lib/types: change pathInStore to allow leading period

[jfly]

As of nix v2.21.0:

Store paths are allowed to start with .

I'm not entirely sure what range of versions of nix we try to stay compatible with over here in nixpkgs. That said, I don't think particular change would cause issues for people using a version of nix that doesn't support leading periods.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 25.05 Release Notes (or backporting 24.11 and 25.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

---

Add a 👍 reaction to pull requests you find important.

[infinisil]

What's the motivation for this? And ping @ncfavier who introduced the type in #237259.

[ncfavier]

I assume what the changelog means is that paths like /nix/store/<hash>-.foo are now allowed. This obviously doesn't make a difference here.

[infinisil]

Although I'm just realising, the PR isn't changing whether a . is after /nix/store/<hash>-, but rather whether it's allowed after /nix/store/, as can be seen from the test that had to be changed, and that seems wrong. types.pathInStore doesn't look like it ever disallowed the paths that are newly allowed in Nix, so I don't think any change is necessary.

[roberth]

We already have:

nix-repl> lib.types.pathInStore.check "/nix/store/foo-.bashrc"
true

So leading periods are already accepted, and it seems we can close this particular PR.

---

However,

types.pathInStore
A path that is contained in the Nix store. This can be a top-level store
path like pkgs.hello or a descendant like "${pkgs.hello}/bin/hello".

This should not include /nix/store/. or /nix/store/... The exclusion of .links is ok, because that location is an implementation detail that should never be accessed by the evaluator, and not even by user generated config files.

Arguably /nix/store/a/.. should also be rejected, but that's not currently the case.

[jfly]

Urg, sorry. Now realizing that this PR made no sense, sorry for the noise.