1 files changed, 72 insertions, 0 deletions
diff --git a/pre_commit/meta_hooks/check_useless_excludes.py b/pre_commit/meta_hooks/check_useless_excludes.py
new file mode 100644
index 0000000..30b8d81
--- /dev/null
+++ b/pre_commit/meta_hooks/check_useless_excludes.py
@@ -0,0 +1,72 @@
+import argparse
+import re
+from typing import Optional
+from typing import Sequence
+
+from cfgv import apply_defaults
+
+import pre_commit.constants as C
+from pre_commit import git
+from pre_commit.clientlib import load_config
+from pre_commit.clientlib import MANIFEST_HOOK_DICT
+from pre_commit.commands.run import Classifier
+
+
+def exclude_matches_any(
+        filenames: Sequence[str],
+        include: str,
+        exclude: str,
+) -> bool:
+    if exclude == '^$':
+        return True
+    include_re, exclude_re = re.compile(include), re.compile(exclude)
+    for filename in filenames:
+        if include_re.search(filename) and exclude_re.search(filename):
+            return True
+    return False
+
+
+def check_useless_excludes(config_file: str) -> int:
+    config = load_config(config_file)
+    classifier = Classifier(git.get_all_files())
+    retv = 0
+
+    exclude = config['exclude']
+    if not exclude_matches_any(classifier.filenames, '', exclude):
+        print(
+            f'The global exclude pattern {exclude!r} does not match any files',
+        )
+        retv = 1
+
+    for repo in config['repos']:
+        for hook in repo['hooks']:
+            # Not actually a manifest dict, but this more accurately reflects
+            # the defaults applied during runtime
+            hook = apply_defaults(hook, MANIFEST_HOOK_DICT)
+            names = classifier.filenames
+            types, exclude_types = hook['types'], hook['exclude_types']
+            names = classifier.by_types(names, types, exclude_types)
+            include, exclude = hook['files'], hook['exclude']
+            if not exclude_matches_any(names, include, exclude):
+                print(
+                    f'The exclude pattern {exclude!r} for {hook["id"]} does '
+                    f'not match any files',
+                )
+                retv = 1
+
+    return retv
+
+
+def main(argv: Optional[Sequence[str]] = None) -> int:
+    parser = argparse.ArgumentParser()
+    parser.add_argument('filenames', nargs='*', default=[C.CONFIG_FILE])
+    args = parser.parse_args(argv)
+
+    retv = 0
+    for filename in args.filenames:
+        retv |= check_useless_excludes(filename)
+    return retv
+
+
+if __name__ == '__main__':
+    exit(main())