Adds support for prepare-commit-msg hooks

Adds a prepare-commit-msg hook stage which allows for hooks which add
dynamic suggested/placeholder text to commit messages that an author can
use as a starting point for writing a commit message

pre_commit/commands/run.py

@@ -190,7 +190,7 @@ def _compute_cols(hooks, verbose):
 def _all_filenames(args):
     if args.origin and args.source:
         return git.get_changed_files(args.origin, args.source)
-    elif args.hook_stage == 'commit-msg':
+    elif args.hook_stage in ['prepare-commit-msg', 'commit-msg']:
         return (args.commit_msg_filename,)
     elif args.files:
         return args.files

pre_commit/constants.py

@@ -21,6 +21,6 @@ LOCAL_REPO_VERSION = '1'
 VERSION = importlib_metadata.version('pre_commit')
 
 # `manual` is not invoked by any installed git hook.  See #719
-STAGES = ('commit', 'commit-msg', 'manual', 'push')
+STAGES = ('commit', 'prepare-commit-msg', 'commit-msg', 'manual', 'push')
 
 DEFAULT = 'default'

pre_commit/main.py

@@ -52,7 +52,9 @@ def _add_config_option(parser):
 
 def _add_hook_type_option(parser):
     parser.add_argument(
-        '-t', '--hook-type', choices=('pre-commit', 'pre-push', 'commit-msg'),
+        '-t', '--hook-type', choices=(
+            'pre-commit', 'pre-push', 'prepare-commit-msg', 'commit-msg',
+        ),
         default='pre-commit',
     )
 

pre_commit/resources/hook-tmpl

@@ -161,6 +161,7 @@ def _pre_push(stdin):
 
 def _opts(stdin):
     fns = {
+        'prepare-commit-msg': lambda _: ('--commit-msg-filename', sys.argv[1]),
         'commit-msg': lambda _: ('--commit-msg-filename', sys.argv[1]),
         'pre-commit': lambda _: (),
         'pre-push': _pre_push,

tests/commands/install_uninstall_test.py

@@ -655,7 +655,65 @@ def test_commit_msg_legacy(commit_msg_repo, tempdir_factory, store):
     assert second_line.startswith('Must have "Signed off by:"...')
 
 
-def test_install_disallow_mising_config(tempdir_factory, store):
+def test_prepare_commit_msg_integration_failing(
+        failing_prepare_commit_msg_repo, tempdir_factory, store,
+):
+    install(C.CONFIG_FILE, store, hook_type='prepare-commit-msg')
+    retc, out = _get_commit_output(tempdir_factory)
+    assert retc == 1
+    assert out.startswith('Add "Signed off by:"...')
+    assert out.strip().endswith('...Failed')
+
+
+def test_prepare_commit_msg_integration_passing(
+        prepare_commit_msg_repo, tempdir_factory, store,
+):
+    install(C.CONFIG_FILE, store, hook_type='prepare-commit-msg')
+    msg = 'Hi'
+    retc, out = _get_commit_output(tempdir_factory, msg=msg)
+    assert retc == 0
+    first_line = out.splitlines()[0]
+    assert first_line.startswith('Add "Signed off by:"...')
+    assert first_line.endswith('...Passed')
+    commit_msg_path = os.path.join(
+        prepare_commit_msg_repo, '.git/COMMIT_EDITMSG',
+    )
+    with io.open(commit_msg_path, 'rt') as f:
+        assert 'Signed off by: ' in f.read()
+
+
+def test_prepare_commit_msg_legacy(
+    prepare_commit_msg_repo, tempdir_factory, store,
+):
+    hook_path = os.path.join(
+        prepare_commit_msg_repo, '.git/hooks/prepare-commit-msg',
+    )
+    mkdirp(os.path.dirname(hook_path))
+    with io.open(hook_path, 'w') as hook_file:
+        hook_file.write(
+            '#!/usr/bin/env bash\n'
+            'set -eu\n'
+            'test -e "$1"\n'
+            'echo legacy\n',
+        )
+    make_executable(hook_path)
+
+    install(C.CONFIG_FILE, store, hook_type='prepare-commit-msg')
+
+    msg = 'Hi'
+    retc, out = _get_commit_output(tempdir_factory, msg=msg)
+    assert retc == 0
+    first_line, second_line = out.splitlines()[:2]
+    assert first_line == 'legacy'
+    assert second_line.startswith('Add "Signed off by:"...')
+    commit_msg_path = os.path.join(
+        prepare_commit_msg_repo, '.git/COMMIT_EDITMSG',
+    )
+    with io.open(commit_msg_path, 'rt') as f:
+        assert 'Signed off by: ' in f.read()
+
+
+def test_install_disallow_missing_config(tempdir_factory, store):
     path = make_consuming_repo(tempdir_factory, 'script_hooks_repo')
     with cwd(path):
         remove_config_from_repo(path)
@@ -668,7 +726,7 @@ def test_install_disallow_mising_config(tempdir_factory, store):
         assert ret == 1
 
