ 1 3 3 ]
=> "multiple"
findSingle (x: x == 3) "none" "multiple" [ 1 3 ]
=> 3
findSingle (x: x == 3) "none" "multiple" [ 1 9 ]
=> "none"
Located at lib/lists.nix:517 in <nixpkgs>
.
lib.lists.findFirstIndex
Find the first index in the list matching the specified
predicate or return default
if no such element exists.
pred
Predicate
default
Default value to return
list
Input list
findFirstIndex :: (a -> Bool) -> b -> [a] -> (Int | b)
lib.lists.findFirstIndex
usage examplefindFirstIndex (x: x > 3) null [ 0 6 4 ]
=> 1
findFirstIndex (x: x > 9) null [ 0 6 4 ]
=> null
Located at lib/lists.nix:564 in <nixpkgs>
.
lib.lists.findFirst
Find the first element in the list matching the specified
predicate or return default
if no such element exists.
pred
Predicate
default
Default value to return
list
Input list
findFirst :: (a -> bool) -> a -> [a] -> a
lib.lists.findFirst
usage examplefindFirst (x: x > 3) 7 [ 1 6 4 ]
=> 6
findFirst (x: x > 9) 7 [ 1 6 4 ]
=> 7
Located at lib/lists.nix:638 in <nixpkgs>
.
lib.lists.any
Return true if function pred
returns true for at least one
element of list
.
pred
Predicate
list
Input list
any :: (a -> bool) -> [a] -> bool
lib.lists.any
usage exampleany isString [ 1 "a" { } ]
=> true
any isString [ 1 { } ]
=> false
Located at lib/lists.nix:683 in <nixpkgs>
.
lib.lists.all
Return true if function pred
returns true for all elements of
list
.
pred
Predicate
list
Input list
all :: (a -> bool) -> [a] -> bool
lib.lists.all
usage exampleall (x: x < 3) [ 1 2 ]
=> true
all (x: x < 3) [ 1 2 3 ]
=> false
Located at lib/lists.nix:718 in <nixpkgs>
.
lib.lists.count
Count how many elements of list
match the supplied predicate
function.
pred
Predicate
count :: (a -> bool) -> [a] -> int
lib.lists.count
usage examplecount (x: x == 3) [ 3 2 3 4 6 ]
=> 2
Located at lib/lists.nix:747 in <nixpkgs>
.
lib.lists.optional
Return a singleton list or an empty list, depending on a boolean
value. Useful when building lists with optional elements
(e.g. ++ optional (system == "i686-linux") firefox
).
cond
1. Function argument
elem
2. Function argument
optional :: bool -> a -> [a]
lib.lists.optional
usage exampleoptional true "foo"
=> [ "foo" ]
optional false "foo"
=> [ ]
Located at lib/lists.nix:784 in <nixpkgs>
.
lib.lists.optionals
Return a list or an empty list, depending on a boolean value.
cond
Condition
elems
List to return if condition is true
optionals :: bool -> [a] -> [a]
lib.lists.optionals
usage exampleoptionals true [ 2 3 ]
=> [ 2 3 ]
optionals false [ 2 3 ]
=> [ ]
Located at lib/lists.nix:818 in <nixpkgs>
.
lib.lists.toList
If argument is a list, return it; else, wrap it in a singleton list. If you’re using this, you should almost certainly reconsider if there isn’t a more “well-typed” approach.
x
1. Function argument
lib.lists.toList
usage exampletoList [ 1 2 ]
=> [ 1 2 ]
toList "hi"
=> [ "hi "]
Located at lib/lists.nix:847 in <nixpkgs>
.
lib.lists.range
Return a list of integers from first
up to and including last
.
first
First integer in the range
last
Last integer in the range
range :: int -> int -> [int]
lib.lists.range
usage examplerange 2 4
=> [ 2 3 4 ]
range 3 2
=> [ ]
Located at lib/lists.nix:881 in <nixpkgs>
.
lib.lists.replicate
Return a list with n
copies of an element.
n
1. Function argument
elem
2. Function argument
replicate :: int -> a -> [a]
lib.lists.replicate
usage examplereplicate 3 "a"
=> [ "a" "a" "a" ]
replicate 2 true
=> [ true true ]
Located at lib/lists.nix:921 in <nixpkgs>
.
lib.lists.partition
Splits the elements of a list in two lists, right
and
wrong
, depending on the evaluation of a predicate.
pred
Predicate
list
Input list
(a -> bool) -> [a] -> { right :: [a]; wrong :: [a]; }
lib.lists.partition
usage examplepartition (x: x > 2) [ 5 1 2 3 4 ]
=> { right = [ 5 3 4 ]; wrong = [ 1 2 ]; }
Located at lib/lists.nix:954 in <nixpkgs>
.
lib.lists.groupBy'
Splits the elements of a list into many lists, using the return value of a predicate.
Predicate should return a string which becomes keys of attrset groupBy
returns.
groupBy'
allows to customise the combining function and initial value
op
1. Function argument
nul
2. Function argument
pred
3. Function argument
lst
4. Function argument
lib.lists.groupBy'
usage examplegroupBy (x: boolToString (x > 2)) [ 5 1 2 3 4 ]
=> { true = [ 5 3 4 ]; false = [ 1 2 ]; }
groupBy (x: x.name) [ {name = "icewm"; script = "icewm &";}
{name = "xfce"; script = "xfce4-session &";}
{name = "icewm"; script = "icewmbg &";}
{name = "mate"; script = "gnome-session &";}
]
=> { icewm = [ { name = "icewm"; script = "icewm &"; }
{ name = "icewm"; script = "icewmbg &"; } ];
mate = [ { name = "mate"; script = "gnome-session &"; } ];
xfce = [ { name = "xfce"; script = "xfce4-session &"; } ];
}
groupBy' builtins.add 0 (x: boolToString (x > 2)) [ 5 1 2 3 4 ]
=> { true = 12; false = 3; }
Located at lib/lists.nix:1004 in <nixpkgs>
.
lib.lists.zipListsWith
Merges two lists of the same size together. If the sizes aren’t the same the merging stops at the shortest. How both lists are merged is defined by the first argument.
f
Function to zip elements of both lists
fst
First list
snd
Second list
zipListsWith :: (a -> b -> c) -> [a] -> [b] -> [c]
lib.lists.zipListsWith
usage examplezipListsWith (a: b: a + b) ["h" "l"] ["e" "o"]
=> ["he" "lo"]
Located at lib/lists.nix:1050 in <nixpkgs>
.
lib.lists.zipLists
Merges two lists of the same size together. If the sizes aren’t the same the merging stops at the shortest.
fst
First list
snd
Second list
zipLists :: [a] -> [b] -> [{ fst :: a; snd :: b; }]
lib.lists.zipLists
usage examplezipLists [ 1 2 ] [ "a" "b" ]
=> [ { fst = 1; snd = "a"; } { fst = 2; snd = "b"; } ]
Located at lib/lists.nix:1088 in <nixpkgs>
.
lib.lists.reverseList
Reverse the order of the elements of a list.
xs
1. Function argument
reverseList :: [a] -> [a]
lib.lists.reverseList
usage examplereverseList [ "b" "o" "j" ]
=> [ "j" "o" "b" ]
Located at lib/lists.nix:1116 in <nixpkgs>
.
lib.lists.listDfs
Depth-First Search (DFS) for lists list != []
.
before a b == true
means that b
depends on a
(there’s an
edge from b
to a
).
stopOnCycles
1. Function argument
before
2. Function argument
list
3. Function argument
lib.lists.listDfs
usage examplelistDfs true hasPrefix [ "/home/user" "other" "/" "/home" ]
== { minimal = "/"; # minimal element
visited = [ "/home/user" ]; # seen elements (in reverse order)
rest = [ "/home" "other" ]; # everything else
}
listDfs true hasPrefix [ "/home/user" "other" "/" "/home" "/" ]
== { cycle = "/"; # cycle encountered at this element
loops = [ "/" ]; # and continues to these elements
visited = [ "/" "/home/user" ]; # elements leading to the cycle (in reverse order)
rest = [ "/home" "other" ]; # everything else
Located at lib/lists.nix:1161 in <nixpkgs>
.
lib.lists.toposort
Sort a list based on a partial ordering using DFS. This
implementation is O(N^2), if your ordering is linear, use sort
instead.
before a b == true
means that b
should be after a
in the result.
before
1. Function argument
list
2. Function argument
lib.lists.toposort
usage exampletoposort hasPrefix [ "/home/user" "other" "/" "/home" ]
== { result = [ "/" "/home" "/home/user" "other" ]; }
toposort hasPrefix [ "/home/user" "other" "/" "/home" "/" ]
== { cycle = [ "/home/user" "/" "/" ]; # path leading to a cycle
loops = [ "/" ]; } # loops back to these elements
toposort hasPrefix [ "other" "/home/user" "/home" "/" ]
== { result = [ "other" "/" "/home" "/home/user" ]; }
toposort (a: b: a < b) [ 3 2 1 ] == { result = [ 1 2 3 ]; }
Located at lib/lists.nix:1218 in <nixpkgs>
.
lib.lists.sort
Sort a list based on a comparator function which compares two elements and returns true if the first argument is strictly below the second argument. The returned list is sorted in an increasing order. The implementation does a quick-sort.
See also sortOn
, which applies the
default comparison on a function-derived property, and may be more efficient.
comparator
1. Function argument
list
2. Function argument
sort :: (a -> a -> Bool) -> [a] -> [a]
lib.lists.sort
usage examplesort (p: q: p < q) [ 5 3 7 ]
=> [ 3 5 7 ]
Located at lib/lists.nix:1273 in <nixpkgs>
.
lib.lists.sortOn
Sort a list based on the default comparison of a derived property b
.
The items are returned in b
-increasing order.
Performance:
The passed function f
is only evaluated once per item,
unlike an unprepared sort
using
f p < f q
.
Laws:
sortOn f == sort (p: q: f p < f q)
f
1. Function argument
list
2. Function argument
sortOn :: (a -> b) -> [a] -> [a], for comparable b
lib.lists.sortOn
usage examplesortOn stringLength [ "aa" "b" "cccc" ]
=> [ "b" "aa" "cccc" ]
Located at lib/lists.nix:1319 in <nixpkgs>
.
lib.lists.compareLists
Compare two lists element-by-element.
cmp
1. Function argument
a
2. Function argument
b
3. Function argument
lib.lists.compareLists
usage examplecompareLists compare [] []
=> 0
compareLists compare [] [ "a" ]
=> -1
compareLists compare [ "a" ] []
=> 1
compareLists compare [ "a" "b" ] [ "a" "c" ]
=> -1
Located at lib/lists.nix:1367 in <nixpkgs>
.
lib.lists.naturalSort
Sort list using “Natural sorting”. Numeric portions of strings are sorted in numeric order.
lst
1. Function argument
lib.lists.naturalSort
usage examplenaturalSort ["disk11" "disk8" "disk100" "disk9"]
=> ["disk8" "disk9" "disk11" "disk100"]
naturalSort ["10.46.133.149" "10.5.16.62" "10.54.16.25"]
=> ["10.5.16.62" "10.46.133.149" "10.54.16.25"]
naturalSort ["v0.2" "v0.15" "v0.0.9"]
=> [ "v0.0.9" "v0.2" "v0.15" ]
Located at lib/lists.nix:1406 in <nixpkgs>
.
lib.lists.take
Return the first (at most) N elements of a list.
count
Number of elements to take
list
Input list
take :: int -> [a] -> [a]
lib.lists.take
usage exampletake 2 [ "a" "b" "c" "d" ]
=> [ "a" "b" ]
take 2 [ ]
=> [ ]
Located at lib/lists.nix:1447 in <nixpkgs>
.
lib.lists.drop
Remove the first (at most) N elements of a list.
count
Number of elements to drop
list
Input list
drop :: int -> [a] -> [a]
lib.lists.drop
usage exampledrop 2 [ "a" "b" "c" "d" ]
=> [ "c" "d" ]
drop 2 [ ]
=> [ ]
Located at lib/lists.nix:1483 in <nixpkgs>
.
lib.lists.hasPrefix
Whether the first list is a prefix of the second list.
list1
1. Function argument
list2
2. Function argument
hasPrefix :: [a] -> [a] -> bool
lib.lists.hasPrefix
usage examplehasPrefix [ 1 2 ] [ 1 2 3 4 ]
=> true
hasPrefix [ 0 1 ] [ 1 2 3 4 ]
=> false
Located at lib/lists.nix:1520 in <nixpkgs>
.
lib.lists.removePrefix
Remove the first list as a prefix from the second list. Error if the first list isn’t a prefix of the second list.
list1
1. Function argument
list2
2. Function argument
removePrefix :: [a] -> [a] -> [a]
lib.lists.removePrefix
usage exampleremovePrefix [ 1 2 ] [ 1 2 3 4 ]
=> [ 3 4 ]
removePrefix [ 0 1 ] [ 1 2 3 4 ]
=> <error>
Located at lib/lists.nix:1558 in <nixpkgs>
.
lib.lists.sublist
Return a list consisting of at most count
elements of list
,
starting at index start
.
start
Index at which to start the sublist
count
Number of elements to take
list
Input list
sublist :: int -> int -> [a] -> [a]
lib.lists.sublist
usage examplesublist 1 3 [ "a" "b" "c" "d" "e" ]
=> [ "b" "c" "d" ]
sublist 1 3 [ ]
=> [ ]
Located at lib/lists.nix:1603 in <nixpkgs>
.
lib.lists.commonPrefix
The common prefix of two lists.
list1
1. Function argument
list2
2. Function argument
commonPrefix :: [a] -> [a] -> [a]
lib.lists.commonPrefix
usage examplecommonPrefix [ 1 2 3 4 5 6 ] [ 1 2 4 8 ]
=> [ 1 2 ]
commonPrefix [ 1 2 3 ] [ 1 2 3 4 5 ]
=> [ 1 2 3 ]
commonPrefix [ 1 2 3 ] [ 4 5 6 ]
=> [ ]
Located at lib/lists.nix:1649 in <nixpkgs>
.
lib.lists.last
Return the last element of a list.
This function throws an error if the list is empty.
list
1. Function argument
last :: [a] -> a
lib.lists.last
usage examplelast [ 1 2 3 ]
=> 3
Located at lib/lists.nix:1692 in <nixpkgs>
.
lib.lists.init
Return all elements but the last.
This function throws an error if the list is empty.
list
1. Function argument
init :: [a] -> [a]
lib.lists.init
usage exampleinit [ 1 2 3 ]
=> [ 1 2 ]
Located at lib/lists.nix:1725 in <nixpkgs>
.
lib.lists.crossLists
Return the image of the cross product of some lists by a function.
lib.lists.crossLists
usage examplecrossLists (x: y: "${toString x}${toString y}") [[1 2] [3 4]]
=> [ "13" "14" "23" "24" ]
The following function call is equivalent to the one deprecated above:
mapCartesianProduct (x: "${toString x.a}${toString x.b}") { a = [1 2]; b = [3 4]; }
=> [ "13" "14" "23" "24" ]
Located at lib/lists.nix:1751 in <nixpkgs>
.
lib.lists.unique
Remove duplicate elements from the list
. O(n^2) complexity.
list
Input list
unique :: [a] -> [a]
lib.lists.unique
usage exampleunique [ 3 2 3 4 ]
=> [ 3 2 4 ]
Located at lib/lists.nix:1793 in <nixpkgs>
.
lib.lists.allUnique
Check if list contains only unique elements. O(n^2) complexity.
list
1. Function argument
allUnique :: [a] -> bool
lib.lists.allUnique
usage exampleallUnique [ 3 2 3 4 ]
=> false
allUnique [ 3 2 4 1 ]
=> true
Located at lib/lists.nix:1824 in <nixpkgs>
.
lib.lists.intersectLists
Intersects list ‘list1’ and another list (list2
).
O(nm) complexity.
list1
First list
list2
Second list
lib.lists.intersectLists
usage exampleintersectLists [ 1 2 3 ] [ 6 3 2 ]
=> [ 3 2 ]
Located at lib/lists.nix:1854 in <nixpkgs>
.
lib.lists.subtractLists
Subtracts list ‘e’ from another list (list2
).
O(nm) complexity.
e
First list
list2
Second list
lib.lists.subtractLists
usage examplesubtractLists [ 3 2 ] [ 1 2 3 4 5 3 ]
=> [ 1 4 5 ]
Located at lib/lists.nix:1883 in <nixpkgs>
.
lib.lists.mutuallyExclusive
Test if two lists have no common element. It should be slightly more efficient than (intersectLists a b == [])
Collection of functions useful for debugging broken nix expressions.
trace
-like functions take two values, print
the first to stderr and return the second.
traceVal
-like functions take one argument
which both printed and returned.
traceSeq
-like functions fully evaluate their
traced value before printing (not just to “weak
head normal form” like trace does by default).
Functions that end in -Fn
take an additional
function as their first argument, which is applied
to the traced value before it is printed.
lib.debug.traceIf
Conditionally trace the supplied message, based on a predicate.
pred
Predicate to check
msg
Message that should be traced
x
Value to return
traceIf :: bool -> string -> a -> a
lib.debug.traceIf
usage exampletraceIf true "hello" 3
trace: hello
=> 3
Located at lib/debug.nix:72 in <nixpkgs>
.
lib.debug.traceValFn
Trace the supplied value after applying a function to it, and return the original value.
f
Function to apply
x
Value to trace and return
traceValFn :: (a -> b) -> a -> a
lib.debug.traceValFn
usage exampletraceValFn (v: "mystring ${v}") "foo"
trace: mystring foo
=> "foo"
Located at lib/debug.nix:110 in <nixpkgs>
.
lib.debug.traceVal
Trace the supplied value and return it.
x
Value to trace and return
traceVal :: a -> a
lib.debug.traceVal
usage exampletraceVal 42
# trace: 42
=> 42
Located at lib/debug.nix:141 in <nixpkgs>
.
lib.debug.traceSeq
builtins.trace
, but the value is builtins.deepSeq
ed first.
x
The value to trace
y
The value to return
traceSeq :: a -> b -> b
lib.debug.traceSeq
usage exampletrace { a.b.c = 3; } null
trace: { a = <CODE>; }
=> null
traceSeq { a.b.c = 3; } null
trace: { a = { b = { c = 3; }; }; }
=> null
Located at lib/debug.nix:178 in <nixpkgs>
.
lib.debug.traceSeqN
Like traceSeq
, but only evaluate down to depth n.
This is very useful because lots of traceSeq
usages
lead to an infinite recursion.
depth
1. Function argument
x
2. Function argument
y
3. Function argument
traceSeqN :: Int -> a -> b -> b
lib.debug.traceSeqN
usage exampletraceSeqN 2 { a.b.c = 3; } null
trace: { a = { b = {…}; }; }
=> null
Located at lib/debug.nix:220 in <nixpkgs>
.
lib.debug.traceValSeqFn
A combination of traceVal
and traceSeq
that applies a
provided function to the value to be traced after deepSeq
ing
it.
lib.debug.traceValSeq
A combination of traceVal
and traceSeq
.
lib.debug.traceValSeqNFn
A combination of traceVal
and traceSeqN
that applies a
provided function to the value to be traced.
f
Function to apply
depth
2. Function argument
v
Value to trace
Located at lib/debug.nix:284 in <nixpkgs>
.
lib.debug.traceValSeqN
A combination of traceVal
and traceSeqN
.
lib.debug.traceFnSeqN
Trace the input and output of a function f
named name
,
both down to depth
.
This is useful for adding around a function call, to see the before/after of values as they are transformed.
depth
1. Function argument
name
2. Function argument
f
3. Function argument
v
4. Function argument
lib.debug.traceFnSeqN
usage exampletraceFnSeqN 2 "id" (x: x) { a.b.c = 3; }
trace: { fn = "id"; from = { a.b = {…}; }; to = { a.b = {…}; }; }
=> { a.b.c = 3; }
Located at lib/debug.nix:343 in <nixpkgs>
.
lib.debug.runTests
Evaluates a set of tests.
A test is an attribute set {expr, expected}
,
denoting an expression and its expected result.
The result is a list
of failed tests, each represented as
{name, expected, result}
,
expected
What was passed as expected
result
The actual result
of the test
Used for regression testing of the functions in lib; see tests.nix for more examples.
Important: Only attributes that start with test
are executed.
If you want to run only a subset of the tests add the attribute tests = ["testName"];
tests
Tests to run
runTests :: {
tests = [ String ];
${testName} :: {
expr :: a;
expected :: a;
};
}
->
[
{
name :: String;
expected :: a;
result :: a;
}
]
lib.debug.runTests
usage examplerunTests {
testAndOk = {
expr = lib.and true false;
expected = false;
};
testAndFail = {
expr = lib.and true false;
expected = true;
};
}
->
[
{
name = "testAndFail";
expected = true;
result = false;
}
]
Located at lib/debug.nix:432 in <nixpkgs>
.
lib.debug.testAllTrue
Create a test assuming that list elements are true
.
expr
1. Function argument
lib.debug.testAllTrue
usage example{ testX = allTrue [ true ]; }
Located at lib/debug.nix:463 in <nixpkgs>
.
Nixpkgs/NixOS option handling.
lib.options.isOption
Type: isOption :: a -> bool
Returns true when the given argument is an option
lib.options.isOption
usage exampleisOption 1 // => false
isOption (mkOption {}) // => true
Located at lib/options.nix:56 in <nixpkgs>
.
lib.options.mkOption
Creates an Option attribute set. mkOption accepts an attribute set with the following keys:
All keys default to null
when not given.
default
Default value used when no definition is given in the configuration.
defaultText
Textual representation of the default, for the manual.
example
Example value used in the manual.
description
String describing the option.
relatedPackages
Related packages used in the manual (see genRelatedPackages
in …/nixos/lib/make-options-doc/default.nix).
type
Option type, providing type-checking and value merging.
apply
Function that converts the option value to something else.
internal
Whether the option is for NixOS developers only.
visible
Whether the option shows up in the manual. Default: true. Use false to hide the option and any sub-options from submodules. Use “shallow” to hide only sub-options.
readOnly
Whether the option can be set only once
lib.options.mkOption
usage examplemkOption { } // => { _type = "option"; }
mkOption { default = "foo"; } // => { _type = "option"; default = "foo"; }
Located at lib/options.nix:66 in <nixpkgs>
.
lib.options.mkEnableOption
Creates an Option attribute set for a boolean value option i.e an option to be toggled on or off:
name
Name for the created option
lib.options.mkEnableOption
usage examplemkEnableOption "foo"
=> { _type = "option"; default = false; description = "Whether to enable foo."; example = true; type = { ... }; }
Located at lib/options.nix:98 in <nixpkgs>
.
lib.options.mkPackageOption
Type: mkPackageOption :: pkgs -> (string|[string]) -> { nullable? :: bool, default? :: string|[string], example? :: null|string|[string], extraDescription? :: string, pkgsText? :: string } -> option
Creates an Option attribute set for an option that specifies the package a module should use for some purpose.
The package is specified in the third argument under default
as a list of strings
representing its attribute path in nixpkgs (or another package set).
Because of this, you need to pass nixpkgs itself (usually pkgs
in a module;
alternatively to nixpkgs itself, another package set) as the first argument.
If you pass another package set you should set the pkgsText
option.
This option is used to display the expression for the package set. It is "pkgs"
by default.
If your expression is complex you should parenthesize it, as the pkgsText
argument
is usually immediately followed by an attribute lookup (.
).
The second argument may be either a string or a list of strings.
It provides the display name of the package in the description of the generated option
(using only the last element if the passed value is a list)
and serves as the fallback value for the default
argument.
To include extra information in the description, pass extraDescription
to
append arbitrary text to the generated description.
You can also pass an example
value, either a literal string or an attribute path.
The default
argument can be omitted if the provided name is
an attribute of pkgs (if name
is a string) or a valid attribute path in pkgs (if name
is a list).
You can also set default
to just a string in which case it is interpreted as an attribute name
(a singleton attribute path, if you will).
If you wish to explicitly provide no default, pass null
as default
.
If you want users to be able to set no package, pass nullable = true
.
In this mode a default = null
will not be interpreted as no default and is interpreted literally.
pkgs
Package set (an instantiation of nixpkgs such as pkgs in modules or another package set)
name
Name for the package, shown in option description
nullable
Whether the package can be null, for example to disable installing a package altogether (defaults to false)
default
The attribute path where the default package is located (may be omitted, in which case it is copied from name
)
example
A string or an attribute path to use as an example (may be omitted)
extraDescription
Additional text to include in the option description (may be omitted)
pkgsText
Representation of the package set passed as pkgs (defaults to "pkgs"
)
lib.options.mkPackageOption
usage examplemkPackageOption pkgs "hello" { }
=> { ...; default = pkgs.hello; defaultText = literalExpression "pkgs.hello"; description = "The hello package to use."; type = package; }
mkPackageOption pkgs "GHC" {
default = [ "ghc" ];
example = "pkgs.haskell.packages.ghc92.ghc.withPackages (hkgs: [ hkgs.primes ])";
}
=> { ...; default = pkgs.ghc; defaultText = literalExpression "pkgs.ghc"; description = "The GHC package to use."; example = literalExpression "pkgs.haskell.packages.ghc92.ghc.withPackages (hkgs: [ hkgs.primes ])"; type = package; }
mkPackageOption pkgs [ "python3Packages" "pytorch" ] {
extraDescription = "This is an example and doesn't actually do anything.";
}
=> { ...; default = pkgs.python3Packages.pytorch; defaultText = literalExpression "pkgs.python3Packages.pytorch"; description = "The pytorch package to use. This is an example and doesn't actually do anything."; type = package; }
mkPackageOption pkgs "nushell" {
nullable = true;
}
=> { ...; default = pkgs.nushell; defaultText = literalExpression "pkgs.nushell"; description = "The nushell package to use."; type = nullOr package; }
mkPackageOption pkgs "coreutils" {
default = null;
}
=> { ...; description = "The coreutils package to use."; type = package; }
mkPackageOption pkgs "dbus" {
nullable = true;
default = null;
}
=> { ...; default = null; description = "The dbus package to use."; type = nullOr package; }
mkPackageOption pkgs.javaPackages "OpenJFX" {
default = "openjfx20";
pkgsText = "pkgs.javaPackages";
}
=> { ...; default = pkgs.javaPackages.openjfx20; defaultText = literalExpression "pkgs.javaPackages.openjfx20"; description = "The OpenJFX package to use."; type = package; }
Located at lib/options.nix:185 in <nixpkgs>
.
lib.options.mkPackageOptionMD
Deprecated alias of mkPackageOption, to be removed in 25.05. Previously used to create options with markdown documentation, which is no longer required.
Located at lib/options.nix:226 in <nixpkgs>
.
lib.options.mkSinkUndeclaredOptions
This option accepts anything, but it does not produce any result.
This is useful for sharing a module across different module sets without having to implement similar features as long as the values of the options are not accessed.
attrs
Function argument
Located at lib/options.nix:233 in <nixpkgs>
.
lib.options.mergeOneOption
Require a single definition.
