Support docker hooks with args

pre_commit/languages/docker.py

@@ -81,14 +81,17 @@ def run_hook(repo_cmd_runner, hook, file_args):
     # Rebuild the docker image in case it has gone missing, as many people do
     # automated cleanup of docker images.
     build_docker_image(repo_cmd_runner, pull=False)
+
+    entry_parts = hook['entry'].split(' ')
+    entry_executable, entry_args = entry_parts[0], entry_parts[1:]
+
     cmd = (
         'docker', 'run',
         '--rm',
-        '-u', '{}:{}'.format(os.getuid(), os.getgid()),
         '-v', '{}:/src:rw'.format(os.getcwd()),
         '--workdir', '/src',
-        '--entrypoint', hook['entry'],
+        '--entrypoint', entry_executable,
         docker_tag(repo_cmd_runner)
     )
 
-    return xargs(cmd + tuple(hook['args']), file_args)
+    return xargs(cmd + tuple(entry_args) + tuple(hook['args']), file_args)

testing/resources/docker_hooks_repo/hooks.yaml

@@ -4,6 +4,12 @@
     language: docker
     files: \.txt$
 
+-   id: docker-hook-arg
+    name: Docker test hook
+    entry: echo -n
+    language: docker
+    files: \.txt$
+
 -   id: docker-hook-failing
     name: Docker test hook with nonzero exit code
     entry: bork

tests/repository_test.py

@@ -141,6 +141,17 @@ def test_run_a_docker_hook(tempdir_factory, store):
     )
 
 
+@skipif_slowtests_false
+@skipif_cant_run_docker
+@pytest.mark.integration
+def test_run_a_docker_hook_with_entry_args(tempdir_factory, store):
+    _test_hook_repo(
+        tempdir_factory, store, 'docker_hooks_repo',
+        'docker-hook-arg',
+        ['Hello World from docker'], b'Hello World from docker',
+    )
+
+
 @skipif_slowtests_false
 @skipif_cant_run_docker
 @pytest.mark.integration