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

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',