WARNING: Does not perform nested checks, as this does not run the merge function!
Located at lib/options.nix:262 in <nixpkgs>
.
lib.options.mergeUniqueOption
Require a single definition.
NOTE: When the type is not checked completely by check, pass a merge function for further checking (of sub-attributes, etc).
message
Function argument
merge
WARNING: the default merge function assumes that the definition is a valid (option) value. You MUST pass a merge function if the return value needs to be - type checked beyond what .check does (which should be very litte; only on the value head; not attribute values, etc) - if you want attribute values to be checked, or list items - if you want coercedTo-like behavior to work
loc
Function argument
defs
Function argument
Located at lib/options.nix:269 in <nixpkgs>
.
lib.options.mergeEqualOption
“Merge” option definitions by checking that they all have the same value.
loc
Function argument
defs
Function argument
Located at lib/options.nix:284 in <nixpkgs>
.
lib.options.getValues
Type: getValues :: [ { value :: a; } ] -> [a]
Extracts values of all “value” keys of the given list.
lib.options.getValues
usage examplegetValues [ { value = 1; } { value = 2; } ] // => [ 1 2 ]
getValues [ ] // => [ ]
Located at lib/options.nix:304 in <nixpkgs>
.
lib.options.getFiles
Type: getFiles :: [ { file :: a; } ] -> [a]
Extracts values of all “file” keys of the given list
lib.options.getFiles
usage examplegetFiles [ { file = "file1"; } { file = "file2"; } ] // => [ "file1" "file2" ]
getFiles [ ] // => [ ]
Located at lib/options.nix:314 in <nixpkgs>
.
lib.options.scrubOptionValue
This function recursively removes all derivation attributes from
x
except for the name
attribute.
This is to make the generation of options.xml
much more
efficient: the XML representation of derivations is very large
(on the order of megabytes) and is not actually used by the
manual generator.
This function was made obsolete by renderOptionValue and is kept for compatibility with out-of-tree code.
x
Function argument
Located at lib/options.nix:372 in <nixpkgs>
.
lib.options.renderOptionValue
Ensures that the given option value (default or example) is a _type
d string
by rendering Nix values to literalExpression
s.
v
Function argument
Located at lib/options.nix:383 in <nixpkgs>
.
lib.options.literalExpression
For use in the defaultText
and example
option attributes. Causes the
given string to be rendered verbatim in the documentation as Nix code. This
is necessary for complex values, e.g. functions, or values that depend on
other values or packages.
text
Function argument
Located at lib/options.nix:396 in <nixpkgs>
.
lib.options.mdDoc
Transition marker for documentation that’s already migrated to markdown syntax. Has been a no-op for some while and been removed from nixpkgs. Kept here to alert downstream users who may not be aware of the migration’s completion that it should be removed from modules.
Located at lib/options.nix:407 in <nixpkgs>
.
lib.options.literalMD
For use in the defaultText
and example
option attributes. Causes the
given MD text to be inserted verbatim in the documentation, for when
a literalExpression
would be too hard to read.
text
Function argument
Located at lib/options.nix:413 in <nixpkgs>
.
lib.options.showOption
Convert an option, described as a list of the option parts to a human-readable version.
parts
Function argument
lib.options.showOption
usage example(showOption ["foo" "bar" "baz"]) == "foo.bar.baz"
(showOption ["foo" "bar.baz" "tux"]) == "foo.\"bar.baz\".tux"
(showOption ["windowManager" "2bwm" "enable"]) == "windowManager.\"2bwm\".enable"
Placeholders will not be quoted as they are not actual values:
(showOption ["foo" "*" "bar"]) == "foo.*.bar"
(showOption ["foo" "<name>" "bar"]) == "foo.<name>.bar"
Located at lib/options.nix:431 in <nixpkgs>
.
Functions for working with path values.
lib.path.append
Type: append :: Path -> String -> Path
Append a subpath string to a path.
Like path + ("/" + string)
but safer, because it errors instead of returning potentially surprising results.
More specifically, it checks that the first argument is a path value type,
and that the second argument is a valid subpath string.
Laws:
Not influenced by subpath normalisation:
append p s == append p (subpath.normalise s)
path
The absolute path to append to
subpath
The subpath string to append
lib.path.append
usage exampleappend /foo "bar/baz"
=> /foo/bar/baz
# subpaths don't need to be normalised
append /foo "./bar//baz/./"
=> /foo/bar/baz
# can append to root directory
append /. "foo/bar"
=> /foo/bar
# first argument needs to be a path value type
append "/foo" "bar"
=> <error>
# second argument needs to be a valid subpath string
append /foo /bar
=> <error>
append /foo ""
=> <error>
append /foo "/bar"
=> <error>
append /foo "../bar"
=> <error>
Located at lib/path/default.nix:192 in <nixpkgs>
.
lib.path.hasPrefix
Type: hasPrefix :: Path -> Path -> Bool
Whether the first path is a component-wise prefix of the second path.
Laws:
hasPrefix p q
is only true if q == append p s
for some subpath s
.
hasPrefix
is a non-strict partial order over the set of all path values.
path1
Function argument
lib.path.hasPrefix
usage examplehasPrefix /foo /foo/bar
=> true
hasPrefix /foo /foo
=> true
hasPrefix /foo/bar /foo
=> false
hasPrefix /. /foo
=> true
Located at lib/path/default.nix:226 in <nixpkgs>
.
lib.path.removePrefix
Type: removePrefix :: Path -> Path -> String
Remove the first path as a component-wise prefix from the second path. The result is a normalised subpath string.
Laws:
Inverts append
for normalised subpath string:
removePrefix p (append p s) == subpath.normalise s
path1
Function argument
lib.path.removePrefix
usage exampleremovePrefix /foo /foo/bar/baz
=> "./bar/baz"
removePrefix /foo /foo
=> "./."
removePrefix /foo/bar /foo
=> <error>
removePrefix /. /foo
=> "./foo"
Located at lib/path/default.nix:271 in <nixpkgs>
.
lib.path.splitRoot
Type: splitRoot :: Path -> { root :: Path, subpath :: String }
Split the filesystem root from a path. The result is an attribute set with these attributes:
root
: The filesystem root of the path, meaning that this directory has no parent directory.
subpath
: The normalised subpath string that when appended to root
returns the original path.
Laws:
path
The path to split the root off of
lib.path.splitRoot
usage examplesplitRoot /foo/bar
=> { root = /.; subpath = "./foo/bar"; }
splitRoot /.
=> { root = /.; subpath = "./."; }
# Nix neutralises `..` path components for all path values automatically
splitRoot /foo/../bar
=> { root = /.; subpath = "./bar"; }
splitRoot "/foo/bar"
=> <error>
Located at lib/path/default.nix:336 in <nixpkgs>
.
lib.path.hasStorePathPrefix
Type: hasStorePathPrefix :: Path -> Bool
Whether a path has a store path as a prefix.
As with all functions of this lib.path
library, it does not work on paths in strings,
which is how you’d typically get store paths.
Instead, this function only handles path values themselves, which occur when Nix files in the store use relative path expressions.
path
Function argument
lib.path.hasStorePathPrefix
usage example# Subpaths of derivation outputs have a store path as a prefix
hasStorePathPrefix /nix/store/nvl9ic0pj1fpyln3zaqrf4cclbqdfn1j-foo/bar/baz
=> true
# The store directory itself is not a store path
hasStorePathPrefix /nix/store
=> false
# Derivation outputs are store paths themselves
hasStorePathPrefix /nix/store/nvl9ic0pj1fpyln3zaqrf4cclbqdfn1j-foo
=> true
# Paths outside the Nix store don't have a store path prefix
hasStorePathPrefix /home/user
=> false
# Not all paths under the Nix store are store paths
hasStorePathPrefix /nix/store/.links/10gg8k3rmbw8p7gszarbk7qyd9jwxhcfq9i6s5i0qikx8alkk4hq
=> false
# Store derivations are also store paths themselves
hasStorePathPrefix /nix/store/nvl9ic0pj1fpyln3zaqrf4cclbqdfn1j-foo.drv
=> true
Located at lib/path/default.nix:390 in <nixpkgs>
.
lib.path.subpath.isValid
Type: subpath.isValid :: String -> Bool
Whether a value is a valid subpath string.
A subpath string points to a specific file or directory within an absolute base directory.
It is a stricter form of a relative path that excludes ..
components, since those could escape the base directory.
The value is a string.
The string is not empty.
The string doesn’t start with a /
.
The string doesn’t contain any ..
path components.
value
The value to check
lib.path.subpath.isValid
usage example# Not a string
subpath.isValid null
=> false
# Empty string
subpath.isValid ""
=> false
# Absolute path
subpath.isValid "/foo"
=> false
# Contains a `..` path component
subpath.isValid "../foo"
=> false
# Valid subpath
subpath.isValid "foo/bar"
=> true
# Doesn't need to be normalised
subpath.isValid "./foo//bar/"
=> true
Located at lib/path/default.nix:447 in <nixpkgs>
.
lib.path.subpath.join
Type: subpath.join :: [ String ] -> String
Join subpath strings together using /
, returning a normalised subpath string.
Like concatStringsSep "/"
but safer, specifically:
All elements must be valid subpath strings.
The result gets normalised.
The edge case of an empty list gets properly handled by returning the neutral subpath "./."
.
Laws:
Associativity:
subpath.join [ x (subpath.join [ y z ]) ] == subpath.join [ (subpath.join [ x y ]) z ]
Identity - "./."
is the neutral element for normalised paths:
subpath.join [ ] == "./."
subpath.join [ (subpath.normalise p) "./." ] == subpath.normalise p
subpath.join [ "./." (subpath.normalise p) ] == subpath.normalise p
Normalisation - the result is normalised:
subpath.join ps == subpath.normalise (subpath.join ps)
For non-empty lists, the implementation is equivalent to normalising the result of concatStringsSep "/"
.
Note that the above laws can be derived from this one:
ps != [] -> subpath.join ps == subpath.normalise (concatStringsSep "/" ps)
subpaths
The list of subpaths to join together
lib.path.subpath.join
usage examplesubpath.join [ "foo" "bar/baz" ]
=> "./foo/bar/baz"
# normalise the result
subpath.join [ "./foo" "." "bar//./baz/" ]
=> "./foo/bar/baz"
# passing an empty list results in the current directory
subpath.join [ ]
=> "./."
# elements must be valid subpath strings
subpath.join [ /foo ]
=> <error>
subpath.join [ "" ]
=> <error>
subpath.join [ "/foo" ]
=> <error>
subpath.join [ "../foo" ]
=> <error>
Located at lib/path/default.nix:510 in <nixpkgs>
.
lib.path.subpath.components
Type: subpath.components :: String -> [ String ]
Split a subpath into its path component strings. Throw an error if the subpath isn’t valid. Note that the returned path components are also valid subpath strings, though they are intentionally not normalised.
Laws:
Splitting a subpath into components and joining the components gives the same subpath but normalised:
subpath.join (subpath.components s) == subpath.normalise s
subpath
The subpath string to split into components
lib.path.subpath.components
usage examplesubpath.components "."
=> [ ]
subpath.components "./foo//bar/./baz/"
=> [ "foo" "bar" "baz" ]
subpath.components "/foo"
=> <error>
Located at lib/path/default.nix:552 in <nixpkgs>
.
lib.path.subpath.normalise
Type: subpath.normalise :: String -> String
Normalise a subpath. Throw an error if the subpath isn’t valid.
Limit repeating /
to a single one.
Remove redundant .
components.
Remove trailing /
and /.
.
Add leading ./
.
Laws:
Idempotency - normalising multiple times gives the same result:
subpath.normalise (subpath.normalise p) == subpath.normalise p
Uniqueness - there’s only a single normalisation for the paths that lead to the same file system node:
subpath.normalise p != subpath.normalise q -> $(realpath ${p}) != $(realpath ${q})
Don’t change the result when appended to a Nix path value:
append base p == append base (subpath.normalise p)
Don’t change the path according to realpath
:
$(realpath ${p}) == $(realpath ${subpath.normalise p})
Only error on invalid subpaths:
builtins.tryEval (subpath.normalise p)).success == subpath.isValid p
subpath
The subpath string to normalise
lib.path.subpath.normalise
usage example# limit repeating `/` to a single one
subpath.normalise "foo//bar"
=> "./foo/bar"
# remove redundant `.` components
subpath.normalise "foo/./bar"
=> "./foo/bar"
# add leading `./`
subpath.normalise "foo/bar"
=> "./foo/bar"
# remove trailing `/`
subpath.normalise "foo/bar/"
=> "./foo/bar"
# remove trailing `/.`
subpath.normalise "foo/bar/."
=> "./foo/bar"
# Return the current directory as `./.`
subpath.normalise "."
=> "./."
# error on `..` path components
subpath.normalise "foo/../bar"
=> <error>
# error on empty string
subpath.normalise ""
=> <error>
# error on absolute path
subpath.normalise "/foo"
=> <error>
Located at lib/path/default.nix:633 in <nixpkgs>
.
Functions for querying information about the filesystem without copying any files to the Nix store.
lib.filesystem.pathType
The type of a path. The path needs to exist and be accessible. The result is either “directory” for a directory, “regular” for a regular file, “symlink” for a symlink, or “unknown” for anything else.
The path to query
pathType :: Path -> String
lib.filesystem.pathType
usage examplepathType /.
=> "directory"
pathType /some/file.nix
=> "regular"
Located at lib/filesystem.nix:62 in <nixpkgs>
.
lib.filesystem.pathIsDirectory
Whether a path exists and is a directory.
path
1. Function argument
pathIsDirectory :: Path -> Bool
lib.filesystem.pathIsDirectory
usage examplepathIsDirectory /.
=> true
pathIsDirectory /this/does/not/exist
=> false
pathIsDirectory /some/file.nix
=> false
Located at lib/filesystem.nix:111 in <nixpkgs>
.
lib.filesystem.pathIsRegularFile
Whether a path exists and is a regular file, meaning not a symlink or any other special file type.
path
1. Function argument
pathIsRegularFile :: Path -> Bool
lib.filesystem.pathIsRegularFile
usage examplepathIsRegularFile /.
=> false
pathIsRegularFile /this/does/not/exist
=> false
pathIsRegularFile /some/file.nix
=> true
Located at lib/filesystem.nix:147 in <nixpkgs>
.
lib.filesystem.haskellPathsInDir
A map of all haskell packages defined in the given path, identified by having a cabal file with the same name as the directory itself.
root
The directory within to search
lib.filesystem.locateDominatingFile
Find the first directory containing a file matching ‘pattern’ upward from a given ‘file’. Returns ‘null’ if no directories contain a file matching ‘pattern’.
pattern
The pattern to search for
file
The file to start searching upward from
RegExp -> Path -> Nullable { path : Path; matches : [ MatchResults ]; }
Located at lib/filesystem.nix:205 in <nixpkgs>
.
lib.filesystem.listFilesRecursive
Given a directory, return a flattened list of all files within it recursively.
dir
The path to recursively list
lib.filesystem.packagesFromDirectoryRecursive
Transform a directory tree containing package files suitable for
callPackage
into a matching nested attribute set of derivations.
For a directory tree like this:
my-packages
├── a.nix
├── b.nix
├── c
│ ├── my-extra-feature.patch
│ ├── package.nix
│ └── support-definitions.nix
└── my-namespace
├── d.nix
├── e.nix
└── f
└── package.nix
packagesFromDirectoryRecursive
will produce an attribute set like this:
# packagesFromDirectoryRecursive {
# callPackage = pkgs.callPackage;
# directory = ./my-packages;
# }
{
a = pkgs.callPackage ./my-packages/a.nix { };
b = pkgs.callPackage ./my-packages/b.nix { };
c = pkgs.callPackage ./my-packages/c/package.nix { };
my-namespace = {
d = pkgs.callPackage ./my-packages/my-namespace/d.nix { };
e = pkgs.callPackage ./my-packages/my-namespace/e.nix { };
f = pkgs.callPackage ./my-packages/my-namespace/f/package.nix { };
};
}
In particular:
If the input directory contains a package.nix
file, then
callPackage <directory>/package.nix { }
is returned.
Otherwise, the input directory’s contents are listed and transformed into an attribute set.
If a file name has the .nix
extension, it is turned into attribute
where:
The attribute name is the file name without the .nix
extension
The attribute value is callPackage <file path> { }
Other files are ignored.
Directories are turned into an attribute where:
The attribute name is the name of the directory
The attribute value is the result of calling
packagesFromDirectoryRecursive { ... }
on the directory.
As a result, directories with no .nix
files (including empty
directories) will be transformed into empty attribute sets.
Attribute set containing the following attributes. Additional attributes are ignored.
callPackage
pkgs.callPackage
Type: Path -> AttrSet -> a
directory
The directory to read package files from
Type: Path
packagesFromDirectoryRecursive :: AttrSet -> AttrSet
lib.filesystem.packagesFromDirectoryRecursive
usage examplepackagesFromDirectoryRecursive {
inherit (pkgs) callPackage;
directory = ./my-packages;
}
=> { ... }
lib.makeScope pkgs.newScope (
self: packagesFromDirectoryRecursive {
callPackage = self.callPackage;
directory = ./my-packages;
}
)
=> { ... }
Located at lib/filesystem.nix:357 in <nixpkgs>
.
The lib.fileset
library allows you to work with file sets.
A file set is a (mathematical) set of local files that can be added to the Nix store for use in Nix derivations.
File sets are easy and safe to use, providing obvious and composable semantics with good error messages to prevent mistakes.
Basics:
Create a file set from a path that may be missing.
lib.fileset.trace
/lib.fileset.traceVal
:
Pretty-print file sets for debugging.
Add files in file sets to the store to use as derivation sources.
The list of files contained in a file set.
Combinators:
lib.fileset.union
/lib.fileset.unions
:
Create a larger file set from all the files in multiple file sets.
Create a smaller file set from only the files in both file sets.
Create a smaller file set containing all files that are in one file set, but not another one.
Filtering:
Create a file set from all files that satisisfy a predicate in a directory.
Utilities:
Create a file set from a lib.sources
-based value.
lib.fileset.gitTracked
/lib.fileset.gitTrackedWith
:
Create a file set from all tracked files in a local Git repository.
If you need more file set functions, see this issue to request it.
All functions accepting file sets as arguments can also accept paths as arguments. Such path arguments are implicitly coerced to file sets containing all files under that path:
A path to a file turns into a file set containing that single file.
A path to a directory turns into a file set containing all files recursively in that directory.
If the path points to a non-existent location, an error is thrown.
Just like in Git, file sets cannot represent empty directories. Because of this, a path to a directory that contains no files (recursively) will turn into a file set containing no files.
File set coercion does not add any of the files under the coerced paths to the store.
Only the toSource
function adds files to the Nix store, and only those files contained in the fileset
argument.
This is in contrast to using paths in string interpolation, which does add the entire referenced path to the store.
Assume we are in a local directory with a file hierarchy like this:
├─ a/
│ ├─ x (file)
│ └─ b/
│ └─ y (file)
└─ c/
└─ d/
Here’s a listing of which files get included when different path expressions get coerced to file sets:
./.
as a file set contains both a/x
and a/b/y
(c/
does not contain any files and is therefore omitted).
./a
as a file set contains both a/x
and a/b/y
.
./a/x
as a file set contains only a/x
.
./a/b
as a file set contains only a/b/y
.
./c
as a file set is empty, since neither c
nor c/d
contain any files.
lib.fileset.maybeMissing
Create a file set from a path that may or may not exist:
If the path does exist, the path is coerced to a file set.
If the path does not exist, a file set containing no files is returned.
path
1. Function argument
maybeMissing :: Path -> FileSet
lib.fileset.maybeMissing
usage example# All files in the current directory, but excluding main.o if it exists
difference ./. (maybeMissing ./main.o)
Located at lib/fileset/default.nix:189 in <nixpkgs>
.
lib.fileset.trace
Incrementally evaluate and trace a file set in a pretty way. This function is only intended for debugging purposes. The exact tracing format is unspecified and may change.
This function takes a final argument to return.
In comparison, traceVal
returns
the given file set argument.
This variant is useful for tracing file sets in the Nix repl.
fileset
The file set to trace.
This argument can also be a path, which gets implicitly coerced to a file set.
val
The value to return.
trace :: FileSet -> Any -> Any
lib.fileset.trace
usage exampletrace (unions [ ./Makefile ./src ./tests/run.sh ]) null
=>
trace: /home/user/src/myProject
trace: - Makefile (regular)
trace: - src (all files in directory)
trace: - tests
trace: - run.sh (regular)
null
Located at lib/fileset/default.nix:251 in <nixpkgs>
.
lib.fileset.traceVal
Incrementally evaluate and trace a file set in a pretty way. This function is only intended for debugging purposes. The exact tracing format is unspecified and may change.
This function returns the given file set.
In comparison, trace
takes another argument to return.
This variant is useful for tracing file sets passed as arguments to other functions.
fileset
The file set to trace and return.
This argument can also be a path, which gets implicitly coerced to a file set.
traceVal :: FileSet -> FileSet
lib.fileset.traceVal
usage exampletoSource {
root = ./.;
fileset = traceVal (unions [
./Makefile
./src
./tests/run.sh
]);
}
=>
trace: /home/user/src/myProject
trace: - Makefile (regular)
trace: - src (all files in directory)
trace: - tests
trace: - run.sh (regular)
"/nix/store/...-source"
Located at lib/fileset/default.nix:311 in <nixpkgs>
.
lib.fileset.toSource
Add the local files contained in fileset
to the store as a single store path rooted at root
.
The result is the store path as a string-like value, making it usable e.g. as the src
of a derivation, or in string interpolation:
stdenv.mkDerivation {
src = lib.fileset.toSource { ... };
# ...
}
The name of the store path is always source
.
Takes an attribute set with the following attributes
root
(Path; required)The local directory path that will correspond to the root of the resulting store path.
Paths in strings, including Nix store paths, cannot be passed as root
.
root
has to be a directory.
Changing root
only affects the directory structure of the resulting store path, it does not change which files are added to the store.
The only way to change which files get added to the store is by changing the fileset
attribute.
fileset
(FileSet; required)The file set whose files to import into the store. File sets can be created using other functions in this library. This argument can also be a path, which gets implicitly coerced to a file set.
If a directory does not recursively contain any file, it is omitted from the store path contents.
toSource :: {
root :: Path,
fileset :: FileSet,
} -> SourceLike
lib.fileset.toSource
usage example# Import the current directory into the store
# but only include files under ./src
toSource {
root = ./.;
fileset = ./src;
}
=> "/nix/store/...-source"
# Import the current directory into the store
# but only include ./Makefile and all files under ./src
toSource {
root = ./.;
fileset = union
./Makefile
./src;
}
=> "/nix/store/...-source"
# Trying to include a file outside the root will fail
toSource {
root = ./.;
fileset = unions [
./Makefile
./src
../LICENSE
];
}
=> <error>
# The root needs to point to a directory that contains all the files
toSource {
root = ../.;
fileset = unions [
./Makefile
./src
../LICENSE
];
}
=> "/nix/store/...-source"
# The root has to be a local filesystem path
toSource {
root = "/nix/store/...-source";
fileset = ./.;
}
=> <error>
Located at lib/fileset/default.nix:426 in <nixpkgs>
.
lib.fileset.toList
The list of file paths contained in the given file set.
This function is strict in the entire file set.
This is in contrast with combinators lib.fileset.union
,
lib.fileset.intersection
and lib.fileset.difference
.
Thus it is recommended to call toList
on file sets created using the combinators,
instead of doing list processing on the result of toList
.
The resulting list of files can be turned back into a file set using lib.fileset.unions
.
fileset
The file set whose file paths to return. This argument can also be a path, which gets implicitly coerced to a file set.
toList :: FileSet -> [ Path ]
lib.fileset.toList
usage exampletoList ./.
[ ./README.md ./Makefile ./src/main.c ./src/main.h ]
toList (difference ./. ./src)
[ ./README.md ./Makefile ]
Located at lib/fileset/default.nix:524 in <nixpkgs>
.
lib.fileset.union
The file set containing all files that are in either of two given file sets.
This is the same as unions
,
but takes just two file sets instead of a list.
See also Union (set theory).
The given file sets are evaluated as lazily as possible, with the first argument being evaluated first if needed.
fileset1
The first file set. This argument can also be a path, which gets implicitly coerced to a file set.
fileset2
The second file set. This argument can also be a path, which gets implicitly coerced to a file set.
union :: FileSet -> FileSet -> FileSet
lib.fileset.union
usage example# Create a file set containing the file `Makefile`
# and all files recursively in the `src` directory
union ./Makefile ./src
# Create a file set containing the file `Makefile`
# and the LICENSE file from the parent directory
union ./Makefile ../LICENSE
Located at lib/fileset/default.nix:569 in <nixpkgs>
.
lib.fileset.unions
The file set containing all files that are in any of the given file sets.
This is the same as union
,
but takes a list of file sets instead of just two.
See also Union (set theory).
The given file sets are evaluated as lazily as possible, with earlier elements being evaluated first if needed.
filesets
A list of file sets. The elements can also be paths, which get implicitly coerced to file sets.
unions :: [ FileSet ] -> FileSet
lib.fileset.unions
usage example# Create a file set containing selected files
unions [
# Include the single file `Makefile` in the current directory
# This errors if the file doesn't exist
./Makefile
# Recursively include all files in the `src/code` directory
# If this directory is empty this has no effect
./src/code
# Include the files `run.sh` and `unit.c` from the `tests` directory
./tests/run.sh
./tests/unit.c
# Include the `LICENSE` file from the parent directory
../LICENSE
]
Located at lib/fileset/default.nix:632 in <nixpkgs>
.
lib.fileset.intersection
The file set containing all files that are in both of two given file sets. See also Intersection (set theory).
The given file sets are evaluated as lazily as possible, with the first argument being evaluated first if needed.
fileset1
The first file set. This argument can also be a path, which gets implicitly coerced to a file set.
fileset2
The second file set. This argument can also be a path, which gets implicitly coerced to a file set.
intersection :: FileSet -> FileSet -> FileSet
lib.fileset.intersection
usage example# Limit the selected files to the ones in ./., so only ./src and ./Makefile
intersection ./. (unions [ ../LICENSE ./src ./Makefile ])
Located at lib/fileset/default.nix:683 in <nixpkgs>
.
lib.fileset.difference
The file set containing all files from the first file set that are not in the second file set. See also Difference (set theory).
