fix hooks firing during staged_files_only

pre_commit/commands/run.py

@@ -324,6 +324,12 @@ def run(
             f'`--hook-stage {args.hook_stage}`',
         )
         return 1
+    # prevent recursive post-checkout hooks (#1418)
+    if (
+            args.hook_stage == 'post-checkout' and
+            environ.get('_PRE_COMMIT_SKIP_POST_CHECKOUT')
+    ):
+        return 0
 
     # Expose from-ref / to-ref as environment variables for hooks to consume
     if args.from_ref and args.to_ref:

pre_commit/staged_files_only.py

@@ -56,8 +56,10 @@ def _unstaged_changes_cleared(patch_dir: str) -> Generator[None, None, None]:
         with open(patch_filename, 'wb') as patch_file:
             patch_file.write(diff_stdout_binary)
 
-        # Clear the working directory of unstaged changes
-        cmd_output_b('git', 'checkout', '--', '.')
+        # prevent recursive post-checkout hooks (#1418)
+        no_checkout_env = dict(os.environ, _PRE_COMMIT_SKIP_POST_CHECKOUT='1')
+        cmd_output_b('git', 'checkout', '--', '.', env=no_checkout_env)
+
         try:
             yield
         finally:
@@ -72,8 +74,9 @@ def _unstaged_changes_cleared(patch_dir: str) -> Generator[None, None, None]:
                 # We failed to apply the patch, presumably due to fixes made
                 # by hooks.
                 # Roll back the changes made by hooks.
-                cmd_output_b('git', 'checkout', '--', '.')
+                cmd_output_b('git', 'checkout', '--', '.', env=no_checkout_env)
                 _git_apply(patch_filename)
+
             logger.info(f'Restored changes from {patch_filename}.')
     else:
         # There weren't any staged files so we don't need to do anything

testing/util.py

@@ -103,10 +103,12 @@ def cwd(path):
         os.chdir(original_cwd)
 
 
-def git_commit(*args, fn=cmd_output, msg='commit!', **kwargs):
+def git_commit(*args, fn=cmd_output, msg='commit!', all_files=True, **kwargs):
     kwargs.setdefault('stderr', subprocess.STDOUT)
 
-    cmd = ('git', 'commit', '--allow-empty', '--no-gpg-sign', '-a') + args
+    cmd = ('git', 'commit', '--allow-empty', '--no-gpg-sign', *args)
+    if all_files:  # allow skipping `-a` with `all_files=False`
+        cmd += ('-a',)
     if msg is not None:  # allow skipping `-m` with `msg=None`
         cmd += ('-m', msg)
     ret, out, _ = fn(*cmd, **kwargs)

tests/commands/install_uninstall_test.py

@@ -789,6 +789,37 @@ def test_post_checkout_integration(tempdir_factory, store):
         assert 'some_file' not in stderr
 
 
+def test_skips_post_checkout_unstaged_changes(tempdir_factory, store):
+    path = git_dir(tempdir_factory)
+    config = {
+        'repo': 'local',
+        'hooks': [{
+            'id': 'fail',
+            'name': 'fail',
+            'entry': 'fail',
+            'language': 'fail',
+            'always_run': True,
+            'stages': ['post-checkout'],
+        }],
+    }
+    write_config(path, config)
+    with cwd(path):
+        cmd_output('git', 'add', '.')
+        _get_commit_output(tempdir_factory)
+
+        install(C.CONFIG_FILE, store, hook_types=['pre-commit'])
+        install(C.CONFIG_FILE, store, hook_types=['post-checkout'])
+
+        # make an unstaged change so staged_files_only fires
+        open('file', 'a').close()
+        cmd_output('git', 'add', 'file')
+        with open('file', 'w') as f:
+            f.write('unstaged changes')
+
+        retc, out = _get_commit_output(tempdir_factory, all_files=False)
+        assert retc == 0
+
+
 def test_prepare_commit_msg_integration_failing(
         failing_prepare_commit_msg_repo, tempdir_factory, store,
 ):

tests/commands/run_test.py

@@ -1022,3 +1022,9 @@ def test_args_hook_only(cap_out, store, repo_with_passing_hook):
         run_opts(hook='do_not_commit'),
     )
     assert b'identity-copy' not in printed
+
+
+def test_skipped_without_any_setup_for_post_checkout(in_git_dir, store):
+    environ = {'_PRE_COMMIT_SKIP_POST_CHECKOUT': '1'}
+    opts = run_opts(hook_stage='post-checkout')
+    assert run(C.CONFIG_FILE, store, opts, environ=environ) == 0