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

[roconnor at theorem.ca]

I haven't heard back from Nicolas yet.

Perhaps I should put together a PR that removes the instances of self that 
I think are wrong so that we can discuss the issue.

On Sun, 8 May 2016, Daniel Peebles wrote:

> 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.''
>       _______________________________________________
>       nix-dev mailing list
>       nix-dev at lists.science.uu.nl
>       http://lists.science.uu.nl/mailman/listinfo/nix-dev
> 
> 
> 
>

-- 
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.''