The given file sets are evaluated as lazily as possible, with the first argument being evaluated first if needed.
positive
The positive file set. The result can only contain files that are also in this file set. This argument can also be a path, which gets implicitly coerced to a file set.
negative
The negative file set. The result will never contain files that are also in this file set. This argument can also be a path, which gets implicitly coerced to a file set.
union :: FileSet -> FileSet -> FileSet
lib.fileset.difference
usage example# Create a file set containing all files from the current directory,
# except ones under ./tests
difference ./. ./tests
let
# A set of Nix-related files
nixFiles = unions [ ./default.nix ./nix ./tests/default.nix ];
in
# Create a file set containing all files under ./tests, except ones in `nixFiles`,
# meaning only without ./tests/default.nix
difference ./tests nixFiles
Located at lib/fileset/default.nix:746 in <nixpkgs>
.
lib.fileset.fileFilter
Filter a file set to only contain files matching some predicate.
predicate
The predicate function to call on all files contained in given file set. A file is included in the resulting file set if this function returns true for it.
This function is called with an attribute set containing these attributes:
name
(String): The name of the file
type
(String, one of "regular"
, "symlink"
or "unknown"
): The type of the file.
This matches result of calling builtins.readFileType
on the file’s path.
hasExt
(String -> Bool): Whether the file has a certain file extension.
hasExt ext
is true only if hasSuffix ".${ext}" name
.
This also means that e.g. for a file with name .gitignore
,
hasExt "gitignore"
is true.
Other attributes may be added in the future.
path
The path whose files to filter
fileFilter ::
({
name :: String,
type :: String,
hasExt :: String -> Bool,
...
} -> Bool)
-> Path
-> FileSet
lib.fileset.fileFilter
usage example# Include all regular `default.nix` files in the current directory
fileFilter (file: file.name == "default.nix") ./.
# Include all non-Nix files from the current directory
fileFilter (file: ! file.hasExt "nix") ./.
# Include all files that start with a "." in the current directory
fileFilter (file: hasPrefix "." file.name) ./.
# Include all regular files (not symlinks or others) in the current directory
fileFilter (file: file.type == "regular") ./.
Located at lib/fileset/default.nix:829 in <nixpkgs>
.
lib.fileset.fromSource
Create a file set with the same files as a lib.sources
-based value.
This does not import any of the files into the store.
This can be used to gradually migrate from lib.sources
-based filtering to lib.fileset
.
A file set can be turned back into a source using toSource
.
File sets cannot represent empty directories.
Turning the result of this function back into a source using toSource
will therefore not preserve empty directories.
source
1. Function argument
fromSource :: SourceLike -> FileSet
lib.fileset.fromSource
usage example# There's no cleanSource-like function for file sets yet,
# but we can just convert cleanSource to a file set and use it that way
toSource {
root = ./.;
fileset = fromSource (lib.sources.cleanSource ./.);
}
# Keeping a previous sourceByRegex (which could be migrated to `lib.fileset.unions`),
# but removing a subdirectory using file set functions
difference
(fromSource (lib.sources.sourceByRegex ./. [
"^README\.md$"
# This regex includes everything in ./doc
"^doc(/.*)?$"
])
./doc/generated
# Use cleanSource, but limit it to only include ./Makefile and files under ./src
intersection
(fromSource (lib.sources.cleanSource ./.))
(unions [
./Makefile
./src
]);
Located at lib/fileset/default.nix:908 in <nixpkgs>
.
lib.fileset.gitTracked
Create a file set containing all Git-tracked files in a repository.
This function behaves like gitTrackedWith { }
- using the defaults.
path
The path to the working directory of a local Git repository.
This directory must contain a .git
file or subdirectory.
gitTracked :: Path -> FileSet
lib.fileset.gitTracked
usage example# Include all files tracked by the Git repository in the current directory
gitTracked ./.
# Include only files tracked by the Git repository in the parent directory
# that are also in the current directory
intersection ./. (gitTracked ../.)
Located at lib/fileset/default.nix:969 in <nixpkgs>
.
lib.fileset.gitTrackedWith
Create a file set containing all Git-tracked files in a repository. The first argument allows configuration with an attribute set, while the second argument is the path to the Git working tree.
gitTrackedWith
does not perform any filtering when the path is a Nix store path and not a repository.
In this way, it accommodates the use case where the expression that makes the gitTracked
call does not reside in an actual git repository anymore,
and has presumably already been fetched in a way that excludes untracked files.
Fetchers with such equivalent behavior include builtins.fetchGit
, builtins.fetchTree
(experimental), and pkgs.fetchgit
when used without leaveDotGit
.
If you don’t need the configuration,
you can use gitTracked
instead.
This is equivalent to the result of unions
on all files returned by git ls-files
(which uses --cached
by default).
Currently this function is based on builtins.fetchGit
As such, this function causes all Git-tracked files to be unnecessarily added to the Nix store,
without being re-usable by toSource
.
This may change in the future.
options
(attribute set)recurseSubmodules
(optional, default: false
)Whether to recurse into Git submodules to also include their tracked files.
If true
, this is equivalent to passing the –recurse-submodules flag to git ls-files
.
path
The path to the working directory of a local Git repository.
This directory must contain a .git
file or subdirectory.
gitTrackedWith :: { recurseSubmodules :: Bool ? false } -> Path -> FileSet
lib.fileset.gitTrackedWith
usage example# Include all files tracked by the Git repository in the current directory
# and any submodules under it
gitTracked { recurseSubmodules = true; } ./.
Located at lib/fileset/default.nix:1031 in <nixpkgs>
.
Functions for copying sources to the Nix store.
lib.sources.commitIdFromGitRepo
Get the commit id of a git repo.
path
Function argument
lib.sources.commitIdFromGitRepo
usage examplecommitIdFromGitRepo <nixpkgs/.git>
Located at lib/sources.nix:273 in <nixpkgs>
.
lib.sources.cleanSource
Filters a source tree removing version control files and directories using cleanSourceFilter.
src
Function argument
lib.sources.cleanSource
usage examplecleanSource ./.
Located at lib/sources.nix:275 in <nixpkgs>
.
lib.sources.cleanSourceWith
Like builtins.filterSource
, except it will compose with itself,
allowing you to chain multiple calls together without any
intermediate copies being put in the nix store.
src
A path or cleanSourceWith result to filter and/or rename.
filter
Optional with default value: constant true (include everything) The function will be combined with the && operator such that src.filter is called lazily. For implementing a filter, see https://nixos.org/nix/manual/#builtin-filterSource Type: A function (path -> type -> bool)
name
Optional name to use as part of the store path. This defaults to src.name
or otherwise "source"
.
lib.sources.cleanSourceWith
usage examplelib.cleanSourceWith {
filter = f;
src = lib.cleanSourceWith {
filter = g;
src = ./.;
};
}
# Succeeds!
builtins.filterSource f (builtins.filterSource g ./.)
# Fails!
Located at lib/sources.nix:276 in <nixpkgs>
.
lib.sources.cleanSourceFilter
A basic filter for cleanSourceWith
that removes
directories of version control system, backup files (*~)
and some generated files.
name
Function argument
type
Function argument
Located at lib/sources.nix:277 in <nixpkgs>
.
lib.sources.sourceByRegex
Filter sources by a list of regular expressions.
src
Function argument
regexes
Function argument
lib.sources.sourceByRegex
usage examplesrc = sourceByRegex ./my-subproject [".*\.py$" "^database.sql$"]
Located at lib/sources.nix:281 in <nixpkgs>
.
lib.sources.sourceFilesBySuffices
Type: sourceLike -> [String] -> Source
Get all files ending with the specified suffices from the given
source directory or its descendants, omitting files that do not match
any suffix. The result of the example below will include files like
./dir/module.c
and ./dir/subdir/doc.xml
if present.
src
Path or source containing the files to be returned
exts
A list of file suffix strings
lib.sources.sourceFilesBySuffices
usage examplesourceFilesBySuffices ./. [ ".xml" ".c" ]
Located at lib/sources.nix:282 in <nixpkgs>
.
lib.sources.trace
Type: sources.trace :: sourceLike -> Source
Add logging to a source, for troubleshooting the filtering behavior.
src
Source to debug. The returned source will behave like this source, but also log its filter invocations.
Located at lib/sources.nix:284 in <nixpkgs>
.
lib.cli.toGNUCommandLineShell
Automatically convert an attribute set to command-line options.
This helps protect against malformed command lines and also to reduce boilerplate related to command-line construction for simple use cases.
toGNUCommandLineShell
returns an escaped shell string.
options
How to format the arguments, see toGNUCommandLine
attrs
The attributes to transform into arguments.
lib.cli.toGNUCommandLineShell
usage examplecli.toGNUCommandLineShell {} {
data = builtins.toJSON { id = 0; };
X = "PUT";
retry = 3;
retry-delay = null;
url = [ "https://example.com/foo" "https://example.com/bar" ];
silent = false;
verbose = true;
}
=> "'-X' 'PUT' '--data' '{\"id\":0}' '--retry' '3' '--url' 'https://example.com/foo' '--url' 'https://example.com/bar' '--verbose'";
Located at lib/cli.nix:43 in <nixpkgs>
.
lib.cli.toGNUCommandLine
Automatically convert an attribute set to a list of command-line options.
toGNUCommandLine
returns a list of string arguments.
options
How to format the arguments, see below.
attrs
The attributes to transform into arguments.
mkOptionName
How to string-format the option name;
By default one character is a short option (-
), more than one characters a long option (--
).
mkBool
How to format a boolean value to a command list; By default it’s a flag option (only the option name if true, left out completely if false).
mkList
How to format a list value to a command list;
By default the option name is repeated for each value and mkOption
is applied to the values themselves.
mkOption
How to format any remaining value to a command list;
On the toplevel, booleans and lists are handled by mkBool
and mkList
, though they can still appear as values of a list.
By default, everything is printed verbatim and complex types are forbidden (lists, attrsets, functions). null
values are omitted.
optionValueSeparator
How to separate an option from its flag;
By default, there is no separator, so option -c
and value 5
would become [“-c” “5”].
This is useful if the command requires equals, for example, -c=5
.
lib.cli.toGNUCommandLine
usage examplecli.toGNUCommandLine {} {
data = builtins.toJSON { id = 0; };
X = "PUT";
retry = 3;
retry-delay = null;
url = [ "https://example.com/foo" "https://example.com/bar" ];
silent = false;
verbose = true;
}
=> [
"-X" "PUT"
"--data" "{\"id\":0}"
"--retry" "3"
"--url" "https://example.com/foo"
"--url" "https://example.com/bar"
"--verbose"
]
Located at lib/cli.nix:119 in <nixpkgs>
.
Functions that generate widespread file formats from nix data structures.
They all follow a similar interface:
generator { config-attrs } data
config-attrs
are “holes” in the generators
with sensible default implementations that
can be overwritten. The default implementations
are mostly generators themselves, called with
their respective default values; they can be reused.
Tests can be found in ./tests/misc.nix
Further Documentation can be found here.
lib.generators.mkValueStringDefault
Convert a value to a sensible default string representation.
The builtin toString
function has some strange defaults,
suitable for bash scripts but not much else.
Empty set, there may be configuration options in the future
v
2. Function argument
Located at lib/generators.nix:90 in <nixpkgs>
.
lib.generators.mkKeyValueDefault
Generate a line of key k and value v, separated by character sep. If sep appears in k, it is escaped. Helper for synaxes with different separators.
mkValueString specifies how values should be formatted.
mkKeyValueDefault {} ":" "f:oo" "bar"
> "f\:oo:bar"
mkValueStringDefault {}
)Function to convert values to strings
sep
2. Function argument
k
3. Function argument
v
4. Function argument
Located at lib/generators.nix:147 in <nixpkgs>
.
lib.generators.toKeyValue
Generate a key-value-style config file from an attrset.
mkKeyValueDefault {} "="
)format a setting line from key and value
false
)allow lists as values for duplicate keys
""
)Initial indentation level
Located at lib/generators.nix:173 in <nixpkgs>
.
lib.generators.toINI
Generate an INI-style config file from an attrset of sections to an attrset of key-value pairs.
(name: escape [ "[" "]" ] name)
)apply transformations (e.g. escapes) to section names
{} "="
)format a setting line from key and value
false
)allow lists as values for duplicate keys
lib.generators.toINI
usage examplegenerators.toINI {} {
foo = { hi = "${pkgs.hello}"; ciao = "bar"; };
baz = { "also, integers" = 42; };
}
> [baz]
> also, integers=42
>
> [foo]
> ciao=bar
> hi=/nix/store/y93qql1p5ggfnaqjjqhxcw0vqw95rlz0-hello-2.10
The mk* configuration attributes can generically change the way sections and key-value strings are generated.
For more examples see the test cases in ./tests/misc.nix.
Located at lib/generators.nix:227 in <nixpkgs>
.
lib.generators.toINIWithGlobalSection
Generate an INI-style config file from an attrset specifying the global section (no header), and an attrset of sections to an attrset of key-value pairs.
(name: escape [ "[" "]" ] name)
)apply transformations (e.g. escapes) to section names
{} "="
)format a setting line from key and value
false
)allow lists as values for duplicate keys
global section key-value pairs
{}
)attrset of sections to key-value pairs
lib.generators.toINIWithGlobalSection
usage examplegenerators.toINIWithGlobalSection {} {
globalSection = {
someGlobalKey = "hi";
};
sections = {
foo = { hi = "${pkgs.hello}"; ciao = "bar"; };
baz = { "also, integers" = 42; };
}
> someGlobalKey=hi
>
> [baz]
> also, integers=42
>
> [foo]
> ciao=bar
> hi=/nix/store/y93qql1p5ggfnaqjjqhxcw0vqw95rlz0-hello-2.10
The mk* configuration attributes can generically change the way sections and key-value strings are generated.
For more examples see the test cases in ./tests/misc.nix.
If you don’t need a global section, you can also use
generators.toINI
directly, which only takes
the part in sections
.
Located at lib/generators.nix:305 in <nixpkgs>
.
lib.generators.toGitINI
Generate a git-config file from an attrset.
It has two major differences from the regular INI format:
values are indented with tabs
sections can have sub-sections
Further: https://git-scm.com/docs/git-config#EXAMPLES
lib.generators.toGitINI
usage examplegenerators.toGitINI {
url."ssh://git@github.com/".insteadOf = "https://github.com";
user.name = "edolstra";
}
> [url "ssh://git@github.com/"]
> insteadOf = "https://github.com"
>
> [user]
> name = "edolstra"
attrs
Key-value pairs to be converted to a git-config file. See: https://git-scm.com/docs/git-config#_variables for possible values.
Located at lib/generators.nix:353 in <nixpkgs>
.
lib.generators.mkDconfKeyValue
mkKeyValueDefault wrapper that handles dconf INI quirks. The main differences of the format is that it requires strings to be quoted.
Located at lib/generators.nix:400 in <nixpkgs>
.
lib.generators.toDconfINI
Generates INI in dconf keyfile style. See https://help.gnome.org/admin/system-admin-guide/stable/dconf-keyfiles.html.en for details.
Located at lib/generators.nix:406 in <nixpkgs>
.
lib.generators.withRecursion
Recurses through a Value
limited to a certain depth. (depthLimit
)
If the depth is exceeded, an error is thrown, unless throwOnDepthLimit
is set to false
.
If this option is not null, the given value will stop evaluating at a certain depth
true
)If this option is true, an error will be thrown, if a certain given depth is exceeded
The value to be evaluated recursively
Located at lib/generators.nix:426 in <nixpkgs>
.
lib.generators.toPretty
Pretty print a value, akin to builtins.trace
.
Should probably be a builtin as well.
The pretty-printed string should be suitable for rendering default values in the NixOS manual. In particular, it should be as close to a valid Nix expression as possible.
If this option is true, attrsets like { __pretty = fn; val = …; } will use fn to convert val to a pretty printed representation. (This means fn is type Val -> String.)
If this option is true, the output is indented with newlines for attribute sets and lists
Initial indentation level
The value to be pretty printed
Located at lib/generators.nix:483 in <nixpkgs>
.
lib.generators.toPlist
Translate a simple Nix expression to Plist notation.
Empty set, there may be configuration options in the future
The value to be converted to Plist
Located at lib/generators.nix:557 in <nixpkgs>
.
lib.generators.toDhall
Translate a simple Nix expression to Dhall notation.
Note that integers are translated to Integer and never the Natural type.
Empty set, there may be configuration options in the future
The value to be converted to Dhall
Located at lib/generators.nix:622 in <nixpkgs>
.
lib.generators.toLua
Translate a simple Nix expression to Lua representation with occasional Lua-inlines that can be constructed by mkLuaInline function.
Configuration:
multiline - by default is true which results in indented block-like view.
indent - initial indent.
asBindings - by default generate single value, but with this use attrset to set global vars.
Attention:
Regardless of multiline parameter there is no trailing newline.
true
)If this option is true, the output is indented with newlines for attribute sets and lists
""
)Initial indentation level
false
)Interpret as variable bindings
The value to be converted to Lua
toLua :: AttrSet -> Any -> String
lib.generators.toLua
usage examplegenerators.toLua {}
{
cmd = [ "typescript-language-server" "--stdio" ];
settings.workspace.library = mkLuaInline ''vim.api.nvim_get_runtime_file("", true)'';
}
->
{
["cmd"] = {
"typescript-language-server",
"--stdio"
},
["settings"] = {
["workspace"] = {
["library"] = (vim.api.nvim_get_runtime_file("", true))
}
}
}
Located at lib/generators.nix:704 in <nixpkgs>
.
lib.generators.mkLuaInline
Mark string as Lua expression to be inlined when processed by toLua.
expr
1. Function argument
A partial and basic implementation of GVariant formatted strings. See GVariant Format Strings for details.
This API is not considered fully stable and it might therefore change in backwards incompatible ways without prior notice.
lib.gvariant.isGVariant
Check if a value is a GVariant value
v
value to check
lib.gvariant.mkValue
Returns the GVariant value that most closely matches the given Nix value. If no GVariant value can be found unambiguously then error is thrown.
v
1. Function argument
lib.gvariant.mkArray
Returns the GVariant array from the given type of the elements and a Nix list.
elems
1. Function argument
mkArray :: [Any] -> gvariant
lib.gvariant.mkArray
usage example# Creating a string array
lib.gvariant.mkArray [ "a" "b" "c" ]
Located at lib/gvariant.nix:184 in <nixpkgs>
.
lib.gvariant.mkEmptyArray
Returns the GVariant array from the given empty Nix list.
elemType
1. Function argument
mkEmptyArray :: gvariant.type -> gvariant
lib.gvariant.mkEmptyArray
usage example# Creating an empty string array
lib.gvariant.mkEmptyArray (lib.gvariant.type.string)
Located at lib/gvariant.nix:223 in <nixpkgs>
.
lib.gvariant.mkVariant
Returns the GVariant variant from the given Nix value. Variants are containers of different GVariant type.
elem
1. Function argument
mkVariant :: Any -> gvariant
lib.gvariant.mkVariant
usage examplelib.gvariant.mkArray [
(lib.gvariant.mkVariant "a string")
(lib.gvariant.mkVariant (lib.gvariant.mkInt32 1))
]
Located at lib/gvariant.nix:258 in <nixpkgs>
.
lib.gvariant.mkDictionaryEntry
Returns the GVariant dictionary entry from the given key and value.
name
The key of the entry
value
The value of the entry
mkDictionaryEntry :: String -> Any -> gvariant
lib.gvariant.mkDictionaryEntry
usage example# A dictionary describing an Epiphany’s search provider
[
(lib.gvariant.mkDictionaryEntry "url" (lib.gvariant.mkVariant "https://duckduckgo.com/?q=%s&t=epiphany"))
(lib.gvariant.mkDictionaryEntry "bang" (lib.gvariant.mkVariant "!d"))
(lib.gvariant.mkDictionaryEntry "name" (lib.gvariant.mkVariant "DuckDuckGo"))
]
Located at lib/gvariant.nix:299 in <nixpkgs>
.
lib.gvariant.mkMaybe
Returns the GVariant maybe from the given element type.
elemType
1. Function argument
elem
2. Function argument
lib.gvariant.mkNothing
Returns the GVariant nothing from the given element type.
elemType
1. Function argument
lib.gvariant.mkJust
Returns the GVariant just from the given Nix value.
elem
1. Function argument
lib.gvariant.mkTuple
Returns the GVariant tuple from the given Nix list.
elems
1. Function argument
lib.gvariant.mkBoolean
Returns the GVariant boolean from the given Nix bool value.
v
1. Function argument
lib.gvariant.mkString
Returns the GVariant string from the given Nix string value.
v
1. Function argument
lib.gvariant.mkObjectpath
Returns the GVariant object path from the given Nix string value.
v
1. Function argument
lib.gvariant.mkUchar
Returns the GVariant uchar from the given Nix int value.
lib.gvariant.mkInt16
Returns the GVariant int16 from the given Nix int value.
lib.gvariant.mkUint16
Returns the GVariant uint16 from the given Nix int value.
lib.gvariant.mkInt32
Returns the GVariant int32 from the given Nix int value.
v
1. Function argument
lib.gvariant.mkUint32
Returns the GVariant uint32 from the given Nix int value.
lib.gvariant.mkInt64
Returns the GVariant int64 from the given Nix int value.
lib.gvariant.mkUint64
Returns the GVariant uint64 from the given Nix int value.
lib.gvariant.mkDouble
Returns the GVariant double from the given Nix float value.
v
1. Function argument
lib.customisation.overrideDerivation
overrideDerivation drv f
takes a derivation (i.e., the result
of a call to the builtin function derivation
) and returns a new
derivation in which the attributes of the original are overridden
according to the function f
. The function f
is called with
the original derivation attributes.
overrideDerivation
allows certain “ad-hoc” customisation
scenarios (e.g. in ~/.config/nixpkgs/config.nix). For instance,
if you want to “patch” the derivation returned by a package
function in Nixpkgs to build another version than what the
function itself provides.
For another application, see build-support/vm, where this function is used to build arbitrary derivations inside a QEMU virtual machine.
Note that in order to preserve evaluation errors, the new derivation’s outPath depends on the old one’s, which means that this function cannot be used in circular situations when the old derivation also depends on the new one.
You should in general prefer drv.overrideAttrs
over this function;
see the nixpkgs manual for more information on overriding.
drv
1. Function argument
f
2. Function argument
overrideDerivation :: Derivation -> ( Derivation -> AttrSet ) -> Derivation
lib.customisation.overrideDerivation
usage examplemySed = overrideDerivation pkgs.gnused (oldAttrs: {
name = "sed-4.2.2-pre";
src = fetchurl {
url = ftp://alpha.gnu.org/gnu/sed/sed-4.2.2-pre.tar.bz2;
hash = "sha256-MxBJRcM2rYzQYwJ5XKxhXTQByvSg5jZc5cSHEZoB2IY=";
};
patches = [];
});
Located at lib/customisation.nix:77 in <nixpkgs>
.
lib.customisation.makeOverridable
makeOverridable
takes a function from attribute set to attribute set and
injects override
attribute which can be used to override arguments of
the function.
Please refer to documentation on <pkg>.overrideDerivation
to learn about overrideDerivation
and caveats
related to its use.
f
1. Function argument
makeOverridable :: (AttrSet -> a) -> AttrSet -> a
lib.customisation.makeOverridable
usage examplenix-repl> x = {a, b}: { result = a + b; }
nix-repl> y = lib.makeOverridable x { a = 1; b = 2; }
nix-repl> y
{ override = «lambda»; overrideDerivation = «lambda»; result = 3; }
nix-repl> y.override { a = 10; }
{ override = «lambda»; overrideDerivation = «lambda»; result = 12; }
Located at lib/customisation.nix:131 in <nixpkgs>
.
lib.customisation.callPackageWith
Call the package function in the file fn
with the required
arguments automatically. The function is called with the
arguments args
, but any missing arguments are obtained from
autoArgs
. This function is intended to be partially
parameterised, e.g.,
callPackage = callPackageWith pkgs;
pkgs = {
libfoo = callPackage ./foo.nix { };
libbar = callPackage ./bar.nix { };
};
If the libbar
function expects an argument named libfoo
, it is
automatically passed as an argument. Overrides or missing
arguments can be supplied in args
, e.g.
libbar = callPackage ./bar.nix {
libfoo = null;
enableX11 = true;
};
autoArgs
1. Function argument
fn
2. Function argument
args
3. Function argument
callPackageWith :: AttrSet -> ((AttrSet -> a) | Path) -> AttrSet -> a
Located at lib/customisation.nix:212 in <nixpkgs>
.
lib.customisation.callPackagesWith
Like callPackage, but for a function that returns an attribute set of derivations. The override function is added to the individual attributes.
autoArgs
1. Function argument
fn
2. Function argument
args
3. Function argument
callPackagesWith :: AttrSet -> ((AttrSet -> AttrSet) | Path) -> AttrSet -> AttrSet
Located at lib/customisation.nix:298 in <nixpkgs>
.
lib.customisation.extendDerivation
Add attributes to each output of a derivation without changing the derivation itself and check a given condition when evaluating.
condition
1. Function argument
passthru
2. Function argument
drv
3. Function argument
extendDerivation :: Bool -> Any -> Derivation -> Derivation
Located at lib/customisation.nix:339 in <nixpkgs>
.
lib.customisation.hydraJob
Strip a derivation of all non-essential attributes, returning only those needed by hydra-eval-jobs. Also strictly evaluate the result to ensure that there are no thunks kept alive to prevent garbage collection.
drv
1. Function argument
hydraJob :: (Derivation | Null) -> (Derivation | Null)
Located at lib/customisation.nix:388 in <nixpkgs>
.
lib.customisation.makeScope
Make an attribute set (a “scope”) from functions that take arguments from that same attribute set. See Example 247 for how to use it.
newScope
(AttrSet -> ((AttrSet -> a) | Path) -> AttrSet -> a
)
A function that takes an attribute set attrs
and returns what ends up as callPackage
in the output.
Typical values are callPackageWith
or the output attribute newScope
.
f
(AttrSet -> AttrSet
)
A function that takes an attribute set as returned by makeScope newScope f
(a “scope”) and returns any attribute set.
This function is used to compute the fixpoint of the resulting scope using callPackage
.
Its argument is the lazily evaluated reference to the value of that fixpoint, and is typically called self
or final
.
See Example 247 for how to use it. See the section called “lib.fixedPoints: explicit recursion functions” for details on fixpoint computation.
makeScope
returns an attribute set of a form called scope
, which also contains the final attributes produced by f
:
scope :: {
callPackage :: ((AttrSet -> a) | Path) -> AttrSet -> a
newScope = AttrSet -> scope
overrideScope = (scope -> scope -> AttrSet) -> scope
packages :: AttrSet -> AttrSet
}
callPackage
(((AttrSet -> a) | Path) -> AttrSet -> a
)
A function that
Takes a function p
, or a path to a Nix file that contains a function p
, which takes an attribute set and returns value of arbitrary type a
,
Takes an attribute set args
with explicit attributes to pass to p
,
Calls f
with attributes from the original attribute set attrs
passed to newScope
updated with args
, i.e. attrs // args
, if they match the attributes in the argument of p
.
All such functions p
will be called with the same value for attrs
.
See Example 248 for how to use it.
newScope
(AttrSet -> scope
)
Takes an attribute set attrs
and returns a scope that extends the original scope.
overrideScope
((scope -> scope -> AttrSet) -> scope
)
Takes a function g
of the form final: prev: { # attributes }
to act as an overlay on f
, and returns a new scope with values determined by extends g f
.
