Hacking

This section provides some notes on how to hack on Nix. To get the latest version of Nix from GitHub:

$ git clone https://github.com/NixOS/nix.git
$ cd nix

To build Nix for the current operating system/architecture use

$ nix-build

or if you have a flake-enabled nix:

$ nix build

This will build defaultPackage attribute defined in the flake.nix file. To build for other platforms add one of the following suffixes to it: aarch64-linux, i686-linux, x86_64-darwin, x86_64-linux. i.e.

$ nix-build -A defaultPackage.x86_64-linux

To build all dependencies and start a shell in which all environment variables are set up so that those dependencies can be found:

$ nix-shell

or if you have a flake-enabled nix:

$ nix develop

To get a shell with a different compilation environment (e.g. stdenv, gccStdenv, clangStdenv, clang11Stdenv):

$ nix-shell -A devShells.x86_64-linux.clang11StdenvPackages

or if you have a flake-enabled nix:

$ nix develop .#clang11StdenvPackages

To build Nix itself in this shell:

[nix-shell]$ ./bootstrap.sh
[nix-shell]$ ./configure $configureFlags --prefix=$(pwd)/outputs/out
[nix-shell]$ make -j $NIX_BUILD_CORES

To install it in $(pwd)/outputs and test it:

[nix-shell]$ make install
[nix-shell]$ make installcheck -j $NIX_BUILD_CORES
[nix-shell]$ ./outputs/out/bin/nix --version
nix (Nix) 3.0

If you have a flakes-enabled Nix you can replace:

$ nix-shell

by:

$ nix develop

Testing

Nix comes with three different flavors of tests: unit, functional and integration.

Unit-tests

The unit-tests for each Nix library (libexpr, libstore, etc..) are defined under src/{library_name}/tests using the googletest framework.

You can run the whole testsuite with make check, or the tests for a specific component with make libfoo-tests_RUN. Finer-grained filtering is also possible using the --gtest_filter command-line option.

Functional tests

The functional tests reside under the tests directory and are listed in tests/local.mk. The whole testsuite can be run with make install && make installcheck. Individual tests can be run with make tests/{testName}.sh.test.

Integration tests

The integration tests are defined in the Nix flake under the hydraJobs.tests attribute. These tests include everything that needs to interact with external services or run Nix in a non-trivial distributed setup. Because these tests are expensive and require more than what the standard github-actions setup provides, they only run on the master branch (on https://hydra.nixos.org/jobset/nix/master).

You can run them manually with nix build .#hydraJobs.tests.{testName} or nix-build -A hydraJobs.tests.{testName}