ci: tag-maintainers extract maintainers in a separate script

Make it easier to test the workflow by moving logic out into separate
script.

.github/workflows/tag-maintainers.yml

@@ -67,52 +67,9 @@ jobs:
           PR_AUTHOR: "${{ github.event.pull_request.user.login }}"
           CHANGED_FILES: '${{ steps.changed-files.outputs.changed_files }}'
         run: |
-          if [[ -z "$CHANGED_FILES" ]]; then
-            echo "No plugin files changed. No maintainers to tag."
-            echo "maintainers=" >> "$GITHUB_OUTPUT"
-            exit 0
-          fi
-
-          echo "Evaluating nixvim meta system for all maintainers..."
-          # Get a JSON object mapping plugin paths to maintainer data.
-          ALL_MAINTAINERS=$(nix eval --impure --expr "
-            let
-              nixvim = import ./.;
-              lib = nixvim.inputs.nixpkgs.lib.extend nixvim.lib.overlay;
-              emptyConfig = lib.nixvim.evalNixvim {
-                modules = [ { _module.check = false; } ];
-                extraSpecialArgs = { pkgs = null; };
-              };
-              inherit (emptyConfig.config.meta) maintainers;
-            in
-              maintainers
-          " --json 2>/dev/null || echo "{}")
-
-          echo "Finding maintainers for changed files..."
-          FOUND_MAINTAINERS=$(
-            echo "$CHANGED_FILES" | while IFS= read -r FILE; do
-              [[ -z "$FILE" ]] && continue
-              PLUGIN_DIR=$(dirname "$FILE")
-
-              # Use jq to find maintainers whose path key ends with the plugin directory.
-              echo "$ALL_MAINTAINERS" | jq -r --arg plugindir "$PLUGIN_DIR" '
-                to_entries[] |
-                select(.key | endswith($plugindir)) |
-                .value[] |
-                select(has("github")) |
-                .github
-              ' 2>/dev/null
-            done
-          )
-
-          # De-duplicate the list, remove the PR author, and format as a space-separated string.
-          MAINTAINERS_LIST=$(echo "$FOUND_MAINTAINERS" | grep -v -w -F "$PR_AUTHOR" | sort -u | tr '\n' ' ' | sed 's/ *$//')
-
-          if [[ -z "$MAINTAINERS_LIST" ]]; then
-            echo "No maintainers found for changed files (or only the PR author is a maintainer)."
-          else
-            echo "Found maintainers to notify: $MAINTAINERS_LIST"
-          fi
+          MAINTAINERS_LIST=$(./ci/tag-maintainers/extract-maintainers.py \
+            --changed-files "$CHANGED_FILES" \
+            --pr-author "$PR_AUTHOR")
 
           echo "maintainers=$MAINTAINERS_LIST" >> "$GITHUB_OUTPUT"
 

ci/tag-maintainers/extract-maintainers.py

@@ -0,0 +1,116 @@
+#!/usr/bin/env python3
+"""
+Extract maintainers from changed plugin files.
+
+This script extracts the maintainer extraction logic from the tag-maintainers workflow
+for easier testing and validation.
+"""
+
+import argparse
+import json
+import subprocess
+import sys
+from typing import List
+
+
+def run_nix_eval(expr: str) -> str:
+    """Run a Nix evaluation expression and return the result."""
+    try:
+        result = subprocess.run(
+            ["nix", "eval", "--impure", "--json", "--expr", expr],
+            capture_output=True,
+            text=True,
+            check=True,
+        )
+        return result.stdout.strip()
+    except subprocess.CalledProcessError as e:
+        print(f"Error running Nix evaluation: {e}", file=sys.stderr)
+        print(f"Stderr: {e.stderr}", file=sys.stderr)
+        return "[]"
+
+
+def extract_maintainers(changed_files: List[str], pr_author: str) -> List[str]:
+    """Extract maintainers from changed plugin files."""
+    if not changed_files:
+        print("No plugin files changed. No maintainers to tag.", file=sys.stderr)
+        return []
+
+    print("Finding maintainers for changed files...", file=sys.stderr)
+
+    changed_files_nix = '[ ' + ' '.join(f'"{f}"' for f in changed_files) + ' ]'
+
+    nix_expr = f"""
+    let
+      nixvim = import ./.;
+      lib = nixvim.inputs.nixpkgs.lib;
+      emptyConfig = nixvim.lib.nixvim.evalNixvim {{
+        modules = [ {{ _module.check = false; }} ];
+        extraSpecialArgs.pkgs = null;
+      }};
+      inherit (emptyConfig.config.meta) maintainers;
+
+      changedFiles = {changed_files_nix};
+
+      # Find maintainers for files that match changed plugin directories
+      relevantMaintainers = lib.concatLists (
+        lib.mapAttrsToList (path: maintainerList:
+          let
+            matchingFiles = lib.filter (file:
+              lib.hasSuffix (dirOf file) path
+            ) changedFiles;
+          in
+            if matchingFiles != [] then maintainerList else []
+        ) maintainers
+      );
+
+      # Extract GitHub usernames
+      githubUsers = lib.concatMap (maintainer:
+        if maintainer ? github then [ maintainer.github ] else []
+      ) relevantMaintainers;
+
+    in
+      lib.unique githubUsers
+    """
+
+    result = run_nix_eval(nix_expr)
+
+    try:
+        maintainers = json.loads(result)
+    except json.JSONDecodeError:
+        print(f"Error parsing Nix evaluation result: {result}", file=sys.stderr)
+        return []
+
+    filtered_maintainers = [m for m in maintainers if m != pr_author]
+
+    if not filtered_maintainers:
+        print("No maintainers found for changed files (or only the PR author is a maintainer).", file=sys.stderr)
+        return []
+    else:
+        print(f"Found maintainers to notify: {' '.join(filtered_maintainers)}", file=sys.stderr)
+        return filtered_maintainers
+
+
+def main() -> None:
+    """Main function to handle command line arguments and run the extraction."""
+    parser = argparse.ArgumentParser(
+        description="Extract maintainers from changed plugin files"
+    )
+    parser.add_argument(
+        "--changed-files",
+        help="Newline-separated list of changed files",
+        default="",
+    )
+    parser.add_argument(
+        "--pr-author",
+        required=True,
+        help="GitHub username of the PR author",
+    )
+
+    args = parser.parse_args()
+    changed_files = [f.strip() for f in args.changed_files.split('\n') if f.strip()]
+    maintainers = extract_maintainers(changed_files, args.pr_author)
+    print(' '.join(maintainers))
+
+
+if __name__ == "__main__":
+    main()