See for details.
This allows subsequent modification of the final attribute set in a consistent way, i.e. all functions p
invoked with callPackage
will be called with the modified values.
packages
(AttrSet -> AttrSet
)
The value of the argument f
to makeScope
.
final attributes
The final values returned by f
.
pkgs
The functions in foo.nix
and bar.nix
can depend on each other, in the sense that foo.nix
can contain a function that expects bar
as an attribute in its argument.
let
pkgs = import <nixpkgs> { };
in
pkgs.lib.makeScope pkgs.newScope (self: {
foo = self.callPackage ./foo.nix { };
bar = self.callPackage ./bar.nix { };
})
evaluates to
{
callPackage = «lambda»;
newScope = «lambda»;
overrideScope = «lambda»;
packages = «lambda»;
foo = «derivation»;
bar = «derivation»;
}
callPackage
from a scopelet
pkgs = import <nixpkgs> { };
inherit (pkgs) lib;
scope = lib.makeScope lib.callPackageWith (self: { a = 1; b = 2; });
three = scope.callPackage ({ a, b }: a + b) { };
four = scope.callPackage ({ a, b }: a + b) { a = 2; };
in
[ three four ]
evaluates to
[ 3 4 ]
makeScope :: (AttrSet -> ((AttrSet -> a) | Path) -> AttrSet -> a) -> (AttrSet -> AttrSet) -> scope
Located at lib/customisation.nix:541 in <nixpkgs>
.
lib.customisation.makeScopeWithSplicing
backward compatibility with old uncurried form; deprecated
splicePackages
1. Function argument
newScope
2. Function argument
otherSplices
3. Function argument
keep
4. Function argument
extra
5. Function argument
f
6. Function argument
Located at lib/customisation.nix:584 in <nixpkgs>
.
lib.customisation.makeScopeWithSplicing'
Like makeScope, but aims to support cross compilation. It’s still ugly, but hopefully it helps a little bit.
makeScopeWithSplicing' ::
{ splicePackages :: Splice -> AttrSet
, newScope :: AttrSet -> ((AttrSet -> a) | Path) -> AttrSet -> a
}
-> { otherSplices :: Splice, keep :: AttrSet -> AttrSet, extra :: AttrSet -> AttrSet }
-> AttrSet
Splice ::
{ pkgsBuildBuild :: AttrSet
, pkgsBuildHost :: AttrSet
, pkgsBuildTarget :: AttrSet
, pkgsHostHost :: AttrSet
, pkgsHostTarget :: AttrSet
, pkgsTargetTarget :: AttrSet
}
Located at lib/customisation.nix:614 in <nixpkgs>
.
Some functions for manipulating meta attributes, as well as the name attribute.
lib.meta.addMetaAttrs
Add to or override the meta attributes of the given derivation.
newAttrs
1. Function argument
drv
2. Function argument
lib.meta.addMetaAttrs
usage exampleaddMetaAttrs {description = "Bla blah";} somePkg
Located at lib/meta.nix:42 in <nixpkgs>
.
lib.meta.dontDistribute
Disable Hydra builds of given derivation.
lib.meta.setName
Change the symbolic name of a derivation.
Dependent derivations will be rebuilt when the symbolic name is changed.
lib.meta.updateName
Like setName
, but takes the previous name as an argument.
updater
1. Function argument
drv
2. Function argument
lib.meta.updateName
usage exampleupdateName (oldName: oldName + "-experimental") somePkg
Located at lib/meta.nix:102 in <nixpkgs>
.
lib.meta.appendToName
Append a suffix to the name of a package (before the version part).
lib.meta.mapDerivationAttrset
Apply a function to each derivation and only to derivations in an attrset.
lib.meta.defaultPriority
The default priority of packages in Nix. See defaultPriority
in src/nix/profile.cc
.
Located at lib/meta.nix:138 in <nixpkgs>
.
lib.meta.setPrio
Set the nix-env priority of the package. Note that higher values are lower priority, and vice versa.
priority
1. The priority to set.
drv
2. Function argument
Located at lib/meta.nix:151 in <nixpkgs>
.
lib.meta.lowPrio
Decrease the nix-env priority of the package, i.e., other versions/variants of the package will be preferred.
lib.meta.lowPrioSet
Apply lowPrio to an attrset with derivations.
lib.meta.hiPrio
Increase the nix-env priority of the package, i.e., this version/variant of the package will be preferred.
lib.meta.hiPrioSet
Apply hiPrio to an attrset with derivations.
lib.meta.platformMatch
Check to see if a platform is matched by the given meta.platforms
element.
A meta.platform
pattern is either
(legacy) a system string.
(modern) a pattern for the entire platform structure (see lib.systems.inspect.platformPatterns
).
(modern) a pattern for the platform parsed
field (see lib.systems.inspect.patterns
).
We can inject these into a pattern for the whole of a structured platform, and then match that.
platform
1. Function argument
elem
2. Function argument
lib.meta.platformMatch
usage examplelib.meta.platformMatch { system = "aarch64-darwin"; } "aarch64-darwin"
=> true
Located at lib/meta.nix:240 in <nixpkgs>
.
lib.meta.availableOn
Check if a package is available on a given platform.
A package is available on a platform if both
One of meta.platforms
pattern matches the given
platform, or meta.platforms
is not present.
None of meta.badPlatforms
pattern matches the given platform.
platform
1. Function argument
pkg
2. Function argument
lib.meta.availableOn
usage examplelib.meta.availableOn { system = "aarch64-darwin"; } pkg.zsh
=> true
Located at lib/meta.nix:289 in <nixpkgs>
.
lib.meta.licensesSpdx
Mapping of SPDX ID to the attributes in lib.licenses.
For SPDX IDs, see https://spdx.org/licenses. Note that some SPDX licenses might be missing.
lib.meta.licensesSpdx
usage examplelib.licensesSpdx.MIT == lib.licenses.mit
=> true
lib.licensesSpdx."MY LICENSE"
=> error: attribute 'MY LICENSE' missing
Located at lib/meta.nix:312 in <nixpkgs>
.
lib.meta.getLicenseFromSpdxId
Get the corresponding attribute in lib.licenses from the SPDX ID
or warn and fallback to { shortName = <license string>; }
.
For SPDX IDs, see https://spdx.org/licenses. Note that some SPDX licenses might be missing.
getLicenseFromSpdxId :: str -> AttrSet
lib.meta.getLicenseFromSpdxId
usage examplelib.getLicenseFromSpdxId "MIT" == lib.licenses.mit
=> true
lib.getLicenseFromSpdxId "mIt" == lib.licenses.mit
=> true
lib.getLicenseFromSpdxId "MY LICENSE"
=> trace: warning: getLicenseFromSpdxId: No license matches the given SPDX ID: MY LICENSE
=> { shortName = "MY LICENSE"; }
Located at lib/meta.nix:349 in <nixpkgs>
.
lib.meta.getLicenseFromSpdxIdOr
Get the corresponding attribute in lib.licenses from the SPDX ID or fallback to the given default value.
For SPDX IDs, see https://spdx.org/licenses. Note that some SPDX licenses might be missing.
licstr
1. SPDX ID string to find a matching license
default
2. Fallback value when a match is not found
getLicenseFromSpdxIdOr :: str -> Any -> Any
lib.meta.getLicenseFromSpdxIdOr
usage examplelib.getLicenseFromSpdxIdOr "MIT" null == lib.licenses.mit
=> true
lib.getLicenseFromSpdxId "mIt" null == lib.licenses.mit
=> true
lib.getLicenseFromSpdxIdOr "MY LICENSE" lib.licenses.free == lib.licenses.free
=> true
lib.getLicenseFromSpdxIdOr "MY LICENSE" null
=> null
lib.getLicenseFromSpdxIdOr "MY LICENSE" (builtins.throw "No SPDX ID matches MY LICENSE")
=> error: No SPDX ID matches MY LICENSE
Located at lib/meta.nix:395 in <nixpkgs>
.
lib.meta.getExe
Get the path to the main program of a package based on meta.mainProgram
x
1. Function argument
getExe :: package -> string
lib.meta.getExe
usage examplegetExe pkgs.hello
=> "/nix/store/g124820p9hlv4lj8qplzxw1c44dxaw1k-hello-2.12/bin/hello"
getExe pkgs.mustache-go
=> "/nix/store/am9ml4f4ywvivxnkiaqwr0hyxka1xjsf-mustache-go-1.3.0/bin/mustache"
Located at lib/meta.nix:433 in <nixpkgs>
.
lib.meta.getExe'
Get the path of a program of a derivation.
x
1. Function argument
y
2. Function argument
getExe' :: derivation -> string -> string
lib.meta.getExe'
usage examplegetExe' pkgs.hello "hello"
=> "/nix/store/g124820p9hlv4lj8qplzxw1c44dxaw1k-hello-2.12/bin/hello"
getExe' pkgs.imagemagick "convert"
=> "/nix/store/5rs48jamq7k6sal98ymj9l4k2bnwq515-imagemagick-7.1.1-15/bin/convert"
Located at lib/meta.nix:473 in <nixpkgs>
.
lib.derivations.lazyDerivation
Restrict a derivation to a predictable set of attribute names, so that the returned attrset is not strict in the actual derivation, saving a lot of computation when the derivation is non-trivial.
This is useful in situations where a derivation might only be used for its passthru attributes, improving evaluation performance.
The returned attribute set is lazy in derivation
. Specifically, this
means that the derivation will not be evaluated in at least the
situations below.
For illustration and/or testing, we define derivation such that its evaluation is very noticeable.
let derivation = throw "This won't be evaluated.";
In the following expressions, derivation
will not be evaluated:
(lazyDerivation { inherit derivation; }).type
attrNames (lazyDerivation { inherit derivation; })
(lazyDerivation { inherit derivation; } // { foo = true; }).foo
(lazyDerivation { inherit derivation; meta.foo = true; }).meta
In these expressions, derivation
will be evaluated:
"${lazyDerivation { inherit derivation }}"
(lazyDerivation { inherit derivation }).outPath
(lazyDerivation { inherit derivation }).meta
And the following expressions are not valid, because the refer to implementation details and/or attributes that may not be present on some derivations:
(lazyDerivation { inherit derivation }).buildInputs
(lazyDerivation { inherit derivation }).passthru
(lazyDerivation { inherit derivation }).pythonPath
Takes an attribute set with the following attributes
derivation
The derivation to be wrapped.
meta
Optional meta attribute.
While this function is primarily about derivations, it can improve
the meta
package attribute, which is usually specified through
mkDerivation
.
passthru
Optional extra values to add to the returned attrset.
This can be used for adding package attributes, such as tests
.
outputs
Optional list of assumed outputs. Default: [“out”]
This must match the set of outputs that the returned derivation has. You must use this when the derivation has multiple outputs.
Located at lib/derivations.nix:90 in <nixpkgs>
.
lib.derivations.optionalDrvAttr
Conditionally set a derivation attribute.
Because mkDerivation
sets __ignoreNulls = true
, a derivation
attribute set to null
will not impact the derivation output hash.
Thus, this function passes through its value
argument if the cond
is true
, but returns null
if not.
cond
Condition
value
Attribute value
optionalDrvAttr :: Bool -> a -> a | Null
lib.derivations.optionalDrvAttr
usage example(stdenv.mkDerivation {
name = "foo";
x = optionalDrvAttr true 1;
y = optionalDrvAttr false 1;
}).drvPath == (stdenv.mkDerivation {
name = "foo";
x = 1;
}).drvPath
=> true
Located at lib/derivations.nix:206 in <nixpkgs>
.
Generators are functions that create file formats from nix data structures, e. g. for configuration files. There are generators available for: INI
, JSON
and YAML
All generators follow a similar call interface: generatorName configFunctions data
, where configFunctions
is an attrset of user-defined functions that format nested parts of the content. They each have common defaults, so often they do not need to be set manually. An example is mkSectionName ? (name: libStr.escape [ "[" "]" ] name)
from the INI
generator. It receives the name of a section and sanitizes it. The default mkSectionName
escapes [
and ]
with a backslash.
Generators can be fine-tuned to produce exactly the file format required by your application/service. One example is an INI-file format which uses :
as separator, the strings "yes"
/"no"
as boolean values and requires all string values to be quoted:
let
inherit (lib) generators isString;
customToINI = generators.toINI {
# specifies how to format a key/value pair
mkKeyValue = generators.mkKeyValueDefault {
# specifies the generated string for a subset of nix values
mkValueString = v:
if v == true then ''"yes"''
else if v == false then ''"no"''
else if isString v then ''"${v}"''
# and delegates all other values to the default generator
else generators.mkValueStringDefault {} v;
} ":";
};
# the INI file can now be given as plain old nix values
in customToINI {
main = {
pushinfo = true;
autopush = false;
host = "localhost";
port = 42;
};
mergetool = {
merge = "diff3";
};
}
This will produce the following INI file as nix string:
[main]
autopush:"no"
host:"localhost"
port:42
pushinfo:"yes"
str\:ange:"very::strange"
[mergetool]
merge:"diff3"
Nix store paths can be converted to strings by enclosing a derivation attribute like so: "${drv}"
.
Detailed documentation for each generator can be found here
Nix is a unityped, dynamic language, this means every value can potentially appear anywhere. Since it is also non-strict, evaluation order and what ultimately is evaluated might surprise you. Therefore it is important to be able to debug nix expressions.
In the lib/debug.nix
file you will find a number of functions that help (pretty-)printing values while evaluation is running. You can even specify how deep these values should be printed recursively, and transform them on the fly. Please consult the docstrings in lib/debug.nix
for usage information.
prefer-remote-fetch
is an overlay that download sources on remote builder. This is useful when the evaluating machine has a slow upload while the builder can fetch faster directly from the source. To use it, put the following snippet as a new overlay:
self: super:
(super.prefer-remote-fetch self super)
A full configuration example for that sets the overlay up for your own account, could look like this
$ mkdir ~/.config/nixpkgs/overlays/
$ cat > ~/.config/nixpkgs/overlays/prefer-remote-fetch.nix <<EOF
self: super: super.prefer-remote-fetch self super
EOF
pkgs.nix-gitignore
is a function that acts similarly to builtins.filterSource
but also allows filtering with the help of the gitignore format.
pkgs.nix-gitignore
exports a number of functions, but you’ll most likely need either gitignoreSource
or gitignoreSourcePure
. As their first argument, they both accept either 1. a file with gitignore lines or 2. a string with gitignore lines, or 3. a list of either of the two. They will be concatenated into a single big string.
{ pkgs ? import <nixpkgs> {} }: {
src = nix-gitignore.gitignoreSource [] ./source;
# Simplest version
src = nix-gitignore.gitignoreSource "supplemental-ignores\n" ./source;
# This one reads the ./source/.gitignore and concats the auxiliary ignores
src = nix-gitignore.gitignoreSourcePure "ignore-this\nignore-that\n" ./source;
# Use this string as gitignore, don't read ./source/.gitignore.
src = nix-gitignore.gitignoreSourcePure ["ignore-this\nignore-that\n" ~/.gitignore] ./source;
# It also accepts a list (of strings and paths) that will be concatenated
# once the paths are turned to strings via readFile.
}
These functions are derived from the Filter
functions by setting the first filter argument to (_: _: true)
:
{
gitignoreSourcePure = gitignoreFilterSourcePure (_: _: true);
gitignoreSource = gitignoreFilterSource (_: _: true);
}
Those filter functions accept the same arguments the builtins.filterSource
function would pass to its filters, thus fn: gitignoreFilterSourcePure fn ""
should be extensionally equivalent to filterSource
. The file is blacklisted if it’s blacklisted by either your filter or the gitignoreFilter.
If you want to make your own filter from scratch, you may use
{
gitignoreFilter = ign: root: filterPattern (gitignoreToPatterns ign) root;
}
If you wish to use a filter that would search for .gitignore files in subdirectories, just like git does by default, use this function:
{
# gitignoreFilterRecursiveSource = filter: patterns: root:
# OR
gitignoreRecursiveSource = gitignoreFilterSourcePure (_: _: true);
}
Table of Contents
The module system is a language for handling configuration, implemented as a Nix library.
Compared to plain Nix, it adds documentation, type checking and composition or extensibility.
This chapter is new and not complete yet. For a gentle introduction to the module system, in the context of NixOS, see Writing NixOS Modules in the NixOS manual.
lib.evalModules
Evaluate a set of modules. This function is typically only used once per application (e.g. once in NixOS, once in Home Manager, …).
modules
A list of modules. These are merged together to form the final configuration.
specialArgs
An attribute set of module arguments that can be used in imports
.
This is in contrast to config._module.args
, which is only available after all imports
have been resolved.
class
If the class
attribute is set and non-null
, the module system will reject imports
with a different _class
declaration.
The class
value should be a string in lower camel case.
If applicable, the class
should match the “prefix” of the attributes used in (experimental) flakes. Some examples are:
nixos
as in flake.nixosModules
nixosTest
: modules that constitute a NixOS VM test
prefix
A list of strings representing the location at or below which all options are evaluated. This is used by types.submodule
to improve error reporting and find the implicit name
module argument.
The result is an attribute set with the following attributes:
options
The nested attribute set of all option declarations.
config
The nested attribute set of all option values.
type
A module system type. This type is an instance of types.submoduleWith
containing the current modules
.
The option definitions that are typed with this type will extend the current set of modules, like extendModules
.
However, the value returned from the type is just the config
, like any submodule.
If you’re familiar with prototype inheritance, you can think of this evalModules
invocation as the prototype, and usages of this type as the instances.
This type is also available to the modules
as the module argument moduleType
.
extendModules
A function similar to evalModules
but building on top of the already passed modules
. Its arguments, modules
and specialArgs
are added to the existing values.
If you’re familiar with prototype inheritance, you can think of the current, actual evalModules
invocation as the prototype, and the return value of extendModules
as the instance.
This functionality is also available to modules as the extendModules
module argument.
Evaluation Performance
extendModules
returns a configuration that shares very little with the original evalModules
invocation, because the module arguments may be different.
So if you have a configuration that has been (or will be) largely evaluated, almost none of the computation is shared with the configuration returned by extendModules
.
The real work of module evaluation happens while computing the values in config
and options
, so multiple invocations of extendModules
have a particularly small cost, as long as only the final config
and options
are evaluated.
If you do reference multiple config
(or options
) from before and after extendModules
, evaluation performance is the same as with multiple evalModules
invocations, because the new modules’ ability to override existing configuration fundamentally requires constructing a new config
and options
fixpoint.
_module
A portion of the configuration tree which is elided from config
.
_type
A nominal type marker, always "configuration"
.
class
The class
argument.
Table of Contents
The standard build environment in the Nix Packages collection provides an environment for building Unix packages that does a lot of common build tasks automatically. In fact, for Unix packages that use the standard ./configure; make; make install
build interface, you don’t need to write a build script at all; the standard environment does everything automatically. If stdenv
doesn’t do what you need automatically, you can easily customise or override the various build phases.
stdenv
To build a package with the standard environment, you use the function stdenv.mkDerivation
, instead of the primitive built-in function derivation
, e.g.
stdenv.mkDerivation {
name = "libfoo-1.2.3";
src = fetchurl {
url = "http://example.org/libfoo-1.2.3.tar.bz2";
hash = "sha256-tWxU/LANbQE32my+9AXyt3nCT7NBVfJ45CX757EMT3Q=";
};
}
(stdenv
needs to be in scope, so if you write this in a separate Nix expression from pkgs/all-packages.nix
, you need to pass it as a function argument.) Specifying a name
and a src
is the absolute minimum Nix requires. For convenience, you can also use pname
and version
attributes and mkDerivation
will automatically set name
to "${pname}-${version}"
by default.
Since RFC 0035, this is preferred for packages in Nixpkgs, as it allows us to reuse the version easily:
stdenv.mkDerivation rec {
pname = "libfoo";
version = "1.2.3";
src = fetchurl {
url = "http://example.org/libfoo-source-${version}.tar.bz2";
hash = "sha256-tWxU/LANbQE32my+9AXyt3nCT7NBVfJ45CX757EMT3Q=";
};
}
Many packages have dependencies that are not provided in the standard environment. It’s usually sufficient to specify those dependencies in the buildInputs
attribute:
stdenv.mkDerivation {
pname = "libfoo";
version = "1.2.3";
# ...
buildInputs = [libbar perl ncurses];
}
This attribute ensures that the bin
subdirectories of these packages appear in the PATH
environment variable during the build, that their include
subdirectories are searched by the C compiler, and so on. (See the section called “Package setup hooks” for details.)
Often it is necessary to override or modify some aspect of the build. To make this easier, the standard environment breaks the package build into a number of phases, all of which can be overridden or modified individually: unpacking the sources, applying patches, configuring, building, and installing. (There are some others; see the section called “Phases”.) For instance, a package that doesn’t supply a makefile but instead has to be compiled “manually” could be handled like this:
stdenv.mkDerivation {
pname = "fnord";
version = "4.5";
# ...
buildPhase = ''
gcc foo.c -o foo
'';
installPhase = ''
mkdir -p $out/bin
cp foo $out/bin
'';
}
(Note the use of ''
-style string literals, which are very convenient for large multi-line script fragments because they don’t need escaping of "
and \
, and because indentation is intelligently removed.)
There are many other attributes to customise the build. These are listed in the section called “Attributes”.
While the standard environment provides a generic builder, you can still supply your own build script:
stdenv.mkDerivation {
pname = "libfoo";
version = "1.2.3";
# ...
builder = ./builder.sh;
}
where the builder can do anything it wants, but typically starts with
source $stdenv/setup
to let stdenv
set up the environment (e.g. by resetting PATH
and populating it from build inputs). If you want, you can still use stdenv
’s generic builder:
source $stdenv/setup
buildPhase() {
echo "... this is my custom build phase ..."
gcc foo.c -o foo
}
installPhase() {
mkdir -p $out/bin
cp foo $out/bin
}
genericBuild
stdenv
package in nix-shell
To build a stdenv
package in a nix-shell
, enter a shell, find the phases you wish to build, then invoke genericBuild
manually:
Go to an empty directory, invoke nix-shell
with the desired package, and from inside the shell, set the output variables to a writable directory:
cd "$(mktemp -d)"
nix-shell '<nixpkgs>' -A some_package
export out=$(pwd)/out
Next, invoke the desired parts of the build. First, run the phases that generate a working copy of the sources, which will change directory to the sources for you:
phases="${prePhases[*]:-} unpackPhase patchPhase" genericBuild
Then, run more phases up until the failure is reached. If the failure is in the build or check phase, the following phases would be required:
phases="${preConfigurePhases[*]:-} configurePhase ${preBuildPhases[*]:-} buildPhase checkPhase" genericBuild
Use this command to run all install phases:
phases="${preInstallPhases[*]:-} installPhase ${preFixupPhases[*]:-} fixupPhase installCheckPhase" genericBuild
Single phase can be re-run as many times as necessary to examine the failure like so:
phases="buildPhase" genericBuild
To modify a phase, first print it with
echo "$buildPhase"
Or, if that is empty, for instance, if it is using a function:
type buildPhase
then change it in a text editor, and paste it back to the terminal.
This method may have some inconsistencies in environment variables and behaviour compared to a normal build within the Nix build sandbox. The following is a non-exhaustive list of such differences:
TMP
, TMPDIR
, and similar variables likely point to non-empty directories that the build might conflict with files in.
Output store paths are not writable, so the variables for outputs need to be overridden to writable paths.
Other environment variables may be inconsistent with a nix-build
either due to nix-shell
’s initialization script or due to the use of nix-shell
without the --pure
option.
If the build fails differently inside the shell than in the sandbox, consider using breakpointHook
and invoking nix-build
instead.
The --keep-failed
option for nix-build
may also be useful to examine the build directory of a failed build.
stdenv
The standard environment provides the following packages:
The GNU C Compiler, configured with C and C++ support.
GNU coreutils (contains a few dozen standard Unix commands).
GNU findutils (contains find
).
GNU diffutils (contains diff
, cmp
).
GNU sed
.
GNU grep
.
GNU awk
.
GNU tar
.
gzip
, bzip2
and xz
.
GNU Make.
Bash. This is the shell used for all builders in the Nix Packages collection. Not using /bin/sh
removes a large source of portability problems.
The patch
command.
On Linux, stdenv
also includes the patchelf
utility.
Build systems often require more dependencies than just what stdenv
provides. This section describes attributes accepted by stdenv.mkDerivation
that can be used to make these dependencies available to the build system.
A full reference of the different kinds of dependencies is provided in the section called “Reference”, but here is an overview of the most common ones. It should cover most use cases.
Add dependencies to nativeBuildInputs
if they are executed during the build:
those which are needed on $PATH
during the build, for example cmake
and pkg-config
setup hooks, for example makeWrapper
interpreters needed by patchShebangs
for build scripts (with the --build
flag), which can be the case for e.g. perl
Add dependencies to buildInputs
if they will end up copied or linked into the final output or otherwise used at runtime:
libraries used by compilers, for example zlib
,
interpreters needed by patchShebangs
for scripts which are installed, which can be the case for e.g. perl
These criteria are independent.
For example, software using Wayland usually needs the wayland
library at runtime, so wayland
should be added to buildInputs
.
But it also executes the wayland-scanner
program as part of the build to generate code, so wayland
should also be added to nativeBuildInputs
.
Dependencies needed only to run tests are similarly classified between native (executed during build) and non-native (executed at runtime):
nativeCheckInputs
for test tools needed on $PATH
(such as ctest
) and setup hooks (for example pytestCheckHook
)
checkInputs
for libraries linked into test executables (for example the qcheck
OCaml package)
These dependencies are only injected when doCheck
is set to true
.
Consider for example this simplified derivation for solo5
, a sandboxing tool:
stdenv.mkDerivation rec {
pname = "solo5";
version = "0.7.5";
src = fetchurl {
url = "https://github.com/Solo5/solo5/releases/download/v${version}/solo5-v${version}.tar.gz";
hash = "sha256-viwrS9lnaU8sTGuzK/+L/PlMM/xRRtgVuK5pixVeDEw=";
};
nativeBuildInputs = [ makeWrapper pkg-config ];
buildInputs = [ libseccomp ];
postInstall = ''
substituteInPlace $out/bin/solo5-virtio-mkimage \
--replace-fail "/usr/lib/syslinux" "${syslinux}/share/syslinux" \
--replace-fail "/usr/share/syslinux" "${syslinux}/share/syslinux" \
--replace-fail "cp " "cp --no-preserve=mode "
wrapProgram $out/bin/solo5-virtio-mkimage \
--prefix PATH : ${lib.makeBinPath [ dosfstools mtools parted syslinux ]}
'';
doCheck = true;
nativeCheckInputs = [ util-linux qemu ];
checkPhase = '' [elided] '';
}
makeWrapper
is a setup hook, i.e., a shell script sourced by the generic builder of stdenv
.