 
-def test_install_allow_mising_config(tempdir_factory, store):
+def test_install_allow_missing_config(tempdir_factory, store):
     path = make_consuming_repo(tempdir_factory, 'script_hooks_repo')
     with cwd(path):
         remove_config_from_repo(path)

tests/commands/run_test.py

@@ -557,7 +557,12 @@ def test_stages(cap_out, store, repo_with_passing_hook):
                 'language': 'pygrep',
                 'stages': [stage],
             }
-            for i, stage in enumerate(('commit', 'push', 'manual'), 1)
+            for i, stage in enumerate(
+                (
+                    'commit', 'push', 'manual', 'prepare-commit-msg',
+                    'commit-msg',
+                ), 1,
+            )
         ],
     }
     add_config_to_repo(repo_with_passing_hook, config)
@@ -575,6 +580,8 @@ def test_stages(cap_out, store, repo_with_passing_hook):
     assert _run_for_stage('commit').startswith(b'hook 1...')
     assert _run_for_stage('push').startswith(b'hook 2...')
     assert _run_for_stage('manual').startswith(b'hook 3...')
+    assert _run_for_stage('prepare-commit-msg').startswith(b'hook 4...')
+    assert _run_for_stage('commit-msg').startswith(b'hook 5...')
 
 
 def test_commit_msg_hook(cap_out, store, commit_msg_repo):
@@ -593,6 +600,25 @@ def test_commit_msg_hook(cap_out, store, commit_msg_repo):
     )
 
 
+def test_prepare_commit_msg_hook(cap_out, store, prepare_commit_msg_repo):
+    filename = '.git/COMMIT_EDITMSG'
+    with io.open(filename, 'w') as f:
+        f.write('This is the commit message')
+
+    _test_run(
+        cap_out,
+        store,
+        prepare_commit_msg_repo,
+        {'hook_stage': 'prepare-commit-msg', 'commit_msg_filename': filename},
+        expected_outputs=[b'Add "Signed off by:"', b'Passed'],
+        expected_ret=0,
+        stage=False,
+    )
+
+    with io.open(filename, 'rt') as f:
+        assert 'Signed off by: ' in f.read()
+
+
 def test_local_hook_passes(cap_out, store, repo_with_passing_hook):
     config = {
         'repo': 'local',

tests/conftest.py

@@ -14,6 +14,7 @@ from pre_commit import output
 from pre_commit.logging_handler import logging_handler
 from pre_commit.store import Store
 from pre_commit.util import cmd_output
+from pre_commit.util import make_executable
 from testing.fixtures import git_dir
 from testing.fixtures import make_consuming_repo
 from testing.fixtures import write_config
@@ -134,6 +135,54 @@ def commit_msg_repo(tempdir_factory):
         yield path
 
 
+@pytest.fixture
+def prepare_commit_msg_repo(tempdir_factory):
+    path = git_dir(tempdir_factory)
+    script_name = 'add_sign_off.sh'
+    config = {
+        'repo': 'local',
+        'hooks': [{
+            'id': 'add-signoff',
+            'name': 'Add "Signed off by:"',
+            'entry': './{}'.format(script_name),
+            'language': 'script',
+            'stages': ['prepare-commit-msg'],
+        }],
+    }
+    write_config(path, config)
+    with cwd(path):
+        with io.open(script_name, 'w') as script_file:
+            script_file.write(
+                '#!/usr/bin/env bash\n'
+                'set -eu\n'
+                'echo "\nSigned off by: " >> "$1"\n',
+            )
+            make_executable(script_name)
+        cmd_output('git', 'add', '.')
+        git_commit(msg=prepare_commit_msg_repo.__name__)
+        yield path
+
+
+@pytest.fixture
+def failing_prepare_commit_msg_repo(tempdir_factory):
+    path = git_dir(tempdir_factory)
+    config = {
+        'repo': 'local',
+        'hooks': [{
+            'id': 'add-signoff',
+            'name': 'Add "Signed off by:"',
+            'entry': '/usr/bin/env bash -c "exit 1"',
+            'language': 'system',
+            'stages': ['prepare-commit-msg'],
+        }],
+    }
+    write_config(path, config)
+    with cwd(path):
+        cmd_output('git', 'add', '.')
+        git_commit(msg=failing_prepare_commit_msg_repo.__name__)
+        yield path
+
+
 @pytest.fixture(autouse=True, scope='session')
 def dont_write_to_home_directory():
     """pre_commit.store.Store will by default write to the home directory