Add support for commit-msg git hook

pre_commit/commands/install_uninstall.py

@@ -56,16 +56,21 @@ def install(
 
     with io.open(hook_path, 'w') as pre_commit_file_obj:
         if hook_type == 'pre-push':
-            with io.open(resource_filename('pre-push-tmpl')) as fp:
-                pre_push_contents = fp.read()
+            with io.open(resource_filename('pre-push-tmpl')) as f:
+                hook_specific_contents = f.read()
+        elif hook_type == 'commit-msg':
+            with io.open(resource_filename('commit-msg-tmpl')) as f:
+                hook_specific_contents = f.read()
+        elif hook_type == 'pre-commit':
+            hook_specific_contents = ''
         else:
-            pre_push_contents = ''
+            raise AssertionError('Unknown hook type: {}'.format(hook_type))
 
         skip_on_missing_conf = 'true' if skip_on_missing_conf else 'false'
         contents = io.open(resource_filename('hook-tmpl')).read().format(
             sys_executable=sys.executable,
             hook_type=hook_type,
-            pre_push=pre_push_contents,
+            hook_specific=hook_specific_contents,
             skip_on_missing_conf=skip_on_missing_conf,
         )
         pre_commit_file_obj.write(contents)

pre_commit/commands/run.py

@@ -58,6 +58,9 @@ def get_filenames(args, include_expr, exclude_expr):
         getter = git.get_files_matching(
             lambda: get_changed_files(args.origin, args.source),
         )
+    elif args.hook_stage == 'commit-msg':
+        def getter(*_):
+            return (args.commit_msg_filename,)
     elif args.files:
         getter = git.get_files_matching(lambda: args.files)
     elif args.all_files:

pre_commit/main.py

@@ -76,7 +76,7 @@ def main(argv=None):
         ),
     )
     install_parser.add_argument(
-        '-t', '--hook-type', choices=('pre-commit', 'pre-push'),
+        '-t', '--hook-type', choices=('pre-commit', 'pre-push', 'commit-msg'),
         default='pre-commit',
     )
     install_parser.add_argument(
@@ -149,6 +149,10 @@ def main(argv=None):
         '--source', '-s',
         help="The remote branch's commit_id when using `git push`.",
     )
+    run_parser.add_argument(
+        '--commit-msg-filename',
+        help='Filename to check when running during `commit-msg`',
+    )
     run_parser.add_argument(
         '--allow-unstaged-config', default=False, action='store_true',
         help=(
@@ -157,7 +161,8 @@ def main(argv=None):
         ),
     )
     run_parser.add_argument(
-        '--hook-stage', choices=('commit', 'push'), default='commit',
+        '--hook-stage', choices=('commit', 'push', 'commit-msg'),
+        default='commit',
         help='The stage during which the hook is fired e.g. commit or push.',
     )
     run_parser.add_argument(

pre_commit/resources/commit-msg-tmpl

@@ -0,0 +1 @@
+args="run --hook-stage=commit-msg --commit-msg-filename=$1"

pre_commit/resources/hook-tmpl

@@ -52,7 +52,7 @@ if [ ! -f $CONF_FILE  ]; then
 	fi
 fi
 
-{pre_push}
+{hook_specific}
 
 # Run pre-commit
 if ((WHICH_RETV == 0)); then