It is thus executed during the build and must be added to nativeBuildInputs
.
pkg-config
is a build tool which the configure script of solo5
expects to be on $PATH
during the build:
therefore, it must be added to nativeBuildInputs
.
libseccomp
is a library linked into $out/bin/solo5-elftool
.
As it is used at runtime, it must be added to buildInputs
.
Tests need qemu
and getopt
(from util-linux
) on $PATH
, these must be added to nativeCheckInputs
.
Some dependencies are injected directly in the shell code of phases: syslinux
, dosfstools
, mtools
, and parted
.
In this specific case, they will end up in the output of the derivation ($out
here).
As Nix marks dependencies whose absolute path is present in the output as runtime dependencies, adding them to buildInputs
is not required.
For more complex cases, like libraries linked into an executable which is then executed as part of the build system, see the section called “Reference”.
As described in the Nix manual, almost any *.drv
store path in a derivation’s attribute set will induce a dependency on that derivation. mkDerivation
, however, takes a few attributes intended to include all the dependencies of a package. This is done both for structure and consistency, but also so that certain other setup can take place. For example, certain dependencies need their bin directories added to the PATH
. That is built-in, but other setup is done via a pluggable mechanism that works in conjunction with these dependency attributes. See the section called “Package setup hooks” for details.
Dependencies can be broken down along these axes: their host and target platforms relative to the new derivation’s. The platform distinctions are motivated by cross compilation; see Cross-compilation for exactly what each platform means. [1] But even if one is not cross compiling, the platforms imply whether a dependency is needed at run-time or build-time.
The extension of PATH
with dependencies, alluded to above, proceeds according to the relative platforms alone. The process is carried out only for dependencies whose host platform matches the new derivation’s build platform i.e. dependencies which run on the platform where the new derivation will be built. [2] For each dependency <dep> of those dependencies, dep/bin
, if present, is added to the PATH
environment variable.
Propagated dependencies are made available to all downstream dependencies. This is particularly useful for interpreted languages, where all transitive dependencies have to be present in the same environment. Therefore it is used for the Python infrastructure in Nixpkgs.
Propagated dependencies should be used with care, because they obscure the actual build inputs of dependent derivations and cause side effects through setup hooks. This can lead to conflicting dependencies that cannot easily be resolved.
with import <nixpkgs> {};
let
bar = stdenv.mkDerivation {
name = "bar";
dontUnpack = true;
# `hello` is also made available to dependents, such as `foo`
propagatedBuildInputs = [ hello ];
postInstall = "mkdir $out";
};
foo = stdenv.mkDerivation {
name = "foo";
dontUnpack = true;
# `bar` is a direct dependency, which implicitly includes the propagated `hello`
buildInputs = [ bar ];
# The `hello` binary is available!
postInstall = "hello > $out";
};
in
foo
Dependency propagation takes cross compilation into account, meaning that dependencies that cross platform boundaries are properly adjusted.
To determine the exact rules for dependency propagation, we start by assigning to each dependency a couple of ternary numbers (-1
for build
, 0
for host
, and 1
for target
) representing its dependency type, which captures how its host and target platforms are each “offset” from the depending derivation’s host and target platforms. The following table summarize the different combinations that can be obtained:
host → target | attribute name | offset |
---|---|---|
build --> build | depsBuildBuild | -1, -1 |
build --> host | nativeBuildInputs | -1, 0 |
build --> target | depsBuildTarget | -1, 1 |
host --> host | depsHostHost | 0, 0 |
host --> target | buildInputs | 0, 1 |
target --> target | depsTargetTarget | 1, 1 |
Algorithmically, we traverse propagated inputs, accumulating every propagated dependency’s propagated dependencies and adjusting them to account for the “shift in perspective” described by the current dependency’s platform offsets. This results is sort of a transitive closure of the dependency relation, with the offsets being approximately summed when two dependency links are combined. We also prune transitive dependencies whose combined offsets go out-of-bounds, which can be viewed as a filter over that transitive closure removing dependencies that are blatantly absurd.
We can define the process precisely with Natural Deduction using the inference rules. This probably seems a bit obtuse, but so is the bash code that actually implements it! [3] They’re confusing in very different ways so… hopefully if something doesn’t make sense in one presentation, it will in the other!
let mapOffset(h, t, i) = i + (if i <= 0 then h else t - 1)
propagated-dep(h0, t0, A, B)
propagated-dep(h1, t1, B, C)
h0 + h1 in {-1, 0, 1}
h0 + t1 in {-1, 0, 1}
-------------------------------------- Transitive property
propagated-dep(mapOffset(h0, t0, h1),
mapOffset(h0, t0, t1),
A, C)
let mapOffset(h, t, i) = i + (if i <= 0 then h else t - 1)
dep(h0, t0, A, B)
propagated-dep(h1, t1, B, C)
h0 + h1 in {-1, 0, 1}
h0 + t1 in {-1, 0, -1}
----------------------------- Take immediate dependencies' propagated dependencies
propagated-dep(mapOffset(h0, t0, h1),
mapOffset(h0, t0, t1),
A, C)
propagated-dep(h, t, A, B)
----------------------------- Propagated dependencies count as dependencies
dep(h, t, A, B)
Some explanation of this monstrosity is in order. In the common case, the target offset of a dependency is the successor to the target offset: t = h + 1
. That means that:
let f(h, t, i) = i + (if i <= 0 then h else t - 1)
let f(h, h + 1, i) = i + (if i <= 0 then h else (h + 1) - 1)
let f(h, h + 1, i) = i + (if i <= 0 then h else h)
let f(h, h + 1, i) = i + h
This is where “sum-like” comes in from above: We can just sum all of the host offsets to get the host offset of the transitive dependency. The target offset is the transitive dependency is the host offset + 1, just as it was with the dependencies composed to make this transitive one; it can be ignored as it doesn’t add any new information.
Because of the bounds checks, the uncommon cases are h = t
and h + 2 = t
. In the former case, the motivation for mapOffset
is that since its host and target platforms are the same, no transitive dependency of it should be able to “discover” an offset greater than its reduced target offsets. mapOffset
effectively “squashes” all its transitive dependencies’ offsets so that none will ever be greater than the target offset of the original h = t
package. In the other case, h + 1
is skipped over between the host and target offsets. Instead of squashing the offsets, we need to “rip” them apart so no transitive dependencies’ offset is that one.
Overall, the unifying theme here is that propagation shouldn’t be introducing transitive dependencies involving platforms the depending package is unaware of. [One can imagine the depending package asking for dependencies with the platforms it knows about; other platforms it doesn’t know how to ask for. The platform description in that scenario is a kind of unforgeable capability.] The offset bounds checking and definition of mapOffset
together ensure that this is the case. Discovering a new offset is discovering a new platform, and since those platforms weren’t in the derivation “spec” of the needing package, they cannot be relevant. From a capability perspective, we can imagine that the host and target platforms of a package are the capabilities a package requires, and the depending package must provide the capability to the dependency.
depsBuildBuild
A list of dependencies whose host and target platforms are the new derivation’s build platform. These are programs and libraries used at build time that produce programs and libraries also used at build time. If the dependency doesn’t care about the target platform (i.e. isn’t a compiler or similar tool), put it in nativeBuildInputs
instead. The most common use of this buildPackages.stdenv.cc
, the default C compiler for this role. That example crops up more than one might think in old commonly used C libraries.
Since these packages are able to be run at build-time, they are always added to the PATH
, as described above. But since these packages are only guaranteed to be able to run then, they shouldn’t persist as run-time dependencies. This isn’t currently enforced, but could be in the future.
nativeBuildInputs
A list of dependencies whose host platform is the new derivation’s build platform, and target platform is the new derivation’s host platform. These are programs and libraries used at build-time that, if they are a compiler or similar tool, produce code to run at run-time—i.e. tools used to build the new derivation. If the dependency doesn’t care about the target platform (i.e. isn’t a compiler or similar tool), put it here, rather than in depsBuildBuild
or depsBuildTarget
. This could be called depsBuildHost
but nativeBuildInputs
is used for historical continuity.
Since these packages are able to be run at build-time, they are added to the PATH
, as described above. But since these packages are only guaranteed to be able to run then, they shouldn’t persist as run-time dependencies. This isn’t currently enforced, but could be in the future.
depsBuildTarget
A list of dependencies whose host platform is the new derivation’s build platform, and target platform is the new derivation’s target platform. These are programs used at build time that produce code to run with code produced by the depending package. Most commonly, these are tools used to build the runtime or standard library that the currently-being-built compiler will inject into any code it compiles. In many cases, the currently-being-built-compiler is itself employed for that task, but when that compiler won’t run (i.e. its build and host platform differ) this is not possible. Other times, the compiler relies on some other tool, like binutils, that is always built separately so that the dependency is unconditional.
This is a somewhat confusing concept to wrap one’s head around, and for good reason. As the only dependency type where the platform offsets, -1
and 1
, are not adjacent integers, it requires thinking of a bootstrapping stage two away from the current one. It and its use-case go hand in hand and are both considered poor form: try to not need this sort of dependency, and try to avoid building standard libraries and runtimes in the same derivation as the compiler produces code using them. Instead strive to build those like a normal library, using the newly-built compiler just as a normal library would. In short, do not use this attribute unless you are packaging a compiler and are sure it is needed.
Since these packages are able to run at build time, they are added to the PATH
, as described above. But since these packages are only guaranteed to be able to run then, they shouldn’t persist as run-time dependencies. This isn’t currently enforced, but could be in the future.
depsHostHost
A list of dependencies whose host and target platforms match the new derivation’s host platform. In practice, this would usually be tools used by compilers for macros or a metaprogramming system, or libraries used by the macros or metaprogramming code itself. It’s always preferable to use a depsBuildBuild
dependency in the derivation being built over a depsHostHost
on the tool doing the building for this purpose.
buildInputs
A list of dependencies whose host platform and target platform match the new derivation’s. This would be called depsHostTarget
but for historical continuity. If the dependency doesn’t care about the target platform (i.e. isn’t a compiler or similar tool), put it here, rather than in depsBuildBuild
.
These are often programs and libraries used by the new derivation at run-time, but that isn’t always the case. For example, the machine code in a statically-linked library is only used at run-time, but the derivation containing the library is only needed at build-time. Even in the dynamic case, the library may also be needed at build-time to appease the linker.
depsTargetTarget
A list of dependencies whose host platform matches the new derivation’s target platform. These are packages that run on the target platform, e.g. the standard library or run-time deps of standard library that a compiler insists on knowing about. It’s poor form in almost all cases for a package to depend on another from a future stage [future stage corresponding to positive offset]. Do not use this attribute unless you are packaging a compiler and are sure it is needed.
depsBuildBuildPropagated
The propagated equivalent of depsBuildBuild
. This perhaps never ought to be used, but it is included for consistency [see below for the others].
propagatedNativeBuildInputs
The propagated equivalent of nativeBuildInputs
. This would be called depsBuildHostPropagated
but for historical continuity. For example, if package Y
has propagatedNativeBuildInputs = [X]
, and package Z
has buildInputs = [Y]
, then package Z
will be built as if it included package X
in its nativeBuildInputs
. If instead, package Z
has nativeBuildInputs = [Y]
, then Z
will be built as if it included X
in the depsBuildBuild
of package Z
, because of the sum of the two -1
host offsets.
depsBuildTargetPropagated
The propagated equivalent of depsBuildTarget
. This is prefixed for the same reason of alerting potential users.
depsHostHostPropagated
The propagated equivalent of depsHostHost
.
propagatedBuildInputs
The propagated equivalent of buildInputs
. This would be called depsHostTargetPropagated
but for historical continuity.
depsTargetTargetPropagated
The propagated equivalent of depsTargetTarget
. This is prefixed for the same reason of alerting potential users.
stdenv
initialisation NIX_DEBUG
A number between 0 and 7 indicating how much information to log. If set to 1 or higher, stdenv
will print moderate debugging information during the build. In particular, the gcc
and ld
wrapper scripts will print out the complete command line passed to the wrapped tools. If set to 6 or higher, the stdenv
setup script will be run with set -x
tracing. If set to 7 or higher, the gcc
and ld
wrapper scripts will also be run with set -x
tracing.
enableParallelBuilding
If set to true
, stdenv
will pass specific flags to make
and other build tools to enable parallel building with up to build-cores
workers.
Unless set to false
, some build systems with good support for parallel building including cmake
, meson
, and qmake
will set it to true
.
mkDerivation
If you pass a function to mkDerivation
, it will receive as its argument the final arguments, including the overrides when reinvoked via overrideAttrs
. For example:
mkDerivation (finalAttrs: {
pname = "hello";
withFeature = true;
configureFlags =
lib.optionals finalAttrs.withFeature ["--with-feature"];
})
Note that this does not use the rec
keyword to reuse withFeature
in configureFlags
.
The rec
keyword works at the syntax level and is unaware of overriding.
Instead, the definition references finalAttrs
, allowing users to change withFeature
consistently with overrideAttrs
.
finalAttrs
also contains the attribute finalPackage
, which includes the output paths, etc.
Let’s look at a more elaborate example to understand the differences between various bindings:
# `pkg` is the _original_ definition (for illustration purposes)
let pkg =
mkDerivation (finalAttrs: {
# ...
# An example attribute
packages = [];
# `passthru.tests` is a commonly defined attribute.
passthru.tests.simple = f finalAttrs.finalPackage;
# An example of an attribute containing a function
passthru.appendPackages = packages':
finalAttrs.finalPackage.overrideAttrs (newSelf: super: {
packages = super.packages ++ packages';
});
# For illustration purposes; referenced as
# `(pkg.overrideAttrs(x)).finalAttrs` etc in the text below.
passthru.finalAttrs = finalAttrs;
passthru.original = pkg;
});
in pkg
Unlike the pkg
binding in the above example, the finalAttrs
parameter always references the final attributes. For instance (pkg.overrideAttrs(x)).finalAttrs.finalPackage
is identical to pkg.overrideAttrs(x)
, whereas (pkg.overrideAttrs(x)).original
is the same as the original pkg
.
See also the section about passthru.tests
.
stdenv.mkDerivation
sets the Nix derivation’s builder to a script that loads the stdenv setup.sh
bash library and calls genericBuild
. Most packaging functions rely on this default builder.
This generic command either invokes a script at buildCommandPath, or a buildCommand, or a number of phases. Package builds are split into phases to make it easier to override specific parts of the build (e.g., unpacking the sources or installing the binaries).
Each phase can be overridden in its entirety either by setting the environment variable namePhase
to a string containing some shell commands to be executed, or by redefining the shell function namePhase
. The former is convenient to override a phase from the derivation, while the latter is convenient from a build script. However, typically one only wants to add some commands to a phase, e.g. by defining postInstall
or preFixup
, as skipping some of the default actions may have unexpected consequences. The default script for each phase is defined in the file pkgs/stdenv/generic/setup.sh
.
When overriding a phase, for example installPhase
, it is important to start with runHook preInstall
and end it with runHook postInstall
, otherwise preInstall
and postInstall
will not be run. Even if you don’t use them directly, it is good practice to do so anyways for downstream users who would want to add a postInstall
by overriding your derivation.
While inside an interactive nix-shell
, if you wanted to run all phases in the order they would be run in an actual build, you can invoke genericBuild
yourself.
There are a number of variables that control what phases are executed and in what order:
phases
Specifies the phases. You can change the order in which phases are executed, or add new phases, by setting this variable. If it’s not set, the default value is used, which is $prePhases unpackPhase patchPhase $preConfigurePhases configurePhase $preBuildPhases buildPhase checkPhase $preInstallPhases installPhase fixupPhase installCheckPhase $preDistPhases distPhase $postPhases
.
The elements of phases
must not contain spaces. If phases
is specified as a Nix Language attribute, it should be specified as lists instead of strings. The same rules apply to the *Phases
variables.
It is discouraged to set this variable, as it is easy to miss some important functionality hidden in some of the less obviously needed phases (like fixupPhase
which patches the shebang of scripts).
Usually, if you just want to add a few phases, it’s more convenient to set one of the *Phases
variables below.
prePhases
Additional phases executed before any of the default phases.
preConfigurePhases
Additional phases executed just before the configure phase.
preBuildPhases
Additional phases executed just before the build phase.
preInstallPhases
Additional phases executed just before the install phase.
preFixupPhases
Additional phases executed just before the fixup phase.
preDistPhases
Additional phases executed just before the distribution phase.
postPhases
Additional phases executed after any of the default phases.
The unpack phase is responsible for unpacking the source code of the package. The default implementation of unpackPhase
unpacks the source files listed in the src
environment variable to the current directory. It supports the following files by default:
These can optionally be compressed using gzip
(.tar.gz
, .tgz
or .tar.Z
), bzip2
(.tar.bz2
, .tbz2
or .tbz
) or xz
(.tar.xz
, .tar.lzma
or .txz
).
Zip files are unpacked using unzip
. However, unzip
is not in the standard environment, so you should add it to nativeBuildInputs
yourself.
These are copied to the current directory. The hash part of the file name is stripped, e.g. /nix/store/1wydxgby13cz...-my-sources
would be copied to my-sources
.
Additional file types can be supported by setting the unpackCmd
variable (see below).
srcs
/ src
The list of source files or directories to be unpacked or copied. One of these must be set. Note that if you use srcs
, you should also set sourceRoot
or setSourceRoot
.
sourceRoot
After unpacking all of src
and srcs
, if neither of sourceRoot
and setSourceRoot
are set, unpackPhase
of the generic builder checks that the unpacking produced a single directory and moves the current working directory into it.
If unpackPhase
produces multiple source directories, you should set sourceRoot
to the name of the intended directory.
You can also set sourceRoot = ".";
if you want to control it yourself in a later phase.
For example, if you want your build to start in a sub-directory inside your sources, and you are using fetchzip
-derived src
(like fetchFromGitHub
or similar), you need to set sourceRoot = "${src.name}/my-sub-directory"
.
setSourceRoot
Alternatively to setting sourceRoot
, you can set setSourceRoot
to a shell command to be evaluated by the unpack phase after the sources have been unpacked. This command must set sourceRoot
.
For example, if you are using fetchurl
on an archive file that gets unpacked into a single directory the name of which changes between package versions, and you want your build to start in its sub-directory, you need to set setSourceRoot = "sourceRoot=$(echo */my-sub-directory)";
, or in the case of multiple sources, you could use something more specific, like setSourceRoot = "sourceRoot=$(echo ${pname}-*/my-sub-directory)";
.
preUnpack
Hook executed at the start of the unpack phase.
postUnpack
Hook executed at the end of the unpack phase.
dontUnpack
Set to true to skip the unpack phase.
dontMakeSourcesWritable
If set to 1
, the unpacked sources are not made writable. By default, they are made writable to prevent problems with read-only sources. For example, copied store directories would be read-only without this.
unpackCmd
The unpack phase evaluates the string $unpackCmd
for any unrecognised file. The path to the current source file is contained in the curSrc
variable.
The patch phase applies the list of patches defined in the patches
variable.
dontPatch
Set to true to skip the patch phase.
patches
The list of patches. They must be in the format accepted by the patch
command, and may optionally be compressed using gzip
(.gz
), bzip2
(.bz2
) or xz
(.xz
).
patchFlags
Flags to be passed to patch
. If not set, the argument -p1
is used, which causes the leading directory component to be stripped from the file names in each patch.
prePatch
Hook executed at the start of the patch phase.
postPatch
Hook executed at the end of the patch phase.
The configure phase prepares the source tree for building. The default configurePhase
runs ./configure
(typically an Autoconf-generated script) if it exists.
configureScript
The name of the configure script. It defaults to ./configure
if it exists; otherwise, the configure phase is skipped. This can actually be a command (like perl ./Configure.pl
).
configureFlags
A list of strings passed as additional arguments to the configure script.
dontConfigure
Set to true to skip the configure phase.
configureFlagsArray
A shell array containing additional arguments passed to the configure script. You must use this instead of configureFlags
if the arguments contain spaces.
dontAddPrefix
By default, ./configure
is passed the concatenation of prefixKey
and prefix
on the command line. Disable this by setting dontAddPrefix
to true
.
prefix
The prefix under which the package must be installed, passed via the --prefix
option to the configure script. It defaults to $out
.
prefixKey
The key to use when specifying the installation prefix
. By default, this is set to --prefix=
as that is used by the majority of packages. Other packages may need --prefix
(with a trailing space) or PREFIX=
.
dontAddStaticConfigureFlags
By default, when building statically, stdenv will try to add build system appropriate configure flags to try to enable static builds.
If this is undesirable, set this variable to true.
dontAddDisableDepTrack
By default, the flag --disable-dependency-tracking
is added to the configure flags to speed up Automake-based builds. If this is undesirable, set this variable to true.
dontFixLibtool
By default, the configure phase applies some special hackery to all files called ltmain.sh
before running the configure script in order to improve the purity of Libtool-based packages [4] . If this is undesirable, set this variable to true.
dontDisableStatic
By default, when the configure script has --enable-static
, the option --disable-static
is added to the configure flags.
If this is undesirable, set this variable to true. It is automatically set to true when building statically, for example through pkgsStatic
.
configurePlatforms
By default, when cross compiling, the configure script has --build=...
and --host=...
passed. Packages can instead pass [ "build" "host" "target" ]
or a subset to control exactly which platform flags are passed. Compilers and other tools can use this to also pass the target platform. [5]
preConfigure
Hook executed at the start of the configure phase.
postConfigure
Hook executed at the end of the configure phase.
The build phase is responsible for actually building the package (e.g. compiling it). The default buildPhase
calls make
if a file named Makefile
, makefile
or GNUmakefile
exists in the current directory (or the makefile
is explicitly set); otherwise it does nothing.
dontBuild
Set to true to skip the build phase.
makefile
The file name of the Makefile.
makeFlags
A list of strings passed as additional flags to make
. These flags are also used by the default install and check phase. For setting make flags specific to the build phase, use buildFlags
(see below).
{
makeFlags = [ "PREFIX=$(out)" ];
}
The flags are quoted in bash, but environment variables can be specified by using the make syntax.
makeFlagsArray
A shell array containing additional arguments passed to make
. You must use this instead of makeFlags
if the arguments contain spaces, e.g.
{
preBuild = ''
makeFlagsArray+=(CFLAGS="-O0 -g" LDFLAGS="-lfoo -lbar")
'';
}
Note that shell arrays cannot be passed through environment variables, so you cannot set makeFlagsArray
in a derivation attribute (because those are passed through environment variables): you have to define them in shell code.
buildFlags
/ buildFlagsArray
A list of strings passed as additional flags to make
. Like makeFlags
and makeFlagsArray
, but only used by the build phase. Any build targets should be specified as part of the buildFlags
.
preBuild
Hook executed at the start of the build phase.
postBuild
Hook executed at the end of the build phase.
You can set flags for make
through the makeFlags
variable.
Before and after running make
, the hooks preBuild
and postBuild
are called, respectively.
The check phase checks whether the package was built correctly by running its test suite. The default checkPhase
calls make $checkTarget
, but only if the doCheck
variable is enabled.
It is highly recommended, for packages’ sources that are not distributed with any tests, to at least use versionCheckHook
to test that the resulting executable is basically functional.
doCheck
Controls whether the check phase is executed. By default it is skipped, but if doCheck
is set to true, the check phase is usually executed. Thus you should set
{
doCheck = true;
}
in the derivation to enable checks. The exception is cross compilation. Cross compiled builds never run tests, no matter how doCheck
is set, as the newly-built program won’t run on the platform used to build it.
makeFlags
/ makeFlagsArray
/ makefile
See the build phase for details.
checkTarget
The make
target that runs the tests.
If unset, use check
if it exists, otherwise test
; if neither is found, do nothing.
checkFlags
/ checkFlagsArray
A list of strings passed as additional flags to make
. Like makeFlags
and makeFlagsArray
, but only used by the check phase. Unlike with buildFlags
, the checkTarget
is automatically added to the make
invocation in addition to any checkFlags
specified.
checkInputs
A list of host dependencies used by the phase, usually libraries linked into executables built during tests. This gets included in buildInputs
when doCheck
is set.
nativeCheckInputs
A list of native dependencies used by the phase, notably tools needed on $PATH
. This gets included in nativeBuildInputs
when doCheck
is set.
preCheck
Hook executed at the start of the check phase.
postCheck
Hook executed at the end of the check phase.
The install phase is responsible for installing the package in the Nix store under out
. The default installPhase
creates the directory $out
and calls make install
.
dontInstall
Set to true to skip the install phase.
makeFlags
/ makeFlagsArray
/ makefile
See the build phase for details.
installTargets
The make targets that perform the installation. Defaults to install
. Example:
{
installTargets = "install-bin install-doc";
}
installFlags
/ installFlagsArray
A list of strings passed as additional flags to make
. Like makeFlags
and makeFlagsArray
, but only used by the install phase. Unlike with buildFlags
, the installTargets
are automatically added to the make
invocation in addition to any installFlags
specified.
preInstall
Hook executed at the start of the install phase.
postInstall
Hook executed at the end of the install phase.
The fixup phase performs (Nix-specific) post-processing actions on the files installed under $out
by the install phase. The default fixupPhase
does the following:
It moves the man/
, doc/
and info/
subdirectories of $out
to share/
.
It strips libraries and executables of debug information.
On Linux, it applies the patchelf
command to ELF executables and libraries to remove unused directories from the RPATH
in order to prevent unnecessary runtime dependencies.
It rewrites the interpreter paths of shell scripts to paths found in PATH
. E.g., /usr/bin/perl
will be rewritten to /nix/store/some-perl/bin/perl
found in PATH
. See the section called “patch-shebangs.sh
” for details.
dontFixup
Set to true to skip the fixup phase.
dontStrip
If set, libraries and executables are not stripped. By default, they are.
dontStripHost
Like dontStrip
, but only affects the strip
command targeting the package’s host platform. Useful when supporting cross compilation, but otherwise feel free to ignore.
dontStripTarget
Like dontStrip
, but only affects the strip
command targeting the packages’ target platform. Useful when supporting cross compilation, but otherwise feel free to ignore.
dontMoveSbin
If set, files in $out/sbin
are not moved to $out/bin
. By default, they are.
stripAllList
List of directories to search for libraries and executables from which all symbols should be stripped. By default, it’s empty. Stripping all symbols is risky, since it may remove not just debug symbols but also ELF information necessary for normal execution.
stripAllListTarget
Like stripAllList
, but only applies to packages’ target platform. By default, it’s empty. Useful when supporting cross compilation.
stripAllFlags
Flags passed to the strip
command applied to the files in the directories listed in stripAllList
. Defaults to -s
(i.e. --strip-all
).
stripDebugList
List of directories to search for libraries and executables from which only debugging-related symbols should be stripped. It defaults to lib lib32 lib64 libexec bin sbin
.
stripDebugListTarget
Like stripDebugList
, but only applies to packages’ target platform. By default, it’s empty. Useful when supporting cross compilation.
stripDebugFlags
Flags passed to the strip
command applied to the files in the directories listed in stripDebugList
. Defaults to -S
(i.e. --strip-debug
).
stripExclude
A list of filenames or path patterns to avoid stripping. A file is excluded if its name or path (from the derivation root) matches.
