Regression in builtins.pathExists

[lucasew]

Describe the bug

After Nix 2.13.3 something happened and broke builtins.pathExists behaviour.

Steps To Reproduce

1. touch /tmp/test
2. nix repl
3. builtins.pathExists /tmp/test/.
   It will return true, should be false.

Expected behavior
It should return false.

nix-env --version output
nix-env (Nix) 2.17.0

Additional context
Nix 2.13.3 (tested on /nix/store/nd8dpdgpjkh3g3vvcjx9qdw7mjzz0l90-nix-2.13.3/bin/nix) doesn't have this issue.

This bug breaks impure overlays in nixpkgs. Relevant part of the code: https://github.com/NixOS/nixpkgs/blob/d28fdbe9742c680ec410bd70bf2962b90a374d36/pkgs/top-level/impure.nix#L40C1-L41C1

Priorities

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[lucasew]

[iFreilicht]

From the linked commit I assume that this issue does not exist in 2.15.2?

[lucasew]

From the linked commit I assume that this issue does not exist in 2.15.2?

Yes. 2.13.x was the version I was using before I bumped nixpkgs yesterday and I tried pinning to 2.15.2 that also doesn't have the issue.

[infinisil]

Bisecting (with some good guessing) tracks this down to 94812cc from #8172

[infinisil]

Note that this only changed behavior when passing strings to pathExists, so e.g. builtins.pathExists "/some/file/" now returns true when it returned false before. In comparison builtins.pathExists /some/file/ also returned true before.

This should definitely be fixed somehow.

[solson]

This issue was closed, but it is IMO still broken after #8869 because it only checks for trailing /, and doesn't handle cases like /.. As a consequence, Nixpkgs overlays are still broken because of this line: https://github.com/NixOS/nixpkgs/blob/9ace7896297b51fee5ad34c1977bec1e6541c089/pkgs/top-level/impure.nix#L40

At this point it's probably better to focus on NixOS/nixpkgs#249165, but I thought it worth commenting here because Nix is the cause of the regression, not Nixpkgs.