In Git repository, only first file is formatted when passing multiple file paths

[evolutics]

Thanks for your work on treefmt.

Describe the bug

When running treefmt-nix with a list of files to format, only the first file is considered while any remaining files are ignored. This only happens in a Git repository.

It works when passing --walk filesystem as an option.

To Reproduce

Steps to reproduce the behavior:

1. Ensure you are in a Git repository.

2. Set up treefmt-nix with these (intentionally unformatted) files:

   • flake.nix with a default app to run the treefmt-nix wrapper:

     {
       inputs.treefmt-nix.url = "github:numtide/treefmt-nix";
     
       outputs = {
         self,
         nixpkgs,
         systems,
         treefmt-nix
       }: let
         eachSystem = f: nixpkgs.lib.genAttrs (import systems) (system: f nixpkgs.legacyPackages.${system});
         treefmtEval = eachSystem (pkgs: treefmt-nix.lib.evalModule pkgs ./treefmt.nix);
       in {
         formatter = eachSystem (pkgs: treefmtEval.${pkgs.system}.config.build.wrapper);
     
         apps = eachSystem (pkgs: {
           default = {
             program = "${treefmtEval.${pkgs.system}.config.build.wrapper}/bin/treefmt";
             type = "app";
           };
         });
       };
     }

   • treefmt.nix:

     {pkgs, ...}:
     {
       projectRootFile = "flake.nix";
       programs.alejandra.enable = true;
     }

3. Run treefmt-nix against the Nix files with

   $ git add .
   
   $ nix run . -- flake.nix treefmt.nix
   …
   traversed 1 files
   emitted 1 files for processing
   formatted 1 files (1 changed) in 11ms

Now only flake.nix is formatted but treefmt.nix is ignored.

Expected behavior

Both files should be formatted.

System information

Ubuntu 24.04.1 LTS with Nix 2.24.9.

flake.lock:

{
  "nodes": {
    "nixpkgs": {
      "locked": {
        "lastModified": 1729980323,
        "narHash": "sha256-eWPRZAlhf446bKSmzw6x7RWEE4IuZgAp8NW3eXZwRAY=",
        "owner": "NixOS",
        "repo": "nixpkgs",
        "rev": "86e78d3d2084ff87688da662cf78c2af085d8e73",
        "type": "github"
      },
      "original": {
        "id": "nixpkgs",
        "type": "indirect"
      }
    },
    "nixpkgs_2": {
      "locked": {
        "lastModified": 1726871744,
        "narHash": "sha256-V5LpfdHyQkUF7RfOaDPrZDP+oqz88lTJrMT1+stXNwo=",
        "owner": "nixos",
        "repo": "nixpkgs",
        "rev": "a1d92660c6b3b7c26fb883500a80ea9d33321be2",
        "type": "github"
      },
      "original": {
        "owner": "nixos",
        "ref": "nixpkgs-unstable",
        "repo": "nixpkgs",
        "type": "github"
      }
    },
    "root": {
      "inputs": {
        "nixpkgs": "nixpkgs",
        "systems": "systems",
        "treefmt-nix": "treefmt-nix"
      }
    },
    "systems": {
      "locked": {
        "lastModified": 1681028828,
        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
        "owner": "nix-systems",
        "repo": "default",
        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
        "type": "github"
      },
      "original": {
        "id": "systems",
        "type": "indirect"
      }
    },
    "treefmt-nix": {
      "inputs": {
        "nixpkgs": "nixpkgs_2"
      },
      "locked": {
        "lastModified": 1729613947,
        "narHash": "sha256-XGOvuIPW1XRfPgHtGYXd5MAmJzZtOuwlfKDgxX5KT3s=",
        "owner": "numtide",
        "repo": "treefmt-nix",
        "rev": "aac86347fb5063960eccb19493e0cadcdb4205ca",
        "type": "github"
      },
      "original": {
        "owner": "numtide",
        "repo": "treefmt-nix",
        "type": "github"
      }
    }
  },
  "root": "root",
  "version": 7
}

Additional context

As a workaround, run

nix run . -- --walk filesystem flake.nix treefmt.nix

[brianmcgee]

Path handling has been improved recently on main numtide/treefmt#438

I am hoping to get a release cut in the next week or so.