This example prevents all *.rlib
files from being stripped:
stdenv.mkDerivation {
# ...
stripExclude = [ "*.rlib" ];
}
This example prevents files within certain paths from being stripped:
stdenv.mkDerivation {
# ...
stripExclude = [ "lib/modules/*/build/*" ];
}
dontPatchELF
If set, the patchelf
command is not used to remove unnecessary RPATH
entries. Only applies to Linux.
dontPatchShebangs
If set, scripts starting with #!
do not have their interpreter paths rewritten to paths in the Nix store. See the section called “patch-shebangs.sh
” on how patching shebangs works.
dontPruneLibtoolFiles
If set, libtool .la
files associated with shared libraries won’t have their dependency_libs
field cleared.
forceShare
The list of directories that must be moved from $out
to $out/share
. Defaults to man doc info
.
setupHook
A package can export a setup hook by setting this variable. The setup hook, if defined, is copied to $out/nix-support/setup-hook
. Environment variables are then substituted in it using substituteAll
.
preFixup
Hook executed at the start of the fixup phase.
postFixup
Hook executed at the end of the fixup phase.
separateDebugInfo
If set to true
, the standard environment will enable debug information in C/C++ builds. After installation, the debug information will be separated from the executables and stored in the output named debug
. (This output is enabled automatically; you don’t need to set the outputs
attribute explicitly.) To be precise, the debug information is stored in debug/lib/debug/.build-id/XX/YYYY…
, where <XXYYYY…> is the <build ID> of the binary — a SHA-1 hash of the contents of the binary. Debuggers like GDB use the build ID to look up the separated debug information.
To make GDB find debug information for the socat
package and its dependencies, you can use the following shell.nix
:
let
pkgs = import ./. {
config = {};
overlays = [
(final: prev: {
ncurses = prev.ncurses.overrideAttrs { separateDebugInfo = true; };
readline = prev.readline.overrideAttrs { separateDebugInfo = true; };
})
];
};
myDebugInfoDirs = pkgs.symlinkJoin {
name = "myDebugInfoDirs";
paths = with pkgs; [
glibc.debug
ncurses.debug
openssl.debug
readline.debug
];
};
in
pkgs.mkShell {
NIX_DEBUG_INFO_DIRS = "${pkgs.lib.getLib myDebugInfoDirs}/lib/debug";
packages = [
pkgs.gdb
pkgs.socat
];
shellHook = ''
${pkgs.lib.getBin pkgs.gdb}/bin/gdb ${pkgs.lib.getBin pkgs.socat}/bin/socat
'';
}
This setup works as follows:
Add overlays
to the package set, since debug symbols are disabled for ncurses
and readline
by default.
Create a derivation to combine all required debug symbols under one path with symlinkJoin
.
Set the environment variable NIX_DEBUG_INFO_DIRS
in the shell. Nixpkgs patches gdb
to use it for looking up debug symbols.
Run gdb
on the socat
binary on shell startup in the shellHook
. Here we use lib.getBin
to ensure that the correct derivation output is selected rather than the default one.
The installCheck phase checks whether the package was installed correctly by running its test suite against the installed directories. The default installCheck
calls make installcheck
.
It is often better to add tests that are not part of the source distribution to passthru.tests
(see
the section called “passthru.tests
”). This avoids adding overhead to every build and enables us to run them independently.
doInstallCheck
Controls whether the installCheck phase is executed. By default it is skipped, but if doInstallCheck
is set to true, the installCheck phase is usually executed. Thus you should set
{
doInstallCheck = true;
}
in the derivation to enable install checks. The exception is cross compilation. Cross compiled builds never run tests, no matter how doInstallCheck
is set, as the newly-built program won’t run on the platform used to build it.
installCheckTarget
The make target that runs the install tests. Defaults to installcheck
.
installCheckFlags
/ installCheckFlagsArray
A list of strings passed as additional flags to make
. Like makeFlags
and makeFlagsArray
, but only used by the installCheck phase.
installCheckInputs
A list of host dependencies used by the phase, usually libraries linked into executables built during tests. This gets included in buildInputs
when doInstallCheck
is set.
nativeInstallCheckInputs
A list of native dependencies used by the phase, notably tools needed on $PATH
. This gets included in nativeBuildInputs
when doInstallCheck
is set.
preInstallCheck
Hook executed at the start of the installCheck phase.
postInstallCheck
Hook executed at the end of the installCheck phase.
The distribution phase is intended to produce a source distribution of the package. The default distPhase
first calls make dist
, then it copies the resulting source tarballs to $out/tarballs/
. This phase is only executed if the attribute doDist
is set.
doDist
If set, the distribution phase is executed.
distTarget
The make target that produces the distribution. Defaults to dist
.
distFlags
/ distFlagsArray
Additional flags passed to make
.
tarballs
The names of the source distribution files to be copied to $out/tarballs/
. It can contain shell wildcards. The default is *.tar.gz
.
dontCopyDist
If set, no files are copied to $out/tarballs/
.
preDist
Hook executed at the start of the distribution phase.
postDist
Hook executed at the end of the distribution phase.
makeWrapper
<executable> <wrapperfile> <args> remove-references-to -t
<storepath> [ -t
<storepath> … ] <file> … runHook
<hook> substitute
<infile> <outfile> <subs> substituteInPlace
<multiple files> <subs> substituteAll
<infile> <outfile> substituteAllInPlace
<file> stripHash
<path> wrapProgram
<executable> <makeWrapperArgs> prependToVar
<variableName> <elements…> appendToVar
<variableName> <elements…> The standard environment provides a number of useful functions.
makeWrapper
<executable> <wrapperfile> <args> Constructs a wrapper for a program with various possible arguments. It is defined as part of 2 setup-hooks named makeWrapper
and makeBinaryWrapper
that implement the same bash functions. Hence, to use it you have to add makeWrapper
to your nativeBuildInputs
. Here’s an example usage:
# adds `FOOBAR=baz` to `$out/bin/foo`’s environment
makeWrapper $out/bin/foo $wrapperfile --set FOOBAR baz
# Prefixes the binary paths of `hello` and `git`
# and suffixes the binary path of `xdg-utils`.
# Be advised that paths often should be patched in directly
# (via string replacements or in `configurePhase`).
makeWrapper $out/bin/foo $wrapperfile \
--prefix PATH : ${lib.makeBinPath [ hello git ]} \
--suffix PATH : ${lib.makeBinPath [ xdg-utils ]}
Packages may expect or require other utilities to be available at runtime.
makeWrapper
can be used to add packages to a PATH
environment variable local to a wrapper.
Use --prefix
to explicitly set dependencies in PATH
.
--prefix
essentially hard-codes dependencies into the wrapper.
They cannot be overridden without rebuilding the package.
If dependencies should be resolved at runtime, use --suffix
to append fallback values to PATH
.
There’s many more kinds of arguments, they are documented in nixpkgs/pkgs/build-support/setup-hooks/make-wrapper.sh
for the makeWrapper
implementation and in nixpkgs/pkgs/build-support/setup-hooks/make-binary-wrapper/make-binary-wrapper.sh
for the makeBinaryWrapper
implementation.
wrapProgram
is a convenience function you probably want to use most of the time, implemented by both makeWrapper
and makeBinaryWrapper
.
Using the makeBinaryWrapper
implementation is usually preferred, as it creates a tiny compiled wrapper executable, that can be used as a shebang interpreter. This is needed mostly on Darwin, where shebangs cannot point to scripts, due to a limitation with the execve
-syscall. Compiled wrappers generated by makeBinaryWrapper
can be inspected with less <path-to-wrapper>
- by scrolling past the binary data you should be able to see the shell command that generated the executable and there see the environment variables that were injected into the wrapper.
remove-references-to -t
<storepath> [ -t
<storepath> … ] <file> … Removes the references of the specified files to the specified store files. This is done without changing the size of the file by replacing the hash by eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee
, and should work on compiled executables. This is meant to be used to remove the dependency of the output on inputs that are known to be unnecessary at runtime. Of course, reckless usage will break the patched programs.
To use this, add removeReferencesTo
to nativeBuildInputs
.
As remove-references-to
is an actual executable and not a shell function, it can be used with find
.
Example removing all references to the compiler in the output:
{
postInstall = ''
find "$out" -type f -exec remove-references-to -t ${stdenv.cc} '{}' +
'';
}
runHook
<hook> Execute <hook> and the values in the array associated with it. The array’s name is determined by removing Hook
from the end of <hook> and appending Hooks
.
For example, runHook postHook
would run the hook postHook
and all of the values contained in the postHooks
array, if it exists.
substitute
<infile> <outfile> <subs> Performs string substitution on the contents of <infile>, writing the result to <outfile>. The substitutions in <subs> are of the following form:
--replace-fail
<s1> <s2> Replace every occurrence of the string <s1> by <s2>. Will error if no change is made.
--replace-warn
<s1> <s2> Replace every occurrence of the string <s1> by <s2>. Will print a warning if no change is made.
--replace-quiet
<s1> <s2> Replace every occurrence of the string <s1> by <s2>. Will do nothing if no change can be made.
--subst-var
<varName> Replace every occurrence of @varName@
by the contents of the environment variable <varName>. This is useful for generating files from templates, using @...@
in the template as placeholders.
--subst-var-by
<varName> <s> Replace every occurrence of @varName@
by the string <s>.
Example:
substitute ./foo.in ./foo.out \
--replace-fail /usr/bin/bar $bar/bin/bar \
--replace-fail "a string containing spaces" "some other text" \
--subst-var someVar
substituteInPlace
<multiple files> <subs> Like substitute
, but performs the substitutions in place on the files passed.
substituteAll
<infile> <outfile> Replaces every occurrence of @varName@
, where <varName> is any environment variable, in <infile>, writing the result to <outfile>. For instance, if <infile> has the contents
#! @bash@/bin/sh
PATH=@coreutils@/bin
echo @foo@
and the environment contains bash=/nix/store/bmwp0q28cf21...-bash-3.2-p39
and coreutils=/nix/store/68afga4khv0w...-coreutils-6.12
, but does not contain the variable foo
, then the output will be
#! /nix/store/bmwp0q28cf21...-bash-3.2-p39/bin/sh
PATH=/nix/store/68afga4khv0w...-coreutils-6.12/bin
echo @foo@
That is, no substitution is performed for undefined variables.
Environment variables that start with an uppercase letter or an underscore are filtered out, to prevent global variables (like HOME
) or private variables (like __ETC_PROFILE_DONE
) from accidentally getting substituted. The variables also have to be valid bash “names”, as defined in the bash manpage (alphanumeric or _
, must not start with a number).
substituteAllInPlace
<file> Like substituteAll
, but performs the substitutions in place on the file <file>.
stripHash
<path> Strips the directory and hash part of a store path, outputting the name part to stdout
. For example:
# prints coreutils-8.24
stripHash "/nix/store/9s9r019176g7cvn2nvcw41gsp862y6b4-coreutils-8.24"
If you wish to store the result in another variable, then the following idiom may be useful:
name="/nix/store/9s9r019176g7cvn2nvcw41gsp862y6b4-coreutils-8.24"
someVar=$(stripHash $name)
wrapProgram
<executable> <makeWrapperArgs> Convenience function for makeWrapper
that replaces <executable>
with a wrapper that executes the original program. It takes all the same arguments as makeWrapper
, except for --inherit-argv0
(used by the makeBinaryWrapper
implementation) and --argv0
(used by both makeWrapper
and makeBinaryWrapper
wrapper implementations).
If you will apply it multiple times, it will overwrite the wrapper file and you will end up with double wrapping, which should be avoided.
prependToVar
<variableName> <elements…> Prepend elements to a variable.
Example:
$ configureFlags="--disable-static"
$ prependToVar configureFlags --disable-dependency-tracking --enable-foo
$ echo $configureFlags
--disable-dependency-tracking --enable-foo --disable-static
appendToVar
<variableName> <elements…> Append elements to a variable.
Example:
$ configureFlags="--disable-static"
$ appendToVar configureFlags --disable-dependency-tracking --enable-foo
$ echo $configureFlags
--disable-static --disable-dependency-tracking --enable-foo
Nix itself considers a build-time dependency as merely something that should previously be built and accessible at build time—packages themselves are on their own to perform any additional setup. In most cases, that is fine, and the downstream derivation can deal with its own dependencies. But for a few common tasks, that would result in almost every package doing the same sort of setup work—depending not on the package itself, but entirely on which dependencies were used.
In order to alleviate this burden, the setup hook mechanism was written, where any package can include a shell script that [by convention rather than enforcement by Nix], any downstream reverse-dependency will source as part of its build process. That allows the downstream dependency to merely specify its dependencies, and lets those dependencies effectively initialize themselves. No boilerplate mirroring the list of dependencies is needed.
The setup hook mechanism is a bit of a sledgehammer though: a powerful feature with a broad and indiscriminate area of effect. The combination of its power and implicit use may be expedient, but isn’t without costs. Nix itself is unchanged, but the spirit of added dependencies being effect-free is violated even if the latter isn’t. For example, if a derivation path is mentioned more than once, Nix itself doesn’t care and makes sure the dependency derivation is already built just the same—depending is just needing something to exist, and needing is idempotent. However, a dependency specified twice will have its setup hook run twice, and that could easily change the build environment (though a well-written setup hook will therefore strive to be idempotent so this is in fact not observable). More broadly, setup hooks are anti-modular in that multiple dependencies, whether the same or different, should not interfere and yet their setup hooks may well do so.
The most typical use of the setup hook is actually to add other hooks which are then run (i.e. after all the setup hooks) on each dependency. For example, the C compiler wrapper’s setup hook feeds itself flags for each dependency that contains relevant libraries and headers. This is done by defining a bash function, and appending its name to one of envBuildBuildHooks
, envBuildHostHooks
, envBuildTargetHooks
, envHostHostHooks
, envHostTargetHooks
, or envTargetTargetHooks
. These 6 bash variables correspond to the 6 sorts of dependencies by platform (there’s 12 total but we ignore the propagated/non-propagated axis).
Packages adding a hook should not hard code a specific hook, but rather choose a variable relative to how they are included. Returning to the C compiler wrapper example, if the wrapper itself is an n
dependency, then it only wants to accumulate flags from n + 1
dependencies, as only those ones match the compiler’s target platform. The hostOffset
variable is defined with the current dependency’s host offset targetOffset
with its target offset, before its setup hook is sourced. Additionally, since most environment hooks don’t care about the target platform, that means the setup hook can append to the right bash array by doing something like
addEnvHooks "$hostOffset" myBashFunction
The existence of setups hooks has long been documented and packages inside Nixpkgs are free to use this mechanism. Other packages, however, should not rely on these mechanisms not changing between Nixpkgs versions. Because of the existing issues with this system, there’s little benefit from mandating it be stable for any period of time.
First, let’s cover some setup hooks that are part of Nixpkgs default stdenv
. This means that they are run for every package built using stdenv.mkDerivation
or when using a custom builder that has source $stdenv/setup
. Some of these are platform specific, so they may run on Linux but not Darwin or vice-versa.
move-docs.sh
This setup hook moves any installed documentation to the /share
subdirectory directory. This includes the man, doc and info directories. This is needed for legacy programs that do not know how to use the share
subdirectory.
compress-man-pages.sh
This setup hook compresses any man pages that have been installed. The compression is done using the gzip program. This helps to reduce the installed size of packages.
strip.sh
This runs the strip command on installed binaries and libraries. This removes unnecessary information like debug symbols when they are not needed. This also helps to reduce the installed size of packages.
patch-shebangs.sh
This setup hook patches installed scripts to add Nix store paths to their shebang interpreter as found in the build environment. The shebang line tells a Unix-like operating system which interpreter to use to execute the script’s contents.
The generic builder populates PATH
from inputs of the derivation.
Multiple paths can be specified.
patchShebangs [--build | --host] PATH...
--build
Look up commands available at build time
--host
Look up commands available at run time
patchShebangs --host /nix/store/<hash>-hello-1.0/bin
patchShebangs --build configure
#!/bin/sh
will be rewritten to #!/nix/store/<hash>-some-bash/bin/sh
.
#!/usr/bin/env
gets special treatment: #!/usr/bin/env python
is rewritten to /nix/store/<hash>/bin/python
.
Interpreter paths that point to a valid Nix store location are not changed.
A script file must be marked as executable, otherwise it will not be considered.
This mechanism ensures that the interpreter for a given script is always found and is exactly the one specified by the build.
It can be disabled by setting dontPatchShebangs
:
stdenv.mkDerivation {
# ...
dontPatchShebangs = true;
# ...
}
The file patch-shebangs.sh
defines the patchShebangs
function. It is used to implement patchShebangsAuto
, the setup hook that is registered to run during the fixup phase by default.
If you need to run patchShebangs
at build time, it must be called explicitly within one of the build phases.
audit-tmpdir.sh
This verifies that no references are left from the install binaries to the directory used to build those binaries. This ensures that the binaries do not need things outside the Nix store. This is currently supported in Linux only.
multiple-outputs.sh
This setup hook adds configure flags that tell packages to install files into any one of the proper outputs listed in outputs
. This behavior can be turned off by setting setOutputFlags
to false in the derivation environment. See Multiple-output packages for more information.
move-sbin.sh
This setup hook moves any binaries installed in the sbin/
subdirectory into bin/
. In addition, a link is provided from sbin/
to bin/
for compatibility.
move-lib64.sh
This setup hook moves any libraries installed in the lib64/
subdirectory into lib/
. In addition, a link is provided from lib64/
to lib/
for compatibility.
move-systemd-user-units.sh
This setup hook moves any systemd user units installed in the lib/
subdirectory into share/
. In addition, a link is provided from share/
to lib/
for compatibility. This is needed for systemd to find user services when installed into the user profile.
This hook only runs when compiling for Linux.
set-source-date-epoch-to-latest.sh
This sets SOURCE_DATE_EPOCH
to the modification time of the most recent file.
The Bintools Wrapper wraps the binary utilities for a bunch of miscellaneous purposes. These are GNU Binutils when targeting Linux, and a mix of cctools and GNU binutils for Darwin. [The “Bintools” name is supposed to be a compromise between “Binutils” and “cctools” not denoting any specific implementation.] Specifically, the underlying bintools package, and a C standard library (glibc or Darwin’s libSystem, just for the dynamic loader) are all fed in, and dependency finding, hardening (see below), and purity checks for each are handled by the Bintools Wrapper. Packages typically depend on CC Wrapper, which in turn (at run time) depends on the Bintools Wrapper.
The Bintools Wrapper was only just recently split off from CC Wrapper, so the division of labor is still being worked out. For example, it shouldn’t care about the C standard library, but just take a derivation with the dynamic loader (which happens to be the glibc on linux). Dependency finding however is a task both wrappers will continue to need to share, and probably the most important to understand. It is currently accomplished by collecting directories of host-platform dependencies (i.e. buildInputs
and nativeBuildInputs
) in environment variables. The Bintools Wrapper’s setup hook causes any lib
and lib64
subdirectories to be added to NIX_LDFLAGS
. Since the CC Wrapper and the Bintools Wrapper use the same strategy, most of the Bintools Wrapper code is sparsely commented and refers to the CC Wrapper. But the CC Wrapper’s code, by contrast, has quite lengthy comments. The Bintools Wrapper merely cites those, rather than repeating them, to avoid falling out of sync.
A final task of the setup hook is defining a number of standard environment variables to tell build systems which executables fulfill which purpose. They are defined to just be the base name of the tools, under the assumption that the Bintools Wrapper’s binaries will be on the path. Firstly, this helps poorly-written packages, e.g. ones that look for just gcc
when CC
isn’t defined yet clang
is to be used. Secondly, this helps packages not get confused when cross-compiling, in which case multiple Bintools Wrappers may simultaneously be in use. [6] BUILD_
- and TARGET_
-prefixed versions of the normal environment variable are defined for additional Bintools Wrappers, properly disambiguating them.
A problem with this final task is that the Bintools Wrapper is honest and defines LD
as ld
. Most packages, however, firstly use the C compiler for linking, secondly use LD
anyways, defining it as the C compiler, and thirdly, only so define LD
when it is undefined as a fallback. This triple-threat means Bintools Wrapper will break those packages, as LD is already defined as the actual linker which the package won’t override yet doesn’t want to use. The workaround is to define, just for the problematic package, LD
as the C compiler. A good way to do this would be preConfigure = "LD=$CC"
.
The CC Wrapper wraps a C toolchain for a bunch of miscellaneous purposes. Specifically, a C compiler (GCC or Clang), wrapped binary tools, and a C standard library (glibc or Darwin’s libSystem, just for the dynamic loader) are all fed in, and dependency finding, hardening (see below), and purity checks for each are handled by the CC Wrapper. Packages typically depend on the CC Wrapper, which in turn (at run-time) depends on the Bintools Wrapper.
Dependency finding is undoubtedly the main task of the CC Wrapper. This works just like the Bintools Wrapper, except that any include
subdirectory of any relevant dependency is added to NIX_CFLAGS_COMPILE
. The setup hook itself contains elaborate comments describing the exact mechanism by which this is accomplished.
Similarly, the CC Wrapper follows the Bintools Wrapper in defining standard environment variables with the names of the tools it wraps, for the same reasons described above. Importantly, while it includes a cc
symlink to the c compiler for portability, the CC
will be defined using the compiler’s “real name” (i.e. gcc
or clang
). This helps lousy build systems that inspect on the name of the compiler rather than run it.
Here are some more packages that provide a setup hook. Since the list of hooks is extensible, this is not an exhaustive list. The mechanism is only to be used as a last resort, so it might cover most uses.
Many other packages provide hooks, that are not part of stdenv
. You can find
these in the Hooks Reference.
If the file ${cc}/nix-support/cc-wrapper-hook
exists, it will be run at the end of the compiler wrapper.
If the file ${binutils}/nix-support/post-link-hook
exists, it will be run at the end of the linker wrapper.
These hooks allow a user to inject code into the wrappers.
As an example, these hooks can be used to extract extraBefore
, params
and extraAfter
which store all the command line arguments passed to the compiler and linker respectively.
Measures taken to prevent dependencies on packages outside the store, and what you can do to prevent them.
GCC doesn’t search in locations such as /usr/include
. In fact, attempts to add such directories through the -I
flag are filtered out. Likewise, the linker (from GNU binutils) doesn’t search in standard locations such as /usr/lib
. Programs built on Linux are linked against a GNU C Library that likewise doesn’t search in the default system locations.
There are flags available to harden packages at compile or link-time. These can be toggled using the stdenv.mkDerivation
parameters hardeningDisable
and hardeningEnable
.
Both parameters take a list of flags as strings. The special "all"
flag can be passed to hardeningDisable
to turn off all hardening. These flags can also be used as environment variables for testing or development purposes.
For more in-depth information on these hardening flags and hardening in general, refer to the Debian Wiki, Ubuntu Wiki, Gentoo Wiki, and the Arch Wiki.
Note that support for some hardening flags varies by compiler, CPU architecture, target OS and libc. Combinations of these that don’t support a particular hardening flag will silently ignore attempts to enable it. To see exactly which hardening flags are being employed in any invocation, the NIX_DEBUG
environment variable can be used.
The following flags are enabled by default and might require disabling with hardeningDisable
if the program to package is incompatible.
format
Adds the -Wformat -Wformat-security -Werror=format-security
compiler options. At present, this warns about calls to printf
and scanf
functions where the format string is not a string literal and there are no format arguments, as in printf(foo);
. This may be a security hole if the format string came from untrusted input and contains %n
.
This needs to be turned off or fixed for errors similar to:
/tmp/nix-build-zynaddsubfx-2.5.2.drv-0/zynaddsubfx-2.5.2/src/UI/guimain.cpp:571:28: error: format not a string literal and no format arguments [-Werror=format-security]
printf(help_message);
^
cc1plus: some warnings being treated as errors
stackprotector
Adds the -fstack-protector-strong --param ssp-buffer-size=4
compiler options. This adds safety checks against stack overwrites rendering many potential code injection attacks into aborting situations. In the best case this turns code injection vulnerabilities into denial of service or into non-issues (depending on the application).
This needs to be turned off or fixed for errors similar to:
bin/blib.a(bios_console.o): In function `bios_handle_cup':
/tmp/nix-build-ipxe-20141124-5cbdc41.drv-0/ipxe-5cbdc41/src/arch/i386/firmware/pcbios/bios_console.c:86: undefined reference to `__stack_chk_fail'
fortify
Adds the -O2 -D_FORTIFY_SOURCE=2
compiler options. During code generation the compiler knows a great deal of information about buffer sizes (where possible), and attempts to replace insecure unlimited length buffer function calls with length-limited ones. This is especially useful for old, crufty code. Additionally, format strings in writable memory that contain %n
are blocked. If an application depends on such a format string, it will need to be worked around.
Additionally, some warnings are enabled which might trigger build failures if compiler warnings are treated as errors in the package build. In this case, set env.NIX_CFLAGS_COMPILE
to -Wno-error=warning-type
.
This needs to be turned off or fixed for errors similar to:
malloc.c:404:15: error: return type is an incomplete type
malloc.c:410:19: error: storage size of 'ms' isn't known
strdup.h:22:1: error: expected identifier or '(' before '__extension__'
strsep.c:65:23: error: register name not specified for 'delim'
installwatch.c:3751:5: error: conflicting types for '__open_2'
fcntl2.h:50:4: error: call to '__open_missing_mode' declared with attribute error: open with O_CREAT or O_TMPFILE in second argument needs 3 arguments
Disabling fortify
implies disablement of fortify3
fortify3
Adds the -O2 -D_FORTIFY_SOURCE=3
compiler options. This expands the cases that can be protected by fortify-checks to include some situations with dynamic-length buffers whose length can be inferred at runtime using compiler hints.
Enabling this flag implies enablement of fortify
. Disabling this flag does not imply disablement of fortify
.
This flag can sometimes conflict with a build-system’s own attempts at enabling fortify support and result in errors complaining about redefinition of _FORTIFY_SOURCE
.
pic
Adds the -fPIC
compiler options. This options adds support for position independent code in shared libraries and thus making ASLR possible.
Most notably, the Linux kernel, kernel modules and other code not running in an operating system environment like boot loaders won’t build with PIC enabled. The compiler will is most cases complain that PIC is not supported for a specific build.
This needs to be turned off or fixed for assembler errors similar to:
ccbLfRgg.s: Assembler messages:
ccbLfRgg.s:33: Error: missing or invalid displacement expression `private_key_len@GOTOFF'
strictoverflow
Signed integer overflow is undefined behaviour according to the C standard. If it happens, it is an error in the program as it should check for overflow before it can happen, not afterwards. GCC provides built-in functions to perform arithmetic with overflow checking, which are correct and faster than any custom implementation. As a workaround, the option -fno-strict-overflow
makes gcc behave as if signed integer overflows were defined.
