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List:       nix-dev
Subject:    Re: [Nix-dev] all-packages.nix and the unoverridable self.
From:       roconnor () theorem ! ca
Date:       2016-05-08 17:44:25
Message-ID: alpine.LRH.2.11.1605081043020.541 () turing ! theorem ! ca
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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@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@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.''



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