Making it possible to invoke pre-commit run --files some.file from a subdirectory of the repository

pre_commit/main.py

@@ -8,6 +8,7 @@ import pkg_resources
 
 from pre_commit import color
 from pre_commit import five
+from pre_commit import git
 from pre_commit.commands.autoupdate import autoupdate
 from pre_commit.commands.clean import clean
 from pre_commit.commands.install_uninstall import install
@@ -110,7 +111,8 @@ def main(argv=None):
         help='Run on all the files in the repo.  Implies --no-stash.',
     )
     run_mutex_group.add_argument(
-        '--files', nargs='*', help='Specific filenames to run hooks on.',
+        '--files', nargs='*', default=[],
+        help='Specific filenames to run hooks on.',
     )
 
     help = subparsers.add_parser(
@@ -122,6 +124,11 @@ def main(argv=None):
     if len(argv) == 0:
         argv = ['run']
     args = parser.parse_args(argv)
+    if args.command == 'run':
+        args.files = [
+            os.path.relpath(os.path.abspath(filename), git.get_root())
+            for filename in args.files
+        ]
 
     if args.command == 'help':
         if args.help_cmd:

pre_commit/runner.py

@@ -24,7 +24,7 @@ class Runner(object):
     def create(cls):
         """Creates a PreCommitRunner by doing the following:
             - Finds the root of the current git repository
-            - chdirs to that directory
+            - chdir to that directory
         """
         root = git.get_root()
         os.chdir(root)

tests/commands/run_test.py

@@ -83,7 +83,8 @@ def _do_run(repo, args, environ={}):
     runner = Runner(repo)
     write_mock = mock.Mock()
     write_fn = functools.partial(sys_stdout_write_wrapper, stream=write_mock)
-    ret = run(runner, args, write=write_fn, environ=environ)
+    with cwd(runner.git_root):  # replicates Runner.create behaviour
+        ret = run(runner, args, write=write_fn, environ=environ)
     printed = get_write_mock_output(write_mock)
     return ret, printed