Add check-yaml-filename-extension hook

pre_commit_hooks/check_yaml_filename_extension.py

@@ -0,0 +1,29 @@
+from __future__ import annotations
+
+import argparse
+import os
+from typing import Sequence
+
+from pre_commit_hooks.util import cmd_output
+
+
+def main(argv: Sequence[str] | None = None) -> int:
+    parser = argparse.ArgumentParser()
+    parser.add_argument('--extension', choices=['yaml', 'yml'], default='yaml')
+    parser.add_argument('filenames', nargs='*', help='Filenames to check.')
+
+    args = parser.parse_args(argv)
+    extension = f'.{args.extension}'
+
+    retval = 0
+    for filename in args.filenames:
+        if not filename.endswith(extension):
+            new_filename = f'{os.path.splitext(filename)[0]}{extension}'
+            cmd_output('git', 'mv', filename, new_filename)
+            retval = 1
+
+    return retval
+
+
+if __name__ == '__main__':
+    raise SystemExit(main())