workflows/editorconfig: drop and move to treefmt

We already have treefmt running for nixfmt, so it's easy to just add
another formatter to it. This gives a much better UX, because all
formatting errors are reported through the same channel.

It also saves us one CI job, which takes most of the time to just set up
the machine, clone the repo and download Nix - while doing a minimum of
actual work.

Total execution time for treefmt is ~10% slower:
- 38s only nixfmt
- 43s nixfmt + editorconfig-checker

.github/workflows/check-format.yml

@@ -1,7 +1,4 @@
-# NOTE: Formatting with the RFC-style nixfmt command is not yet stable.
-# See https://github.com/NixOS/rfcs/pull/166.
-
-name: Check that Nix files are formatted
+name: Check that files are formatted
 
 on:
   pull_request_target:
@@ -14,7 +11,7 @@ jobs:
     uses: ./.github/workflows/get-merge-commit.yml
 
   nixos:
-    name: nixfmt-check
+    name: fmt-check
     runs-on: ubuntu-24.04
     needs: get-merge-commit
     if: needs.get-merge-commit.outputs.mergedSha
@@ -27,13 +24,13 @@ jobs:
         with:
           extra_nix_config: sandbox = true
 
-      - name: Check that Nix files are formatted
+      - name: Check that files are formatted
         run: |
           # Note that it's fine to run this on untrusted code because:
           # - There's no secrets accessible here
           # - The build is sandboxed
           if ! nix-build ci -A fmt.check; then
-            echo "Some Nix files are not properly formatted"
+            echo "Some files are not properly formatted"
             echo "Please format them by going to the Nixpkgs root directory and running one of:"
             echo "  nix-shell --run treefmt"
             echo "  nix develop --command treefmt"

.github/workflows/editorconfig-v2.yml

@@ -1,52 +0,0 @@
-name: "Checking EditorConfig v2"
-
-on:
-  pull_request_target:
-
-permissions: {}
-
-jobs:
-  get-merge-commit:
-    uses: ./.github/workflows/get-merge-commit.yml
-
-  tests:
-    name: editorconfig-check
-    runs-on: ubuntu-24.04
-    needs: get-merge-commit
-    if: "needs.get-merge-commit.outputs.mergedSha && !contains(github.event.pull_request.title, '[skip treewide]')"
-    steps:
-      - name: Get list of changed files from PR
-        env:
-          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-        run: |
-          gh api \
-            repos/${{ github.repository }}/pulls/${{ github.event.number }}/files --paginate \
-            | jq '.[] | select(.status != "removed") | .filename' \
-            > "$HOME/changed_files"
-
-      - name: print list of changed files
-        run: |
-          cat "$HOME/changed_files"
-
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
-        with:
-          ref: ${{ needs.get-merge-commit.outputs.mergedSha }}
-
-      - name: Get Nixpkgs revision for editorconfig-checker
-        run: |
-          # Pin to a commit from nixpkgs-unstable to avoid building from e.g. staging.
-          # This should not be a URL, because it would allow PRs to run arbitrary code in CI!
-          rev=$(jq -r .rev ci/pinned-nixpkgs.json)
-          echo "url=https://github.com/NixOS/nixpkgs/archive/$rev.tar.gz" >> "$GITHUB_ENV"
-
-      - uses: cachix/install-nix-action@526118121621777ccd86f79b04685a9319637641 # v31
-        with:
-          nix_path: nixpkgs=${{ env.url }}
-
-      - name: Checking EditorConfig
-        run: |
-          < "$HOME/changed_files" nix-shell -p editorconfig-checker --run 'xargs -r editorconfig-checker -disable-indent-size'
-
-      - if: ${{ failure() }}
-        run: |
-          echo "::error :: Hey! It looks like your changes don't follow our editorconfig settings. Read https://editorconfig.org/#download to configure your editor so you never see this error again."

ci/OWNERS

@@ -16,7 +16,7 @@
 # CI
 /.github/*_TEMPLATE*                    @SigmaSquadron
 /.github/workflows                      @NixOS/Security @Mic92 @zowoq @infinisil @azuwis @wolfgangwalther
-/.github/workflows/check-nix-format.yml @infinisil @wolfgangwalther
+/.github/workflows/check-format.yml     @infinisil @wolfgangwalther
 /.github/workflows/codeowners-v2.yml    @infinisil @wolfgangwalther
 /.github/workflows/nixpkgs-vet.yml      @infinisil @philiptaron @wolfgangwalther
 /ci                                     @infinisil @philiptaron @NixOS/Security @wolfgangwalther

ci/default.nix

@@ -48,6 +48,13 @@ let
         # the default formatter for Nix code.
         # See https://github.com/NixOS/nixfmt
         programs.nixfmt.enable = true;
+
+        settings.formatter.editorconfig-checker = {
+          command = "${pkgs.lib.getExe pkgs.editorconfig-checker}";
+          options = [ "-disable-indent-size" ];
+          includes = [ "*" ];
+          priority = 1;
+        };
       };
       fs = pkgs.lib.fileset;
       nixFilesSrc = fs.toSource {