Add post-checkout

pre_commit/commands/hook_impl.py

@@ -74,6 +74,7 @@ def _ns(
         remote_name: Optional[str] = None,
         remote_url: Optional[str] = None,
         commit_msg_filename: Optional[str] = None,
+        checkout_type: Optional[str] = None,
 ) -> argparse.Namespace:
     return argparse.Namespace(
         color=color,
@@ -84,6 +85,7 @@ def _ns(
         remote_url=remote_url,
         commit_msg_filename=commit_msg_filename,
         all_files=all_files,
+        checkout_type=checkout_type,
         files=(),
         hook=None,
         verbose=False,
@@ -157,6 +159,11 @@ def _run_ns(
         return _ns(hook_type, color, commit_msg_filename=args[0])
     elif hook_type in {'pre-merge-commit', 'pre-commit'}:
         return _ns(hook_type, color)
+    elif hook_type == 'post-checkout':
+        return _ns(
+            hook_type, color, source=args[0], origin=args[1],
+            checkout_type=args[2],
+        )
     else:
         raise AssertionError(f'unexpected hook type: {hook_type}')
 

pre_commit/commands/run.py

@@ -316,6 +316,9 @@ def run(
         environ['PRE_COMMIT_REMOTE_NAME'] = args.remote_name
         environ['PRE_COMMIT_REMOTE_URL'] = args.remote_url
 
+    if args.checkout_type:
+        environ['PRE_COMMIT_CHECKOUT_TYPE'] = args.checkout_type
+
     with contextlib.ExitStack() as exit_stack:
         if stash:
             exit_stack.enter_context(staged_files_only(store.directory))

pre_commit/constants.py

@@ -18,7 +18,7 @@ VERSION = importlib_metadata.version('pre_commit')
 # `manual` is not invoked by any installed git hook.  See #719
 STAGES = (
     'commit', 'merge-commit', 'prepare-commit-msg', 'commit-msg', 'manual',
-    'push',
+    'post-checkout', 'push',
 )
 
 DEFAULT = 'default'

pre_commit/main.py

@@ -79,7 +79,7 @@ def _add_hook_type_option(parser: argparse.ArgumentParser) -> None:
     parser.add_argument(
         '-t', '--hook-type', choices=(
             'pre-commit', 'pre-merge-commit', 'pre-push',
-            'prepare-commit-msg', 'commit-msg',
+            'prepare-commit-msg', 'commit-msg', 'post-checkout',
         ),
         action=AppendReplaceDefault,
         default=['pre-commit'],
@@ -92,11 +92,17 @@ def _add_run_options(parser: argparse.ArgumentParser) -> None:
     parser.add_argument('--verbose', '-v', action='store_true', default=False)
     parser.add_argument(
         '--origin', '-o',
-        help="The origin branch's commit_id when using `git push`.",
+        help=(
+            "The origin branch's commit_id when using `git push`.  "
+            'The ref of the previous HEAD when using `git checkout`.'
+        ),
     )
     parser.add_argument(
         '--source', '-s',
-        help="The remote branch's commit_id when using `git push`.",
+        help=(
+            "The remote branch's commit_id when using `git push`.  "
+            'The ref of the new HEAD when using `git checkout`.'
+        ),
     )
     parser.add_argument(
         '--commit-msg-filename',
@@ -123,6 +129,14 @@ def _add_run_options(parser: argparse.ArgumentParser) -> None:
         '--files', nargs='*', default=[],
         help='Specific filenames to run hooks on.',
     )
+    parser.add_argument(
+        '--checkout-type',
+        help=(
+            'Indicates whether the checkout was a branch checkout '
+            '(changing branches, flag=1) or a file checkout (retrieving a '
+            'file from the index, flag=0).'
+        ),
+    )
 
 
 def _adjust_args_and_chdir(args: argparse.Namespace) -> None: