1 files changed, 90 insertions, 0 deletions
diff --git a/pre_commit/commands/gc.py b/pre_commit/commands/gc.py
new file mode 100644
index 0000000..7f6d311
--- /dev/null
+++ b/pre_commit/commands/gc.py
@@ -0,0 +1,90 @@
+import os.path
+from typing import Any
+from typing import Dict
+from typing import Set
+from typing import Tuple
+
+import pre_commit.constants as C
+from pre_commit import output
+from pre_commit.clientlib import InvalidConfigError
+from pre_commit.clientlib import InvalidManifestError
+from pre_commit.clientlib import load_config
+from pre_commit.clientlib import load_manifest
+from pre_commit.clientlib import LOCAL
+from pre_commit.clientlib import META
+from pre_commit.store import Store
+
+
+def _mark_used_repos(
+        store: Store,
+        all_repos: Dict[Tuple[str, str], str],
+        unused_repos: Set[Tuple[str, str]],
+        repo: Dict[str, Any],
+) -> None:
+    if repo['repo'] == META:
+        return
+    elif repo['repo'] == LOCAL:
+        for hook in repo['hooks']:
+            deps = hook.get('additional_dependencies')
+            unused_repos.discard((
+                store.db_repo_name(repo['repo'], deps), C.LOCAL_REPO_VERSION,
+            ))
+    else:
+        key = (repo['repo'], repo['rev'])
+        path = all_repos.get(key)
+        # can't inspect manifest if it isn't cloned
+        if path is None:
+            return
+
+        try:
+            manifest = load_manifest(os.path.join(path, C.MANIFEST_FILE))
+        except InvalidManifestError:
+            return
+        else:
+            unused_repos.discard(key)
+            by_id = {hook['id']: hook for hook in manifest}
+
+        for hook in repo['hooks']:
+            if hook['id'] not in by_id:
+                continue
+
+            deps = hook.get(
+                'additional_dependencies',
+                by_id[hook['id']]['additional_dependencies'],
+            )
+            unused_repos.discard((
+                store.db_repo_name(repo['repo'], deps), repo['rev'],
+            ))
+
+
+def _gc_repos(store: Store) -> int:
+    configs = store.select_all_configs()
+    repos = store.select_all_repos()
+
+    # delete config paths which do not exist
+    dead_configs = [p for p in configs if not os.path.exists(p)]
+    live_configs = [p for p in configs if os.path.exists(p)]
+
+    all_repos = {(repo, ref): path for repo, ref, path in repos}
+    unused_repos = set(all_repos)
+    for config_path in live_configs:
+        try:
+            config = load_config(config_path)
+        except InvalidConfigError:
+            dead_configs.append(config_path)
+            continue
+        else:
+            for repo in config['repos']:
+                _mark_used_repos(store, all_repos, unused_repos, repo)
+
+    store.delete_configs(dead_configs)
+    for db_repo_name, ref in unused_repos:
+        store.delete_repo(db_repo_name, ref, all_repos[(db_repo_name, ref)])
+    return len(unused_repos)
+
+
+def gc(store: Store) -> int:
+    with store.exclusive_lock():
+        repos_removed = _gc_repos(store)
+    output.write_line(f'{repos_removed} repo(s) removed.')
+    return 0