treewide: add checks for nix.enable
#1332
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This was added to Nixpkgs in eb8b70c020e6693b29634660fa173d7f14f882eb.
This was added to Nixpkgs in eb8b70c020e6693b29634660fa173d7f14f882eb.
When we’re not managing the Nix installation, these defaults aren’t used out of the box and won’t accurately represent the state of any unmanaged Nix or the desired Nix package, so reading the option defaults is a bug. This was previously a warning for `nix.package` and a silent failure for all the others. Now that all the problematic accesses in nix-darwin have been appropriately conditionalized, and since a throw gives a backtrace where a warning doesn’t, give throwing defaults to all the `nix.*` options that don’t reflect reality and that that modules shouldn’t be reading when `nix.enable` is off. I’m not in love with the implementation strategy here… ideally we’d think of something better than this and then upstream it to NixOS. `nix.nrBuildUsers` growing a fake default that is never used is particularly unfortunate. But this should hopefully catch mistakes in module code reasonably reliably.
When `nix.enable` is off, we don’t necessarily have an active Nix installation, so there won’t necessarily be an active `/nix/var/nix/gcroots` directory to link things into. NixOS just skips this unconditionally when `nix.enable` is off, but that doesn’t work well with a context in which we usually expect `nix.enable` to be coupled with an unmanaged system installation of Nix.
Enzime
approved these changes
Feb 14, 2025
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Things that expect a managed Nix installation should have a corresponding assertion so that we don’t incorrectly use the default
nix.packagewhen the user has opted out of Nix management or otherwise interfere with use of an unmanaged system Nix. NixOS had some of these checks already but I didn’t catch them when backporting the functionality in the initial PR; others are in modules only present in nix-darwin, or else should probably be upstreamed to NixOS at some point. Also fix some miscellaneous other bugs where we were incorrectly using the managed defaults or assuming the guaranteed presence of an active Nix installation even whennix.enablewas turned off. See commit messages for more details.Note: This work was funded by Determinate Systems.