Add support for post-merge hooks

pre_commit/commands/hook_impl.py

@@ -76,6 +76,7 @@ def _ns(
         remote_url: Optional[str] = None,
         commit_msg_filename: Optional[str] = None,
         checkout_type: Optional[str] = None,
+        is_squash_merge: Optional[str] = None,
 ) -> argparse.Namespace:
     return argparse.Namespace(
         color=color,
@@ -88,6 +89,7 @@ def _ns(
         commit_msg_filename=commit_msg_filename,
         all_files=all_files,
         checkout_type=checkout_type,
+        is_squash_merge=is_squash_merge,
         files=(),
         hook=None,
         verbose=False,
@@ -158,6 +160,7 @@ def _pre_push_ns(
     'post-commit': 0,
     'pre-commit': 0,
     'pre-merge-commit': 0,
+    'post-merge': 1,
     'pre-push': 2,
 }
 
@@ -199,6 +202,8 @@ def _run_ns(
             hook_type, color,
             from_ref=args[0], to_ref=args[1], checkout_type=args[2],
         )
+    elif hook_type == 'post-merge':
+        return _ns(hook_type, color, is_squash_merge=args[0])
     else:
         raise AssertionError(f'unexpected hook type: {hook_type}')
 

pre_commit/commands/run.py

@@ -245,7 +245,7 @@ def _compute_cols(hooks: Sequence[Hook]) -> int:
 
 def _all_filenames(args: argparse.Namespace) -> Collection[str]:
     # these hooks do not operate on files
-    if args.hook_stage in {'post-checkout', 'post-commit'}:
+    if args.hook_stage in {'post-checkout', 'post-commit', 'post-merge'}:
         return ()
     elif args.hook_stage in {'prepare-commit-msg', 'commit-msg'}:
         return (args.commit_msg_filename,)
@@ -379,6 +379,9 @@ def run(
     if args.checkout_type:
         environ['PRE_COMMIT_CHECKOUT_TYPE'] = args.checkout_type
 
+    if args.is_squash_merge:
+        environ['PRE_COMMIT_IS_SQUASH_MERGE'] = args.is_squash_merge
+
     # Set pre_commit flag
     environ['PRE_COMMIT'] = '1'
 

pre_commit/constants.py

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

pre_commit/main.py

@@ -67,8 +67,8 @@ def __call__(
 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', 'post-commit', 'post-checkout',
+            'pre-commit', 'pre-merge-commit', 'pre-push', 'prepare-commit-msg',
+            'commit-msg', 'post-commit', 'post-checkout', 'post-merge',
         ),
         action=AppendReplaceDefault,
         default=['pre-commit'],
@@ -136,6 +136,13 @@ def _add_run_options(parser: argparse.ArgumentParser) -> None:
             'file from the index, flag=0).'
         ),
     )
+    parser.add_argument(
+        '--is-squash-merge',
+        help=(
+            'During a post-merge hook, indicates whether the merge was a '
+            'squash merge'
+        ),
+    )
 
 
 def _adjust_args_and_chdir(args: argparse.Namespace) -> None:

testing/util.py

@@ -70,6 +70,7 @@ def run_opts(
         show_diff_on_failure=False,
         commit_msg_filename='',
         checkout_type='',
+        is_squash_merge='',
 ):
     # These are mutually exclusive
     assert not (all_files and files)
@@ -88,6 +89,7 @@ def run_opts(
         show_diff_on_failure=show_diff_on_failure,
         commit_msg_filename=commit_msg_filename,
         checkout_type=checkout_type,
+        is_squash_merge=is_squash_merge,
     )
 
 

tests/commands/hook_impl_test.py

@@ -97,6 +97,7 @@ def call(*_, **__):
         ('pre-push', ['branch_name', 'remote_name']),
         ('commit-msg', ['.git/COMMIT_EDITMSG']),
         ('post-commit', []),
+        ('post-merge', ['1']),
         ('post-checkout', ['old_head', 'new_head', '1']),
         # multiple choices for commit-editmsg
         ('prepare-commit-msg', ['.git/COMMIT_EDITMSG']),
@@ -157,6 +158,14 @@ def test_run_ns_post_commit():
     assert ns.color is True
 
 
+def test_run_ns_post_merge():
+    ns = hook_impl._run_ns('post-merge', True, ('1',), b'')
+    assert ns is not None
+    assert ns.hook_stage == 'post-merge'
+    assert ns.color is True
+    assert ns.is_squash_merge == '1'
+
+
 def test_run_ns_post_checkout():
     ns = hook_impl._run_ns('post-checkout', True, ('a', 'b', 'c'), b'')
     assert ns is not None

tests/commands/install_uninstall_test.py

@@ -759,6 +759,48 @@ def test_post_commit_integration(tempdir_factory, store):
         assert os.path.exists('post-commit.tmp')
 
 
+def test_post_merge_integration(tempdir_factory, store):
+    path = git_dir(tempdir_factory)
+    config = [
+        {
+            'repo': 'local',
+            'hooks': [{
+                'id': 'post-merge',
+                'name': 'Post merge',
+                'entry': 'touch post-merge.tmp',
+                'language': 'system',
+                'always_run': True,
+                'verbose': True,
+                'stages': ['post-merge'],
+            }],
+        },
+    ]
+    write_config(path, config)
+    with cwd(path):
+        #  create a simple diamond of commits for a non-trivial merge
+        open('init', 'a').close()
+        cmd_output('git', 'add', '.')
+        git_commit()
+
+        open('master', 'a').close()
+        cmd_output('git', 'add', '.')
+        git_commit()
+
+        cmd_output('git', 'checkout', '-b', 'branch', 'HEAD^')
+        open('branch', 'a').close()
+        cmd_output('git', 'add', '.')
+        git_commit()
+
+        cmd_output('git', 'checkout', 'master')
+        install(C.CONFIG_FILE, store, hook_types=['post-merge'])
+        retc, stdout, stderr = cmd_output_mocked_pre_commit_home(
+            'git', 'merge', 'branch',
+            tempdir_factory=tempdir_factory,
+        )
+        assert retc == 0
+        assert os.path.exists('post-merge.tmp')
+
+
 def test_post_checkout_integration(tempdir_factory, store):
     path = git_dir(tempdir_factory)
     config = [

tests/commands/run_test.py

@@ -494,6 +494,15 @@ def test_all_push_options_ok(cap_out, store, repo_with_passing_hook):
     assert b'Specify both --from-ref and --to-ref.' not in printed
 
 
+def test_is_squash_merge(cap_out, store, repo_with_passing_hook):
+    args = run_opts(is_squash_merge='1')
+    environ: MutableMapping[str, str] = {}
+    ret, printed = _do_run(
+        cap_out, store, repo_with_passing_hook, args, environ,
+    )
+    assert environ['PRE_COMMIT_IS_SQUASH_MERGE'] == '1'
+
+
 def test_checkout_type(cap_out, store, repo_with_passing_hook):
     args = run_opts(from_ref='', to_ref='', checkout_type='1')
     environ: MutableMapping[str, str] = {}

tests/repository_test.py

@@ -953,7 +953,7 @@ def test_manifest_hooks(tempdir_factory, store):
         require_serial=False,
         stages=(
             'commit', 'merge-commit', 'prepare-commit-msg', 'commit-msg',
-            'post-commit', 'manual', 'post-checkout', 'push',
+            'post-commit', 'manual', 'post-checkout', 'push', 'post-merge',
         ),
         types=['file'],
         types_or=[],