support pre-merge-commit

pre_commit/constants.py

@@ -26,6 +26,9 @@
 VERSION = importlib_metadata.version('pre_commit')
 
 # `manual` is not invoked by any installed git hook.  See #719
-STAGES = ('commit', 'prepare-commit-msg', 'commit-msg', 'manual', 'push')
+STAGES = (
+    'commit', 'merge-commit', 'prepare-commit-msg', 'commit-msg', 'manual',
+    'push',
+)
 
 DEFAULT = 'default'

pre_commit/main.py

@@ -70,7 +70,8 @@ def __call__(self, parser, namespace, values, option_string=None):
 def _add_hook_type_option(parser):
     parser.add_argument(
         '-t', '--hook-type', choices=(
-            'pre-commit', 'pre-push', 'prepare-commit-msg', 'commit-msg',
+            'pre-commit', 'pre-merge-commit', 'pre-push',
+            'prepare-commit-msg', 'commit-msg',
         ),
         action=AppendReplaceDefault,
         default=['pre-commit'],

pre_commit/resources/hook-tmpl

@@ -163,6 +163,7 @@ def _opts(stdin):
     fns = {
         'prepare-commit-msg': lambda _: ('--commit-msg-filename', sys.argv[1]),
         'commit-msg': lambda _: ('--commit-msg-filename', sys.argv[1]),
+        'pre-merge-commit': lambda _: (),
         'pre-commit': lambda _: (),
         'pre-push': _pre_push,
     }

tests/commands/install_uninstall_test.py

@@ -742,6 +742,32 @@ def test_prepare_commit_msg_legacy(
         assert 'Signed off by: ' in f.read()
 
 
+def test_pre_merge_commit_integration(tempdir_factory, store):
+    expected = re.compile(
+        r'^\[INFO\] Initializing environment for .+\n'
+        r'Bash hook\.+Passed\n'
+        r"Merge made by the 'recursive' strategy.\n"
+        r' foo \| 0\n'
+        r' 1 file changed, 0 insertions\(\+\), 0 deletions\(-\)\n'
+        r' create mode 100644 foo\n$',
+    )
+
+    path = make_consuming_repo(tempdir_factory, 'script_hooks_repo')
+    with cwd(path):
+        ret = install(C.CONFIG_FILE, store, hook_types=['pre-merge-commit'])
+        assert ret == 0
+
+        cmd_output('git', 'checkout', 'master', '-b', 'feature')
+        _get_commit_output(tempdir_factory)
+        cmd_output('git', 'checkout', 'master')
+        ret, output, _ = cmd_output_mocked_pre_commit_home(
+            'git', 'merge', '--no-ff', '--no-edit', 'feature',
+            tempdir_factory=tempdir_factory,
+        )
+        assert ret == 0
+        assert expected.match(output)
+
+
 def test_install_disallow_missing_config(tempdir_factory, store):
     path = make_consuming_repo(tempdir_factory, 'script_hooks_repo')
     with cwd(path):

tests/repository_test.py

@@ -895,7 +895,8 @@ def test_manifest_hooks(tempdir_factory, store):
         pass_filenames=True,
         require_serial=False,
         stages=(
-            'commit', 'prepare-commit-msg', 'commit-msg', 'manual', 'push',
+            'commit', 'merge-commit', 'prepare-commit-msg', 'commit-msg',
+            'manual', 'push',
         ),
         types=['file'],
         verbose=False,