This flag should not trigger any build or runtime errors.
relro
Adds the -z relro
linker option. During program load, several ELF memory sections need to be written to by the linker, but can be turned read-only before turning over control to the program. This prevents some GOT (and .dtors) overwrite attacks, but at least the part of the GOT used by the dynamic linker (.got.plt) is still vulnerable.
This flag can break dynamic shared object loading. For instance, the module systems of Xorg and OpenCV are incompatible with this flag. In almost all cases the bindnow
flag must also be disabled and incompatible programs typically fail with similar errors at runtime.
bindnow
Adds the -z now
linker option. During program load, all dynamic symbols are resolved, allowing for the complete GOT to be marked read-only (due to relro
). This prevents GOT overwrite attacks. For very large applications, this can incur some performance loss during initial load while symbols are resolved, but this shouldn’t be an issue for daemons.
This flag can break dynamic shared object loading. For instance, the module systems of Xorg and PHP are incompatible with this flag. Programs incompatible with this flag often fail at runtime due to missing symbols, like:
intel_drv.so: undefined symbol: vgaHWFreeHWRec
zerocallusedregs
Adds the -fzero-call-used-regs=used-gpr
compiler option. This causes the general-purpose registers that an architecture’s calling convention considers “call-used” to be zeroed on return from the function. This can make it harder for attackers to construct useful ROP gadgets and also reduces the chance of data leakage from a function call.
The following flags are disabled by default and should be enabled with hardeningEnable
for packages that take untrusted input like network services.
pie
This flag is disabled by default for normal glibc
based NixOS package builds, but enabled by default for
musl
-based package builds, except on Aarch64 and Aarch32, where there are issues.
Statically-linked for OpenBSD builds, where it appears to be required to get a working binary.
Adds the -fPIE
compiler and -pie
linker options. Position Independent Executables are needed to take advantage of Address Space Layout Randomization, supported by modern kernel versions. While ASLR can already be enforced for data areas in the stack and heap (brk and mmap), the code areas must be compiled as position-independent. Shared libraries already do this with the pic
flag, so they gain ASLR automatically, but binary .text regions need to be build with pie
to gain ASLR. When this happens, ROP attacks are much harder since there are no static locations to bounce off of during a memory corruption attack.
Static libraries need to be compiled with -fPIE
so that executables can link them in with the -pie
linker option.
If the libraries lack -fPIE
, you will get the error recompile with -fPIE
.
shadowstack
Adds the -fcf-protection=return
compiler option. This enables the Shadow Stack feature supported by some newer processors, which maintains a user-inaccessible copy of the program’s stack containing only return-addresses. When returning from a function, the processor compares the return-address value on the two stacks and throws an error if they do not match, considering it a sign of corruption and possible tampering. This should significantly increase the difficulty of ROP attacks.
For the Shadow Stack to be enabled at runtime, all code linked into a process must be built with Shadow Stack enabled, so this is probably only useful to enable on a wide scale, so that all of a packages dependencies also have the feature enabled.
This is currently only supported on some newer Intel and AMD processors as part of the Intel CET set of features. However, the generated code should continue to work on older processors which will simply omit any of this checking.
This breaks some code that does advanced stack management or exception handling. If enabling this hardening flag it is important to test the result on a system that has known working and enabled CET support, so that any such breakage can be discovered.
trivialautovarinit
Adds the -ftrivial-auto-var-init=pattern
compiler option. This causes “trivially-initializable” uninitialized stack variables to be forcibly initialized with a nonzero value that is likely to cause a crash (and therefore be noticed). Uninitialized variables generally take on their values based on fragments of previous program state, and attackers can carefully manipulate that state to craft malicious initial values for these variables.
Use of this flag is controversial as it can prevent tools that detect uninitialized variable use (such as valgrind) from operating correctly.
This should be turned off or fixed for build errors such as:
sorry, unimplemented: __builtin_clear_padding not supported for variable length aggregates
stackclashprotection
This flag adds the -fstack-clash-protection
compiler option, which causes growth of a program’s stack to access each successive page in order. This should force the guard page to be accessed and cause an attempt to “jump over” this guard page to crash.
pacret
This flag adds the -mbranch-protection=pac-ret
compiler option on aarch64-linux targets. This uses ARM v8.3’s Pointer Authentication feature to sign function return pointers before adding them to the stack. The pointer’s authenticity is then validated before returning to its destination. This dramatically increases the difficulty of ROP exploitation techniques.
This may cause problems with code that does advanced stack manipulation, and debugging/stack-unwinding tools need to be pac-ret aware to work correctly when these features are in operation.
Pre-ARM v8.3 processors will ignore Pointer Authentication instructions, so code built with this flag will continue to work on older processors, though without any of the intended protections. If enabling this flag, it is recommended to ensure the resultant packages are tested against an ARM v8.3+ linux system with known-working Pointer Authentication support so that any breakage caused by this feature is actually detected.
The build platform is ignored because it is a mere implementation detail of the package satisfying the dependency: As a general programming principle, dependencies are always specified as interfaces, not concrete implementation.[1]
Currently, this means for native builds all dependencies are put on the PATH
. But in the future that may not be the case for sake of matching cross: the platforms would be assumed to be unique for native and cross builds alike, so only the depsBuild*
and nativeBuildInputs
would be added to the PATH
.[2]
The findInputs
function, currently residing in pkgs/stdenv/generic/setup.sh
, implements the propagation logic.[3]
It clears the sys_lib_*search_path
variables in the Libtool script to prevent Libtool from using libraries in /usr/lib
and such.[4]
Eventually these will be passed building natively as well, to improve determinism: build-time guessing, as is done today, is a risk of impurity.[5]
Each wrapper targets a single platform, so if binaries for multiple platforms are needed, the underlying binaries must be wrapped multiple times. As this is a property of the wrapper itself, the multiple wrappings are needed whether or not the same underlying binaries can target multiple platforms.[6]
Table of Contents
Nix packages can declare meta-attributes that contain information about a package such as a description, its homepage, its license, and so on. For instance, the GNU Hello package has a meta
declaration like this:
{
meta = {
description = "Program that produces a familiar, friendly greeting";
longDescription = ''
GNU Hello is a program that prints "Hello, world!" when you run it.
It is fully customizable.
'';
homepage = "https://www.gnu.org/software/hello/manual/";
license = lib.licenses.gpl3Plus;
maintainers = with lib.maintainers; [ eelco ];
platforms = lib.platforms.all;
};
}
Meta-attributes are not passed to the builder of the package. Thus, a change to a meta-attribute doesn’t trigger a recompilation of the package.
If the package is to be submitted to Nixpkgs, please check out the requirements for meta attributes in the contributing documentation.
It is expected that each meta-attribute is one of the following:
description
A short (one-line) description of the package. This is displayed on search.nixos.org.
The general requirements of a description are:
Be short, just one sentence.
Be capitalized.
Not start with definite (“The”) or indefinite (“A”/“An”) article.
Not start with the package name.
More generally, it should not refer to the package name.
Not end with a period (or any punctuation for that matter).
Provide factual information.
Avoid subjective language.
Wrong: "libpng is a library that allows you to decode PNG images."
Right: "Library for decoding PNG images"
longDescription
An arbitrarily long description of the package in CommonMark Markdown.
branch
Release branch. Used to specify that a package is not going to receive updates that are not in this branch; for example, Linux kernel 3.0 is supposed to be updated to 3.0.X, not 3.1.
homepage
The package’s homepage. Example: https://www.gnu.org/software/hello/manual/
downloadPage
The page where a link to the current version can be found. Example: https://ftp.gnu.org/gnu/hello/
changelog
A link or a list of links to the location of Changelog for a package. A link may use expansion to refer to the correct changelog version. Example: "https://git.savannah.gnu.org/cgit/hello.git/plain/NEWS?h=v${version}"
license
The license, or licenses, for the package. One from the attribute set defined in nixpkgs/lib/licenses.nix
. At this moment using both a list of licenses and a single license is valid. If the license field is in the form of a list representation, then it means that parts of the package are licensed differently. Each license should preferably be referenced by their attribute. The non-list attribute value can also be a space delimited string representation of the contained attribute shortNames
or spdxIds
. The following are all valid examples:
Single license referenced by attribute (preferred) lib.licenses.gpl3Only
.
Single license referenced by its attribute shortName (frowned upon) "gpl3Only"
.
Single license referenced by its attribute spdxId (frowned upon) "GPL-3.0-only"
.
Multiple licenses referenced by attribute (preferred) with lib.licenses; [ asl20 free ofl ]
.
Multiple licenses referenced as a space delimited string of attribute shortNames (frowned upon) "asl20 free ofl"
.
For details, see Licenses.
sourceProvenance
A list containing the type or types of source inputs from which the package is built, e.g. original source code, pre-built binaries, etc.
For details, see Source provenance.
maintainers
A list of the maintainers of this Nix expression. Maintainers are defined in nixpkgs/maintainers/maintainer-list.nix
. There is no restriction to becoming a maintainer, just add yourself to that list in a separate commit titled “maintainers: add alice” in the same pull request, and reference maintainers with maintainers = with lib.maintainers; [ alice bob ]
.
mainProgram
The name of the main binary for the package. This affects the binary nix run
executes. Example: "rg"
priority
The priority of the package, used by nix-env
to resolve file name conflicts between packages. See the manual page for nix-env
for details. Example: "10"
(a low-priority package).
platforms
The list of Nix platform types on which the package is supported. Hydra builds packages according to the platform specified. If no platform is specified, the package does not have prebuilt binaries. An example is:
{
meta.platforms = lib.platforms.linux;
}
Attribute Set lib.platforms
defines various common lists of platforms types.
badPlatforms
The list of Nix platform types on which the package is known not to be buildable.
Hydra will never create prebuilt binaries for these platform types, even if they are in meta.platforms
.
In general it is preferable to set meta.platforms = lib.platforms.all
and then exclude any platforms on which the package is known not to build.
For example, a package which requires dynamic linking and cannot be linked statically could use this:
{
meta.platforms = lib.platforms.all;
meta.badPlatforms = [ lib.systems.inspect.platformPatterns.isStatic ];
}
The lib.meta.availableOn
function can be used to test whether or not a package is available (i.e. buildable) on a given platform.
Some packages use this to automatically detect the maximum set of features with which they can be built.
For example, systemd
requires dynamic linking, and has a meta.badPlatforms
setting similar to the one above.
Packages which can be built with or without systemd
support will use lib.meta.availableOn
to detect whether or not systemd
is available on the hostPlatform
for which they are being built; if it is not available (e.g. due to a statically-linked host platform like pkgsStatic
) this support will be disabled by default.
timeout
A timeout (in seconds) for building the derivation. If the derivation takes longer than this time to build, Hydra will fail it due to breaking the timeout. However, all computers do not have the same computing power, hence some builders may decide to apply a multiplicative factor to this value. When filling this value in, try to keep it approximately consistent with other values already present in nixpkgs
.
meta
attributes are not stored in the instantiated derivation.
Therefore, this setting may be lost when the package is used as a dependency.
To be effective, it must be presented directly to an evaluation process that handles the meta.timeout
attribute.
hydraPlatforms
The list of Nix platform types for which the Hydra instance at hydra.nixos.org
will build the package. (Hydra is the Nix-based continuous build system.) It defaults to the value of meta.platforms
. Thus, the only reason to set meta.hydraPlatforms
is if you want hydra.nixos.org
to build the package on a subset of meta.platforms
, or not at all, e.g.
{
meta.platforms = lib.platforms.linux;
meta.hydraPlatforms = [];
}
broken
If set to true
, the package is marked as “broken”, meaning that it won’t show up in search.nixos.org, and cannot be built or installed unless the environment variable NIXPKGS_ALLOW_BROKEN
is set.
Such unconditionally-broken packages should be removed from Nixpkgs eventually unless they are fixed.
The value of this attribute can depend on a package’s arguments, including stdenv
.
This means that broken
can be used to express constraints, for example:
Does not cross compile
{
meta.broken = !(stdenv.buildPlatform.canExecute stdenv.hostPlatform);
}
Broken if all of a certain set of its dependencies are broken
{
meta.broken = lib.all (map (p: p.meta.broken) [ glibc musl ]);
}
This makes broken
strictly more powerful than meta.badPlatforms
.
However meta.availableOn
currently examines only meta.platforms
and meta.badPlatforms
, so meta.broken
does not influence the default values for optional dependencies.
The meta.license
attribute should preferably contain a value from lib.licenses
defined in nixpkgs/lib/licenses.nix
, or in-place license description of the same format if the license is unlikely to be useful in another expression.
Although it’s typically better to indicate the specific license, a few generic options are available:
lib.licenses.free
, "free"
Catch-all for free software licenses not listed above.
lib.licenses.unfreeRedistributable
, "unfree-redistributable"
Unfree package that can be redistributed in binary form. That is, it’s legal to redistribute the output of the derivation. This means that the package can be included in the Nixpkgs channel.
Sometimes proprietary software can only be redistributed unmodified. Make sure the builder doesn’t actually modify the original binaries; otherwise we’re breaking the license. For instance, the NVIDIA X11 drivers can be redistributed unmodified, but our builder applies patchelf
to make them work. Thus, its license is "unfree"
and it cannot be included in the Nixpkgs channel.
lib.licenses.unfree
, "unfree"
Unfree package that cannot be redistributed. You can build it yourself, but you cannot redistribute the output of the derivation. Thus it cannot be included in the Nixpkgs channel.
lib.licenses.unfreeRedistributableFirmware
, "unfree-redistributable-firmware"
This package supplies unfree, redistributable firmware. This is a separate value from unfree-redistributable
because not everybody cares whether firmware is free.
The value of a package’s meta.sourceProvenance
attribute specifies the provenance of the package’s derivation outputs.
If a package contains elements that are not built from the original source by a nixpkgs derivation, the meta.sourceProvenance
attribute should be a list containing one or more value from lib.sourceTypes
defined in nixpkgs/lib/source-types.nix
.
Adding this information helps users who have needs related to build transparency and supply-chain security to gain some visibility into their installed software or set policy to allow or disallow installation based on source provenance.
The presence of a particular sourceType
in a package’s meta.sourceProvenance
list indicates that the package contains some components falling into that category, though the absence of that sourceType
does not guarantee the absence of that category of sourceType
in the package’s contents. A package with no meta.sourceProvenance
set implies it has no known sourceType
s other than fromSource
.
The meaning of the meta.sourceProvenance
attribute does not depend on the value of the meta.license
attribute.
lib.sourceTypes.fromSource
Package elements which are produced by a nixpkgs derivation which builds them from source code.
lib.sourceTypes.binaryNativeCode
Native code to be executed on the target system’s CPU, built by a third party. This includes packages which wrap a downloaded AppImage or Debian package.
lib.sourceTypes.binaryFirmware
Code to be executed on a peripheral device or embedded controller, built by a third party.
lib.sourceTypes.binaryBytecode
Code to run on a VM interpreter or JIT compiled into bytecode by a third party. This includes packages which download Java .jar
files from another source.
Table of Contents
As opposed to most other mkDerivation
input attributes, passthru
is not passed to the derivation’s builder
executable.
Changing it will not trigger a rebuild – it is “passed through”.
Its value can be accessed as if it was set inside a derivation.
passthru
attributes follow no particular schema, but there are a few conventional patterns.
passthru
attributes{ stdenv, fetchGit }:
let
hello = stdenv.mkDerivation {
pname = "hello";
src = fetchGit { /* ... */ };
passthru = {
foo = "bar";
baz = {
value1 = 4;
value2 = 5;
};
};
};
in
hello.baz.value1
4
passthru
-attributes Many passthru
attributes are situational, so this section only lists recurring patterns.
They fall in one of these categories:
Global conventions, which are applied almost universally in Nixpkgs.
Generally these don’t entail any special support built into the derivation they belong to.
Common examples of this type are passthru.tests
and passthru.updateScript
.
Conventions for adding extra functionality to a derivation.
These tend to entail support from the derivation or the passthru
attribute in question.
Common examples of this type are passthru.optional-dependencies
, passthru.withPlugins
, and passthru.withPackages
.
All of those allow associating the package with a set of components built for that specific package, such as when building Python runtime environments using (python.withPackages
)[#python.withpackages-function].
Attributes that apply only to particular build helpers or language ecosystems are documented there.
passthru.tests
An attribute set with tests as values. A test is a derivation that builds when the test passes and fails to build otherwise.
Run these tests with:
$ cd path/to/nixpkgs
$ nix-build -A your-package.tests
The Nixpkgs systems for continuous integration Hydra and nixpkgs-review
don’t build these derivations by default, and (@ofborg
) only builds them when evaluating pull requests for that particular package, or when manually instructed.
Besides tests provided by upstream, that you run in the checkPhase
, you may want to define tests derivations in the passthru.tests
attribute, which won’t change the build. passthru.tests
have several advantages over running tests during any of the standard phases:
They access the package as consumers would, independently from the environment in which it was built
They can be run and debugged without rebuilding the package, which is useful if that takes a long time
They don’t add overhead to each build, as opposed checks added to the installCheckPhase
, such as versionCheckHook
.
It is also possible to use passthru.tests
to test the version with testVersion
, but since that is pretty trivial and recommended thing to do, we recommend using versionCheckHook
for that, which has the following advantages over passthru.tests
:
If the versionCheckPhase
(the phase defined by versionCheckHook
) fails, it triggers a failure which can’t be ignored if you use the package, or if you find out about it in a nixpkgs-review
report.
Sometimes packages become silently broken - meaning they fail to launch but their build passes because they don’t perform any tests in the checkPhase
. If you use this tool infrequently, such a silent breakage may rot in your system / profile configuration, and you will not notice the failure until you will want to use this package. Testing such basic functionality ensures you have to deal with the failure when you update your system / profile.
When you open a PR, ofborg’s CI will run passthru.tests
of packages that are directly changed by your PR (according to your commits’ messages), but if you’d want to use the @ofborg build
command for dependent packages, you won’t have to specify in addition the .tests
attribute of the packages you want to build, and no body will be able to avoid these tests.
For more on how to write and run package tests for Nixpkgs, see the testing section in the package contributor guide.
Tests written for NixOS are available as the nixosTests
argument to package recipes.
For instance, the OpenSMTPD derivation includes lines similar to:
{ nixosTests, ... }:
{
# ...
passthru.tests = {
basic-functionality-and-dovecot-integration = nixosTests.opensmtpd;
};
}
NixOS tests run in a virtual machine (VM), so they are slower than regular package tests. For more information see the NixOS manual on NixOS module tests.
passthru.updateScript
Nixpkgs tries to automatically update all packages that have an passthru.updateScript
attribute.
See the section on automatic package updates in the package contributor guide for details.
Table of Contents
The Nix language allows a derivation to produce multiple outputs, which is similar to what is utilized by other Linux distribution packaging systems. The outputs reside in separate Nix store paths, so they can be mostly handled independently of each other, including passing to build inputs, garbage collection or binary substitution. The exception is that building from source always produces all the outputs.
The main motivation is to save disk space by reducing runtime closure sizes; consequently also sizes of substituted binaries get reduced. Splitting can be used to have more granular runtime dependencies, for example the typical reduction is to split away development-only files, as those are typically not needed during runtime. As a result, closure sizes of many packages can get reduced to a half or even much less.
The reduction effects could be instead achieved by building the parts in completely separate derivations. That would often additionally reduce build-time closures, but it tends to be much harder to write such derivations, as build systems typically assume all parts are being built at once. This compromise approach of single source package producing multiple binary packages is also utilized often by rpm and deb.
A number of attributes can be used to work with a derivation with multiple outputs.
The attribute outputs
is a list of strings, which are the names of the outputs.
For each of these names, an identically named attribute is created, corresponding to that output.
The attribute meta.outputsToInstall
is used to determine the default set of outputs to install when using the derivation name unqualified:
bin
, or out
, or the first specified output; as well as man
if that is specified.
In the Nix language the individual outputs can be reached explicitly as attributes, e.g. coreutils.info
, but the typical case is just using packages as build inputs.
When a multiple-output derivation gets into a build input of another derivation, the dev
output is added if it exists, otherwise the first output is added. In addition to that, propagatedBuildOutputs
of that package which by default contain $outputBin
and $outputLib
are also added. (See the section called “File type groups”.)
In some cases it may be desirable to combine different outputs under a single store path. The symlinkJoin
builder can be used to do this. (See the section called “symlinkJoin
”). Note that this may negate some closure size benefits of using a multiple-output package.
Here you find how to write a derivation that produces multiple outputs.
In nixpkgs there is a framework supporting multiple-output derivations. It tries to cover most cases by default behavior. You can find the source separated in <nixpkgs/pkgs/build-support/setup-hooks/multiple-outputs.sh>
; it’s relatively well-readable. The whole machinery is triggered by defining the outputs
attribute to contain the list of desired output names (strings).
{
outputs = [ "bin" "dev" "out" "doc" ];
}
Often such a single line is enough. For each output an equally named environment variable is passed to the builder and contains the path in nix store for that output. Typically you also want to have the main out
output, as it catches any files that didn’t get elsewhere.
There is a special handling of the debug
output, described at the section called “separateDebugInfo
”.
A commonly adopted convention in nixpkgs
is that executables provided by the package are contained within its first output. This convention allows the dependent packages to reference the executables provided by packages in a uniform manner. For instance, provided with the knowledge that the perl
package contains a perl
executable it can be referenced as ${pkgs.perl}/bin/perl
within a Nix derivation that needs to execute a Perl script.
The glibc
package is a deliberate single exception to the “binaries first” convention. The glibc
has libs
as its first output allowing the libraries provided by glibc
to be referenced directly (e.g. ${glibc}/lib/ld-linux-x86-64.so.2
). The executables provided by glibc
can be accessed via its bin
attribute (e.g. ${lib.getBin stdenv.cc.libc}/bin/ldd
).
The reason for why glibc
deviates from the convention is because referencing a library provided by glibc
is a very common operation among Nix packages. For instance, third-party executables packaged by Nix are typically patched and relinked with the relevant version of glibc
libraries from Nix packages (please see the documentation on patchelf for more details).
The support code currently recognizes some particular kinds of outputs and either instructs the build system of the package to put files into their desired outputs or it moves the files during the fixup phase. Each group of file types has an outputFoo
variable specifying the output name where they should go. If that variable isn’t defined by the derivation writer, it is guessed – a default output name is defined, falling back to other possibilities if the output isn’t defined.
$outputDev
is for development-only files. These include C(++) headers (include/
), pkg-config (lib/pkgconfig/
), cmake (lib/cmake/
) and aclocal files (share/aclocal/
). They go to dev
or out
by default.
$outputBin
is meant for user-facing binaries, typically residing in bin/
. They go to bin
or out
by default.
$outputLib
is meant for libraries, typically residing in lib/
and libexec/
. They go to lib
or out
by default.
$outputDoc
is for user documentation, typically residing in share/doc/
. It goes to doc
or out
by default.
$outputDevdoc
is for developer documentation. Currently we count gtk-doc and devhelp books, typically residing in share/gtk-doc/
and share/devhelp/
, in there. It goes to devdoc
or is removed (!) by default. This is because e.g. gtk-doc tends to be rather large and completely unused by nixpkgs users.
$outputMan
is for man pages (except for section 3), typically residing in share/man/man[0-9]/
. They go to man
or $outputBin
by default.
$outputDevman
is for section 3 man pages, typically residing in share/man/man[0-9]/
. They go to devman
or $outputMan
by default.
$outputInfo
is for info pages, typically residing in share/info/
. They go to info
or $outputBin
by default.
Some configure scripts don’t like some of the parameters passed by default by the framework, e.g. --docdir=/foo/bar
. You can disable this by setting setOutputFlags = false;
.
The outputs of a single derivation can retain references to each other, but note that circular references are not allowed. (And each strongly-connected component would act as a single output anyway.)
Most of split packages contain their core functionality in libraries. These libraries tend to refer to various kind of data that typically gets into out
, e.g. locale strings, so there is often no advantage in separating the libraries into lib
, as keeping them in out
is easier.
Some packages have hidden assumptions on install paths, which complicates splitting.
Table of Contents
“Cross-compilation” means compiling a program on one machine for another type of machine. For example, a typical use of cross-compilation is to compile programs for embedded devices. These devices often don’t have the computing power and memory to compile their own programs. One might think that cross-compilation is a fairly niche concern. However, there are significant advantages to rigorously distinguishing between build-time and run-time environments! Significant, because the benefits apply even when one is developing and deploying on the same machine. Nixpkgs is increasingly adopting the opinion that packages should be written with cross-compilation in mind, and Nixpkgs should evaluate in a similar way (by minimizing cross-compilation-specific special cases) whether or not one is cross-compiling.
This chapter will be organized in three parts. First, it will describe the basics of how to package software in a way that supports cross-compilation. Second, it will describe how to use Nixpkgs when cross-compiling. Third, it will describe the internal infrastructure supporting cross-compilation.
Nixpkgs follows the conventions of GNU autoconf. We distinguish between 3 types of platforms when building a derivation: build, host, and target. In summary, build is the platform on which a package is being built, host is the platform on which it will run. The third attribute, target, is relevant only for certain specific compilers and build tools.
In Nixpkgs, these three platforms are defined as attribute sets under the names buildPlatform
, hostPlatform
, and targetPlatform
. They are always defined as attributes in the standard environment. That means one can access them like:
{ stdenv, fooDep, barDep, ... }: {
# ...stdenv.buildPlatform...
}
buildPlatform
The “build platform” is the platform on which a package is built. Once someone has a built package, or pre-built binary package, the build platform should not matter and can be ignored.
hostPlatform
The “host platform” is the platform on which a package will be run. This is the simplest platform to understand, but also the one with the worst name.
targetPlatform
The “target platform” attribute is, unlike the other two attributes, not actually fundamental to the process of building software. Instead, it is only relevant for compatibility with building certain specific compilers and build tools. It can be safely ignored for all other packages.
The build process of certain compilers is written in such a way that the compiler resulting from a single build can itself only produce binaries for a single platform. The task of specifying this single “target platform” is thus pushed to build time of the compiler. The root cause of this is that the compiler (which will be run on the host) and the standard library/runtime (which will be run on the target) are built by a single build process.
There is no fundamental need to think about a single target ahead of time like this. If the tool supports modular or pluggable backends, both the need to specify the target at build time and the constraint of having only a single target disappear. An example of such a tool is LLVM.
Although the existence of a “target platform” is arguably a historical mistake, it is a common one: examples of tools that suffer from it are GCC, Binutils, GHC and Autoconf. Nixpkgs tries to avoid sharing in the mistake where possible. Still, because the concept of a target platform is so ingrained, it is best to support it as is.
