2.16 regression: invoking nix-shell -p: overlays.nix should be a file

[SFrijters]

Describe the bug

$ nix-shell --packages jq
error:
       … <borked>

         at «none»:0: (source not available)

       … while evaluating a branch condition

         at /nix/store/8arv4302k0fi1ix92gipxwggzycvyzmj-source/lib/trivial.nix:386:27:

          385|   */
          386|   throwIfNot = cond: msg: if cond then x: x else throw msg;
             |                           ^
          387|

       (stack trace truncated; use '--show-trace' to show the full trace)

       error: /home/frijters/.config/nixpkgs/overlays.nix should be a file
$ nix --version
nix (Nix) 2.16.0

It works fine on 2.15.1.

My overlays.nix file is a symlink; I also tried having overlays.nix be a regular file while the nixpkgs directory is a symlink: same error.

Steps To Reproduce

See above.

Expected behavior

nix-shell should not care about how I organize my overlays.

nix-env --version output

nix-env (Nix) 2.16.0

Additional context

Add any other context about the problem here.

Priorities

Add 👍 to issues you find important.

[igsha]

I have the same error. Possible fix: I split my overlays.nix into self: super: functions and place them into ~/.config/nixpkgs/overlays/ directory.

[samuela]

I'm seeing the same error under slightly different conditions. In my case, I have a regular, non-symlink /home/sam.ainsworth/.config/nixpkgs/overlays.nix file:

[
  # (final: prev: rec {
  #   python3 = prev.python3.override { packageOverrides = final: prev: { jaxlib = prev.jaxlib-bin; }; };
  #   python3Packages = python3.pkgs;
  # })
]

but nix 2.16.1 is not a happy camper:

error:
       … while evaluating a branch condition

         at /nix/store/jn1i9jic6cga9sbyfsqdiyci6w1nk9i6-nixpkgs/nixpkgs/lib/trivial.nix:386:27:

          385|   */
          386|   throwIfNot = cond: msg: if cond then x: x else throw msg;
             |                           ^
          387|

       … while calling the 'isList' builtin

         at /nix/store/jn1i9jic6cga9sbyfsqdiyci6w1nk9i6-nixpkgs/nixpkgs/pkgs/top-level/default.nix:55:17:

           54|   checked =
           55|     throwIfNot (lib.isList overlays) "The overlays argument to nixpkgs must be a list."
             |                 ^
           56|     lib.foldr (x: throwIfNot (lib.isFunction x) "All overlays passed to nixpkgs must be functions.") (r: r) overlays

       (stack trace truncated; use '--show-trace' to show the full trace)

       error: /home/sam.ainsworth/.config/nixpkgs/overlays.nix should be a file

removing overlays.nix resolved the issue for me

[dgchurchill]

Looks like isDir homeOverlaysFile here must now be returning true even if overlays.nix is a file.

isDir is defined as path: builtins.pathExists (path + "/.")

Nothing seems to have changed recently. The only thing I can see is SourcePath pathExists being introduced recently which is

    bool pathExists() const
    { return nix::pathExists(path.abs()); }

I don't know how builtins is constructed though, and whether this is even relevant. The path.abs hints that it might be though, and how it could interact with path + "/."

[miuirussia]

Replacing the isDir function with a more reasonable one fixed the problem:

isDir = path: builtins.readFileType path == "directory";

https://github.com/miuirussia/nixpkgs/blob/48516fdd5b7ea910bf82b056030eea8960791599/pkgs/top-level/impure.nix#L40C7-L40C63

[solson]

Possibly related (and just now fixed): #8838

[SFrijters]

I patched nix 2.17 with #8838 and it does not solve this particular issue for me.

[solson]

Yeah, I noticed later that #8869 was insufficient for this issue (and left some comments on the PR and issue). There's a PR currently open in nixpkgs that will work around this regression in nix: NixOS/nixpkgs#249165