Add types to pre-commit

pre_commit/languages/system.py

@@ -1,5 +1,12 @@
+from typing import Sequence
+from typing import Tuple
+from typing import TYPE_CHECKING
+
 from pre_commit.languages import helpers
 
+if TYPE_CHECKING:
+    from pre_commit.repository import Hook
+
 
 ENVIRONMENT_DIR = None
 get_default_version = helpers.basic_get_default_version
@@ -7,5 +14,9 @@ healthy = helpers.basic_healthy
 install_environment = helpers.no_install
 
 
-def run_hook(hook, file_args, color):
+def run_hook(
+        hook: 'Hook',
+        file_args: Sequence[str],
+        color: bool,
+) -> Tuple[int, bytes]:
     return helpers.run_xargs(hook, hook.cmd, file_args, color=color)