The exact schema these fields follow is a bit ill-defined due to a long and convoluted evolution, but this is slowly being cleaned up. You can see examples of ones used in practice in lib.systems.examples
; note how they are not all very consistent. For now, here are few fields can count on them containing:
system
This is a two-component shorthand for the platform. Examples of this would be “x86_64-darwin” and “i686-linux”; see lib.systems.doubles
for more. The first component corresponds to the CPU architecture of the platform and the second to the operating system of the platform ([cpu]-[os]
). This format has built-in support in Nix, such as the builtins.currentSystem
impure string.
config
This is a 3- or 4- component shorthand for the platform. Examples of this would be x86_64-unknown-linux-gnu
and aarch64-apple-darwin14
. This is a standard format called the “LLVM target triple”, as they are pioneered by LLVM. In the 4-part form, this corresponds to [cpu]-[vendor]-[os]-[abi]
. This format is strictly more informative than the “Nix host double”, as the previous format could analogously be termed. This needs a better name than config
!
parsed
This is a Nix representation of a parsed LLVM target triple with white-listed components. This can be specified directly, or actually parsed from the config
. See lib.systems.parse
for the exact representation.
libc
This is a string identifying the standard C library used. Valid identifiers include “glibc” for GNU libc, “libSystem” for Darwin’s Libsystem, and “uclibc” for µClibc. It should probably be refactored to use the module system, like parse
.
is*
These predicates are defined in lib.systems.inspect
, and slapped onto every platform. They are superior to the ones in stdenv
as they force the user to be explicit about which platform they are inspecting. Please use these instead of those.
platform
This is, quite frankly, a dumping ground of ad-hoc settings (it’s an attribute set). See lib.systems.platforms
for examples—there’s hopefully one in there that will work verbatim for each platform that is working. Please help us triage these flags and give them better homes!
This is a rather philosophical description that isn’t very Nixpkgs-specific. For an overview of all the relevant attributes given to mkDerivation
, see the section called “Specifying dependencies”. For a description of how everything is implemented, see the section called “Implementation of dependencies”.
In this section we explore the relationship between both runtime and build-time dependencies and the 3 Autoconf platforms.
A run time dependency between two packages requires that their host platforms match. This is directly implied by the meaning of “host platform” and “runtime dependency”: The package dependency exists while both packages are running on a single host platform.
A build time dependency, however, has a shift in platforms between the depending package and the depended-on package. “build time dependency” means that to build the depending package we need to be able to run the depended-on’s package. The depending package’s build platform is therefore equal to the depended-on package’s host platform.
If both the dependency and depending packages aren’t compilers or other machine-code-producing tools, we’re done. And indeed buildInputs
and nativeBuildInputs
have covered these simpler cases for many years. But if the dependency does produce machine code, we might need to worry about its target platform too. In principle, that target platform might be any of the depending package’s build, host, or target platforms, but we prohibit dependencies from a “later” platform to an earlier platform to limit confusion because we’ve never seen a legitimate use for them.
Finally, if the depending package is a compiler or other machine-code-producing tool, it might need dependencies that run at “emit time”. This is for compilers that (regrettably) insist on being built together with their source languages’ standard libraries. Assuming build != host != target, a run-time dependency of the standard library cannot be run at the compiler’s build time or run time, but only at the run time of code emitted by the compiler.
Putting this all together, that means that we have dependency types of the form “X→ E”, which means that the dependency executes on X and emits code for E; each of X and E can be build
, host
, or target
, and E can be *
to indicate that the dependency is not a compiler-like package.
Dependency types describe the relationships that a package has with each of its transitive dependencies. You could think of attaching one or more dependency types to each of the formal parameters at the top of a package’s .nix
file, as well as to all of their formal parameters, and so on. Triples like (foo, bar, baz)
, on the other hand, are a property of an instantiated derivation – you could would attach a triple (mips-linux, mips-linux, sparc-solaris)
to a .drv
file in /nix/store
.
Only nine dependency types matter in practice:
Dependency type | Dependency’s host platform | Dependency’s target platform |
---|---|---|
build → * | build | (none) |
build → build | build | build |
build → host | build | host |
build → target | build | target |
host → * | host | (none) |
host → host | host | host |
host → target | host | target |
target → * | target | (none) |
target → target | target | target |
Let’s use g++
as an example to make this table clearer. g++
is a C++ compiler written in C. Suppose we are building g++
with a (build, host, target)
platform triple of (foo, bar, baz)
. This means we are using a foo
-machine to build a copy of g++
which will run on a bar
-machine and emit binaries for the baz
-machine.
g++
links against the host platform’s glibc
C library, which is a “host→ *” dependency with a triple of (bar, bar, *)
. Since it is a library, not a compiler, it has no “target”.
Since g++
is written in C, the gcc
compiler used to compile it is a “build→ host” dependency of g++
with a triple of (foo, foo, bar)
. This compiler runs on the build platform and emits code for the host platform.
gcc
links against the build platform’s glibc
C library, which is a “build→ *” dependency with a triple of (foo, foo, *)
. Since it is a library, not a compiler, it has no “target”.
This gcc
is itself compiled by an earlier copy of gcc
. This earlier copy of gcc
is a “build→ build” dependency of g++
with a triple of (foo, foo, foo)
. This “early gcc
” runs on the build platform and emits code for the build platform.
g++
is bundled with libgcc
, which includes a collection of target-machine routines for exception handling and
software floating point emulation. libgcc
would be a “target→ *” dependency with triple (foo, baz, *)
, because it consists of machine code which gets linked against the output of the compiler that we are building. It is a library, not a compiler, so it has no target of its own.
libgcc
is written in C and compiled with gcc
. The gcc
that compiles it will be a “build→ target” dependency with triple (foo, foo, baz)
. It gets compiled and run at g++
-build-time (on platform foo
), but must emit code for the baz
-platform.
g++
allows inline assembler code, so it depends on access to a copy of the gas
assembler. This would be a “host→ target” dependency with triple (foo, bar, baz)
.
g++
(and gcc
) include a library libgccjit.so
, which wrap the compiler in a library to create a just-in-time compiler. In nixpkgs, this library is in the libgccjit
package; if C++ required that programs have access to a JIT, g++
would need to add a “target→ target” dependency for libgccjit
with triple (foo, baz, baz)
. This would ensure that the compiler ships with a copy of libgccjit
which both executes on and generates code for the baz
-platform.
If g++
itself linked against libgccjit.so
(for example, to allow compile-time-evaluated C++ expressions), then the libgccjit
package used to provide this functionality would be a “host→ host” dependency of g++
: it is code which runs on the host
and emits code for execution on the host
.
Some frequently encountered problems when packaging for cross-compilation should be answered here. Ideally, the information above is exhaustive, so this section cannot provide any new information, but it is ludicrous and cruel to expect everyone to spend effort working through the interaction of many features just to figure out the same answer to the same common problem. Feel free to add to this list!
cc
/ar
/ld
etc.) Many packages assume that an unprefixed binutils (cc
/ar
/ld
etc.) is available, but Nix doesn’t provide one. It only provides a prefixed one, just as it only does for all the other binutils programs. It may be necessary to patch the package to fix the build system to use a prefix. For instance, instead of cc
, use ${stdenv.cc.targetPrefix}cc
.
{
makeFlags = [ "CC=${stdenv.cc.targetPrefix}cc" ];
}
On less powerful machines, it can be inconvenient to cross-compile a package only to find out that GCC has to be compiled from source, which could take up to several hours. Nixpkgs maintains a limited cross-related jobset on Hydra, which tests cross-compilation to various platforms from build platforms “x86_64-darwin”, “x86_64-linux”, and “aarch64-linux”. See pkgs/top-level/release-cross.nix
for the full list of target platforms and packages. For instance, the following invocation fetches the pre-built cross-compiled GCC for armv6l-unknown-linux-gnueabihf
and builds GNU Hello from source.
$ nix-build '<nixpkgs>' -A pkgsCross.raspberryPi.hello
Add the following to your mkDerivation
invocation.
{
depsBuildBuild = [ buildPackages.stdenv.cc ];
}
Add the following to your mkDerivation
invocation.
{
doCheck = stdenv.buildPlatform.canExecute stdenv.hostPlatform;
}
Add mesonEmulatorHook
to nativeBuildInputs
conditionally on if the target binaries can be executed.
e.g.
{
nativeBuildInputs = [
meson
] ++ lib.optionals (!stdenv.buildPlatform.canExecute stdenv.hostPlatform) [
mesonEmulatorHook
];
}
Example of an error which this fixes.
[Errno 8] Exec format error: './gdk3-scan'
-static
outside a isStatic
platform. Add stdenv.cc.libc.static
(static output of glibc) to buildInputs
conditionally on if hostPlatform
uses glibc
.
e.g.
{
buildInputs = lib.optionals (stdenv.hostPlatform.libc == "glibc") [ stdenv.cc.libc.static ];
}
Examples of errors which this fixes.
cannot find -lm: No such file or directory
cannot find -lc: No such file or directory
At the time of writing it is assumed the issue only happens on glibc
because it splits the static libraries in to a different output.
You may want to look in to using stdenvAdapters.makeStatic
or pkgsStatic
or a isStatic = true
platform.
Nixpkgs can be instantiated with localSystem
alone, in which case there is no cross-compiling and everything is built by and for that system, or also with crossSystem
, in which case packages run on the latter, but all building happens on the former. Both parameters take the same schema as the 3 (build, host, and target) platforms defined in the previous section. As mentioned above, lib.systems.examples
has some platforms which are used as arguments for these parameters in practice. You can use them programmatically, or on the command line:
$ nix-build '<nixpkgs>' --arg crossSystem '(import <nixpkgs/lib>).systems.examples.fooBarBaz' -A whatever
Eventually we would like to make these platform examples an unnecessary convenience so that
$ nix-build '<nixpkgs>' --arg crossSystem '{ config = "<arch>-<os>-<vendor>-<abi>"; }' -A whatever
works in the vast majority of cases. The problem today is dependencies on other sorts of configuration which aren’t given proper defaults. We rely on the examples to crudely to set those configuration parameters in some vaguely sane manner on the users behalf. Issue #34274 tracks this inconvenience along with its root cause in crufty configuration options.
While one is free to pass both parameters in full, there’s a lot of logic to fill in missing fields. As discussed in the previous section, only one of system
, config
, and parsed
is needed to infer the other two. Additionally, libc
will be inferred from parse
. Finally, localSystem.system
is also impurely inferred based on the platform evaluation occurs. This means it is often not necessary to pass localSystem
at all, as in the command-line example in the previous paragraph.
Many sources (manual, wiki, etc) probably mention passing system
, platform
, along with the optional crossSystem
to Nixpkgs: import <nixpkgs> { system = ..; platform = ..; crossSystem = ..; }
. Passing those two instead of localSystem
is still supported for compatibility, but is discouraged. Indeed, much of the inference we do for these parameters is motivated by compatibility as much as convenience.
One would think that localSystem
and crossSystem
overlap horribly with the three *Platforms
(buildPlatform
, hostPlatform,
and targetPlatform
; see stage.nix
or the manual). Actually, those identifiers are purposefully not used here to draw a subtle but important distinction: While the granularity of having 3 platforms is necessary to properly build packages, it is overkill for specifying the user’s intent when making a build plan or package set. A simple “build vs deploy” dichotomy is adequate: the sliding window principle described in the previous section shows how to interpolate between the these two “end points” to get the 3 platform triple for each bootstrapping stage. That means for any package a given package set, even those not bound on the top level but only reachable via dependencies or buildPackages
, the three platforms will be defined as one of localSystem
or crossSystem
, with the former replacing the latter as one traverses build-time dependencies. A last simple difference is that crossSystem
should be null when one doesn’t want to cross-compile, while the *Platform
s are always non-null. localSystem
is always non-null.
The categories of dependencies developed in the section called “Theory of dependency categorization” are specified as lists of derivations given to mkDerivation
, as documented in the section called “Specifying dependencies”. In short, each list of dependencies for “host → target” is called deps<host><target>
(where host
, and target
values are either build
, host
, or target
), with exceptions for backwards compatibility that depsBuildHost
is instead called nativeBuildInputs
and depsHostTarget
is instead called buildInputs
. Nixpkgs is now structured so that each deps<host><target>
is automatically taken from pkgs<host><target>
. (These pkgs<host><target>
s are quite new, so there is no special case for nativeBuildInputs
and buildInputs
.) For example, pkgsBuildHost.gcc
should be used at build-time, while pkgsHostTarget.gcc
should be used at run-time.
Now, for most of Nixpkgs’s history, there were no pkgs<host><target>
attributes, and most packages have not been refactored to use it explicitly. Prior to those, there were just buildPackages
, pkgs
, and targetPackages
. Those are now redefined as aliases to pkgsBuildHost
, pkgsHostTarget
, and pkgsTargetTarget
. It is acceptable, even recommended, to use them for libraries to show that the host platform is irrelevant.
But before that, there was just pkgs
, even though both buildInputs
and nativeBuildInputs
existed. [Cross barely worked, and those were implemented with some hacks on mkDerivation
to override dependencies.] What this means is the vast majority of packages do not use any explicit package set to populate their dependencies, just using whatever callPackage
gives them even if they do correctly sort their dependencies into the multiple lists described above. And indeed, asking that users both sort their dependencies, and take them from the right attribute set, is both too onerous and redundant, so the recommended approach (for now) is to continue just categorizing by list and not using an explicit package set.
To make this work, we “splice” together the six pkgsFooBar
package sets and have callPackage
actually take its arguments from that. This is currently implemented in pkgs/top-level/splice.nix
. mkDerivation
then, for each dependency attribute, pulls the right derivation out from the splice. This splicing can be skipped when not cross-compiling as the package sets are the same, but still is a bit slow for cross-compiling. We’d like to do something better, but haven’t come up with anything yet.
Each of the package sets described above come from a single bootstrapping stage. While pkgs/top-level/default.nix
, coordinates the composition of stages at a high level, pkgs/top-level/stage.nix
“ties the knot” (creates the fixed point) of each stage. The package sets are defined per-stage however, so they can be thought of as edges between stages (the nodes) in a graph. Compositions like pkgsBuildTarget.targetPackages
can be thought of as paths to this graph.
While there are many package sets, and thus many edges, the stages can also be arranged in a linear chain. In other words, many of the edges are redundant as far as connectivity is concerned. This hinges on the type of bootstrapping we do. Currently for cross it is:
(native, native, native)
(native, native, foreign)
(native, foreign, foreign)
In each stage, pkgsBuildHost
refers to the previous stage, pkgsBuildBuild
refers to the one before that, and pkgsHostTarget
refers to the current one, and pkgsTargetTarget
refers to the next one. When there is no previous or next stage, they instead refer to the current stage. Note how all the invariants regarding the mapping between dependency and depending packages’ build host and target platforms are preserved. pkgsBuildTarget
and pkgsHostHost
are more complex in that the stage fitting the requirements isn’t always a fixed chain of “prevs” and “nexts” away (modulo the “saturating” self-references at the ends). We just special case each instead. All the primary edges are implemented is in pkgs/stdenv/booter.nix
, and secondarily aliases in pkgs/top-level/stage.nix
.
The native stages are bootstrapped in legacy ways that predate the current cross implementation. This is why the bootstrapping stages leading up to the final stages are ignored in the previous paragraph.
If one looks at the 3 platform triples, one can see that they overlap such that one could put them together into a chain like:
(native, native, native, foreign, foreign)
If one imagines the saturating self references at the end being replaced with infinite stages, and then overlays those platform triples, one ends up with the infinite tuple:
(native..., native, native, native, foreign, foreign, foreign...)
One can then imagine any sequence of platforms such that there are bootstrap stages with their 3 platforms determined by “sliding a window” that is the 3 tuple through the sequence. This was the original model for bootstrapping. Without a target platform (assume a better world where all compilers are multi-target and all standard libraries are built in their own derivation), this is sufficient. Conversely if one wishes to cross compile “faster”, with a “Canadian Cross” bootstrapping stage where build != host != target
, more bootstrapping stages are needed since no sliding window provides the pesky pkgsBuildTarget
package set since it skips the Canadian cross stage’s “host”.
It is much better to refer to buildPackages
than targetPackages
, or more broadly package sets that do not mention “target”. There are three reasons for this.
First, it is because bootstrapping stages do not have a unique targetPackages
. For example a (x86-linux, x86-linux, arm-linux)
and (x86-linux, x86-linux, x86-windows)
package set both have a (x86-linux, x86-linux, x86-linux)
package set. Because there is no canonical targetPackages
for such a native (build == host == target
) package set, we set their targetPackages
Second, it is because this is a frequent source of hard-to-follow “infinite recursions” / cycles. When only package sets that don’t mention target are used, the package set forms a directed acyclic graph. This means that all cycles that exist are confined to one stage. This means they are a lot smaller, and easier to follow in the code or a backtrace. It also means they are present in native and cross builds alike, and so more likely to be caught by CI and other users.
Thirdly, it is because everything target-mentioning only exists to accommodate compilers with lousy build systems that insist on the compiler itself and standard library being built together. Of course that is bad because bigger derivations means longer rebuilds. It is also problematic because it tends to make the standard libraries less like other libraries than they could be, complicating code and build systems alike. Because of the other problems, and because of these innate disadvantages, compilers ought to be packaged another way where possible.
If one explores Nixpkgs, they will see derivations with names like gccCross
. Such *Cross
derivations is a holdover from before we properly distinguished between the host and target platforms—the derivation with “Cross” in the name covered the build = host != target
case, while the other covered the host = target
, with build platform the same or not based on whether one was using its .__spliced.buildHost
or .__spliced.hostTarget
.
Table of Contents
Some common issues when packaging software for Darwin:
The Darwin stdenv
uses clang instead of gcc. When referring to the compiler $CC
or cc
will work in both cases. Some builds hardcode gcc/g++ in their build scripts, that can usually be fixed with using something like makeFlags = [ "CC=cc" ];
or by patching the build scripts.
stdenv.mkDerivation {
name = "libfoo-1.2.3";
# ...
buildPhase = ''
$CC -o hello hello.c
'';
}
On Darwin, libraries are linked using absolute paths, libraries are resolved by their install_name
at link time. Sometimes packages won’t set this correctly causing the library lookups to fail at runtime. This can be fixed by adding extra linker flags or by running install_name_tool -id
during the fixupPhase
.
stdenv.mkDerivation {
name = "libfoo-1.2.3";
# ...
makeFlags = lib.optional stdenv.hostPlatform.isDarwin "LDFLAGS=-Wl,-install_name,$(out)/lib/libfoo.dylib";
}
Even if the libraries are linked using absolute paths and resolved via their install_name
correctly, tests can sometimes fail to run binaries. This happens because the checkPhase
runs before the libraries are installed.
This can usually be solved by running the tests after the installPhase
or alternatively by using DYLD_LIBRARY_PATH
. More information about this variable can be found in the dyld(1) manpage.
dyld: Library not loaded: /nix/store/7hnmbscpayxzxrixrgxvvlifzlxdsdir-jq-1.5-lib/lib/libjq.1.dylib
Referenced from: /private/tmp/nix-build-jq-1.5.drv-0/jq-1.5/tests/../jq
Reason: image not found
./tests/jqtest: line 5: 75779 Abort trap: 6
stdenv.mkDerivation {
name = "libfoo-1.2.3";
# ...
doInstallCheck = true;
installCheckTarget = "check";
}
Some packages assume xcode is available and use xcrun
to resolve build tools like clang
, etc. This causes errors like xcode-select: error: no developer tools were found at '/Applications/Xcode.app'
while the build doesn’t actually depend on xcode.
stdenv.mkDerivation {
name = "libfoo-1.2.3";
# ...
prePatch = ''
substituteInPlace Makefile \
--replace-fail '/usr/bin/xcrun clang' clang
'';
}
The package xcbuild
can be used to build projects that really depend on Xcode. However, this replacement is not 100% compatible with Xcode and can occasionally cause issues.
x86_64-darwin uses the 10.12 SDK by default, but some software is not compatible with that version of the SDK. In that case,
the 11.0 SDK used by aarch64-darwin is available for use on x86_64-darwin. To use it, reference apple_sdk_11_0
instead of
apple_sdk
in your derivation and use pkgs.darwin.apple_sdk_11_0.callPackage
instead of pkgs.callPackage
. On Linux, this will
have the same effect as pkgs.callPackage
, so you can use pkgs.darwin.apple_sdk_11_0.callPackage
regardless of platform.
A build helper is a function that produces derivations.
This is not to be confused with the builder
argument of the Nix derivation
primitive, which refers to the executable that produces the build result, or remote builder, which refers to a remote machine that could run such an executable.
Such a function is usually designed to abstract over a typical workflow for a given programming language or framework.
This allows declaring a build recipe by setting a limited number of options relevant to the particular use case instead of using the derivation
function directly.
stdenv.mkDerivation
is the most widely used build helper, and serves as a basis for many others.
In addition, it offers various options to customize parts of the builds.
There is no uniform interface for build helpers.
Trivial build helpers and fetchers have various input types for convenience.
Language- or framework-specific build helpers usually follow the style of stdenv.mkDerivation
, which accepts an attribute set or a fixed-point function taking an attribute set.
Table of Contents
fetchurl
fetchzip
fetchpatch
fetchDebianPatch
fetchsvn
fetchgit
fetchfossil
fetchcvs
fetchhg
fetchFromGitea
fetchFromGitHub
fetchFromGitLab
fetchFromGitiles
fetchFromBitbucket
fetchFromSavannah
fetchFromRepoOrCz
fetchFromSourcehut
requireFile
fetchtorrent
Building software with Nix often requires downloading source code and other files from the internet. To this end, we use functions that we call fetchers, which obtain remote sources via various protocols and services.
Nix provides built-in fetchers such as builtins.fetchTarball
.
Nixpkgs provides its own fetchers, which work differently:
A built-in fetcher will download and cache files at evaluation time and produce a store path. A Nixpkgs fetcher will create a (fixed-output) derivation, and files are downloaded at build time.
Built-in fetchers will invalidate their cache after tarball-ttl
expires, and will require network activity to check if the cache entry is up to date.
Nixpkgs fetchers only re-download if the specified hash changes or the store object is not available.
Built-in fetchers do not use substituters. Derivations produced by Nixpkgs fetchers will use any configured binary cache transparently.
This significantly reduces the time needed to evaluate Nixpkgs, and allows Hydra to retain and re-distribute sources used by Nixpkgs in the public binary cache. For these reasons, Nix’s built-in fetchers are not allowed in Nixpkgs.
The following table summarises the differences:
Fetchers | Download | Output | Cache | Re-download when |
---|---|---|---|---|
builtins.fetch* | evaluation time | store path | /nix/store , ~/.cache/nix | tarball-ttl expires, cache miss in ~/.cache/nix , output store object not in local store |
pkgs.fetch* | build time | derivation | /nix/store , substituters | output store object not available |
pkgs.fetchFrom*
helpers retrieve snapshots of version-controlled sources, as opposed to the entire version history, which is more efficient.
pkgs.fetchgit
by default also has the same behaviour, but can be changed through specific attributes given to it.
Because Nixpkgs fetchers are fixed-output derivations, an output hash has to be specified, usually indirectly through a hash
attribute.
This hash refers to the derivation output, which can be different from the remote source itself!
This has the following implications that you should be aware of:
Use Nix (or Nix-aware) tooling to produce the output hash.
When changing any fetcher parameters, always update the output hash. Use one of the methods from the section called “Updating source hashes”. Otherwise, existing store objects that match the output hash will be re-used rather than fetching new content.
A similar problem arises while testing changes to a fetcher’s implementation.
If the output of the derivation already exists in the Nix store, test failures can go undetected.
The invalidateFetcherByDrvHash
function helps prevent reusing cached derivations.
There are several ways to obtain the hash corresponding to a remote source. Unless you understand how the fetcher you’re using calculates the hash from the downloaded contents, you should use the fake hash method.
The fake hash method: In your package recipe, set the hash to one of
""
lib.fakeHash
lib.fakeSha256
lib.fakeSha512
Attempt to build, extract the calculated hashes from error messages, and put them into the recipe.
You must use one of these four fake hashes and not some arbitrarily-chosen hash. See the section called “Obtaining hashes securely” for details.
Consider the following recipe that produces a plain file:
{ fetchurl }:
fetchurl {
url = "https://raw.githubusercontent.com/NixOS/nixpkgs/23.05/.version";
hash = "sha256-ZHl1emidXVojm83LCVrwULpwIzKE/mYwfztVkvpruOM=";
}
A common mistake is to update a fetcher parameter, such as url
, without updating the hash:
{ fetchurl }:
fetchurl {
url = "https://raw.githubusercontent.com/NixOS/nixpkgs/23.11/.version";
hash = "sha256-ZHl1emidXVojm83LCVrwULpwIzKE/mYwfztVkvpruOM=";
}
This will produce the same output as before! Set the hash to an empty string:
{ fetchurl }:
fetchurl {
url = "https://raw.githubusercontent.com/NixOS/nixpkgs/23.11/.version";
hash = "";
}
When building the package, use the error message to determine the correct hash:
$ nix-build
(some output removed for clarity)
error: hash mismatch in fixed-output derivation '/nix/store/7yynn53jpc93l76z9zdjj4xdxgynawcw-version.drv':
specified: sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=
got: sha256-BZqI7r0MNP29yGH5+yW2tjU9OOpOCEvwWKrWCv5CQ0I=
error: build of '/nix/store/bqdjcw5ij5ymfbm41dq230chk9hdhqff-version.drv' failed
Prefetch the source with nix-prefetch-<type> <URL>
, where <type>
is one of
url
git
hg
cvs
bzr
svn
The hash is printed to stdout.
Prefetch by package source (with nix-prefetch-url '<nixpkgs>' -A <package>.src
, where <package>
is package attribute name).
The hash is printed to stdout.
This works well when you’ve upgraded the existing package version and want to find out new hash, but is useless if the package can’t be accessed by attribute or the package has multiple sources (.srcs
, architecture-dependent sources, etc).
Upstream hash: use it when upstream provides sha256
or sha512
.
Don’t use it when upstream provides md5
, compute sha256
instead.
A little nuance is that nix-prefetch-*
tools produce hashes with the nix32
encoding (a Nix-specific base32 adaptation), but upstream usually provides hexadecimal (base16
) encoding.
Fetchers understand both formats.
Nixpkgs does not standardise on any one format.
You can convert between hash formats with nix-hash
.
Extract the hash from a local source archive with sha256sum
.
Use nix-prefetch-url file:///path/to/archive
if you want the custom Nix base32
hash.
It’s always a good idea to avoid Man-in-the-Middle (MITM) attacks when downloading source contents. Otherwise, you could unknowingly download malware instead of the intended source, and instead of the actual source hash, you’ll end up using the hash of malware. Here are security considerations for this scenario:
http://
URLs are not secure to prefetch hashes.
Upstream hashes should be obtained via a secure protocol.
https://
URLs give you more protections when using nix-prefetch-*
or for upstream hashes.
https://
URLs are secure when using the fake hash method only if you use one of the listed fake hashes.
If you use any other hash, the download will be exposed to MITM attacks even if you use HTTPS URLs.
In more concrete terms, if you use any other hash, the --insecure
flag will be passed to the underlying call to curl
when downloading content.
Nixpkgs fetchers can make use of a http(s) proxy. Each fetcher will automatically inherit proxy-related environment variables (http_proxy
, https_proxy
,