[Nix-dev] all-packages.nix and the unoverridable self.

[Daniel Peebles]

Did you figure this out? I'm curious whether something got messed up in the
recent changes.

On Mon, May 2, 2016 at 2:23 AM, <roconnor at theorem.ca> wrote:

> Something seems wrong / bizzare with the recursion in all-packages.nix
>
> I've been trying to override linux_4_4 in my configuration.nix with the
> following:
>
>      nixpkgs.config.packageOverrides = super:
>       { linux_4_4 = super.linux_4_4.override { extraConfig =
> "CHROME_PLATFORMS y";
>                                                kernelPatches = [ { name =
> "f10_sysrq"; patch = ./f10_sysrq.patch; } ]; };
>       };
>
> but this no longer works.  I've spent a few hours studying the issue.
> If I do the following chain of overrides upto the linuxPackages
> attribute
>
>      nixpkgs.config.packageOverrides = super: rec
>       { linux_4_4 = super.linux_4_4.override { extraConfig =
> "CHROME_PLATFORMS y";
>                                                kernelPatches = [ { name =
> "f10_sysrq"; patch = ./f10_sysrq.patch; } ]; };
>         linuxPackages_4_4 = super.recurseIntoAttrs (super.linuxPackagesFor
>         linux_4_4 linuxPackages_4_4);
>         linuxPackages = linuxPackages_4_4;
>         linux = linuxPackages.kernel;
>       };
>
> then it does work.
>
> I couldn't for the life of me understand why copying what is essentially
> the exact definitions of linuxPackages_4_4 and linuxPackages into my
> packageOverrides caused it to work.  The whole point of the
> packageOverride mechanism is to invoke late-binding so that I don't have
> to override long chains.
>
> I traced the issue to the following strange set of definitions:
>
> all-packages.nix begins with something like this
>
> { ... }:
> self: pkgs:
>
> with pkgs;
>
> { ... }
>
> It is a function of three arguments, (1) a set of parameters, (2) a
> binding for self, (3) a binding for pkgs, and the with pkgs; bring all
> the definitions from pkgs into scope.
>
> This is called from top-level/default.nix with the following
> expression:
>
>         allPackages = self: super:
>           let res = import ./all-packages.nix allPackagesArgs res self;
>           in res;
>
> So allPackageArgs contains the parameters, self gets bound to res, and
> pkgs get bound to self.
>
> The upshot of this is that within all-packages.nix self (which is bound
> to res) is the result of only evaluating all-packanges *with no
> overrides* while pkgs (which is bound to self) ends up late-bound and is
> the set of packges *with all overrides*
>
> So when linux and linuxPackages get bound using self in all-packages:
>
>     # The current default kernel / kernel modules.
>     linuxPackages = self.linuxPackages_4_4;
>     linux = self.linuxPackages.kernel;
>
> The use of self here (and throughout the linuxPackage definitions) means
> that we are making reference to the *unoverridden package set*.  This is
> why my packageOverrides of linux_4_4 did nothing, because the references
> to linux_4_4 inn all-packages.nix are prefixed with "self." which means
> it always gets the unoverriden packages.
>
> Is this really the desired behaviour?  I think that all-packages.nix is
> full of many questionable uses of the "self." prefix.  I suspect that
> people don't really understand that "self." means "give me the
> unoverriden version of packages".  I think renaming "self" in
> all-packages.nix to "unoverridenPackages" would be a better name.
>
> --
> Russell O'Connor                                      <http://r6.ca/>
> ``All talk about `theft,''' the general counsel of the American Graphophone
> Company wrote, ``is the merest claptrap, for there exists no property in
> ideas musical, literary or artistic, except as defined by statute.''
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