Parse frozen tag comment instead of pinned sha for rev

sync_pre_commit_deps.py

@@ -20,6 +20,23 @@
 
 _SEPS = ('==', '@')
 _RE_SEP = re.compile(rf'^(.+)({"|".join(_SEPS)})(.+)$')
+_RE_FROZEN = re.compile(r'#\s*frozen:\s*(\S+)')
+
+
+def _version(repo: ruamel.yaml.comments.CommentedMap) -> str:
+    tokens = repo.ca.items.get('rev') or ()
+    for token in tokens:
+        if token and (match := _RE_FROZEN.search(token.value)):
+            rev = match.group(1)
+            break
+    else:
+        rev = repo['rev']
+
+    # `mirrors-mypy` and various node revs have a 'v' prefix,
+    # so we have to strip that out to get the
+    # additional_dependency version.
+    return rev.removeprefix('v')
+
 
 _ARGUMENT_HELP_TEMPLATE = (
     'The `{}` argument to the YAML dumper. '
@@ -69,11 +86,7 @@ def main(argv: Sequence[str] | None = None) -> int:
         if repo['repo'] not in ('local', 'meta'):
             for hook in repo['hooks']:
                 if (dep := SUPPORTED.get(hook['id'])) is not None:
-                    # `mirrors-mypy` and various node revs have a 'v' prefix,
-                    # so we have to strip that out to get the
-                    # additional_dependency version.
-                    cleaned_rev = repo['rev'].removeprefix('v')
-                    versions[dep] = cleaned_rev
+                    versions[dep] = _version(repo)
 
     updated = []
     for repo in loaded['repos']:

tests/sync_pre_commit_deps_test.py

@@ -228,6 +228,37 @@ def test_main_writes_all(tmpdir):
     )
 
 
+def test_main_frozen_rev_uses_tag_not_sha(tmpdir):
+    cfg = tmpdir.join('.pre-commit-config.yaml')
+    cfg.write(
+        'repos:\n'
+        '-   repo: https://github.com/biomejs/pre-commit\n'
+        '    rev: 5bb716344fd6979d991634e7ece88f407e599ee0  # frozen: v2.5.4\n'
+        '    hooks:\n'
+        '    -   id: biome-check\n'
+        '-   repo: local\n'
+        '    hooks:\n'
+        '    -   id: biome-migrate\n'
+        '        additional_dependencies:\n'
+        '        -   "@biomejs/biome@2.4.15"\n',
+    )
+
+    assert main((str(cfg),))
+
+    assert cfg.read() == (
+        'repos:\n'
+        '-   repo: https://github.com/biomejs/pre-commit\n'
+        '    rev: 5bb716344fd6979d991634e7ece88f407e599ee0  # frozen: v2.5.4\n'
+        '    hooks:\n'
+        '    -   id: biome-check\n'
+        '-   repo: local\n'
+        '    hooks:\n'
+        '    -   id: biome-migrate\n'
+        '        additional_dependencies:\n'
+        '        -   "@biomejs/biome@2.5.4"\n'
+    )
+
+
 def test_main_no_dep_on_one_and_writes_other(tmpdir):
     cfg = tmpdir.join('.pre-commit-config.yaml')
     cfg.write(