nixpkgs module: Fix defaulting of localSystem and system
#40708
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My c6f7d43 made the mistake of not having enough defaults. Now both variables are default as the *explicit* value of the other, or a fallback. The fallback of `system` is the default of `localSystem.system`. The fallback of `localSystem` is not the other default (projected), as that would cause a cycle, but `{ system = builtins.currentTime; }` just as nixpkgs itself does it.
GrahamcOfBorg
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6.topic: nixos
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Also I'm super excited to test this, thanks!! (but not sure when I'll get to it... hopefully soon!) |
matthewbauer
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May 30, 2018
Ericson2314
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Sep 7, 2018
Take two of NixOS#40708 (4fe2898). That PR attempted to bidirectionally default `config.nixpkgs.system` and `config.nixpkgs.localSystem.system` to each be updated by the other. But this is not possible with the way the module system works. Divergence in certain cases in inevitable. This PR is more conservative and just has `system` default `localSystem` and `localSystem` make the final call as-is. This solves a number of issues. - `localSystem` completely overrides `system`, just like with nixpkgs proper. There is no need to specify `localSystem.system` to clobber the old system. - `config.nixpkgs.localSystem` is exactly what is passed to nixpkgs. No spooky steps. - `config.nixpkgs.localSystem` is elaborated just as nixpkgs would so that all attributes are available, not just the ones the user specified. The remaining issue is just that `config.nixpkgs.system` doesn't update based on `config.nixpkgs.localSystem.system`. It should never be referred to lest it is a bogus stale value because `config.nixpkgs.localSystem` overwrites it. Fixes NixOS#46320
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Motivation for this change
My c6f7d43 made the mistake of not
having enough defaults. Now both variables are default as the explicit
value of the other, or a fallback. The fallback of
systemis thedefault of
localSystem.system. The fallback oflocalSystemis notthe other default (projected), as that would cause a cycle, but
{ system = builtins.currentTime; }just as nixpkgs itself does it.Things done
build-use-sandboxinnix.confon non-NixOS)nix-shell -p nox --run "nox-review wip"./result/bin/)CC @ElvishJerricco