Allow display of custom message when no-commit-to-branch fails

This change should make the failures of no-commit-to-branch easier
for people that might encounter it as maintainers can provide
information about allowed branch names. Current behavior just gives
an opaque error that is not very useful for people that do not have
a lot of knowledge about the project they are contributing to.

README.md

@@ -167,6 +167,7 @@ Protect specific branches from direct checkins.
     branches.
   - `-p` / `--pattern` can be used to protect branches that match a supplied regex
     (e.g. `--pattern, release/.*`). May be specified multiple times.
+  - `-m` / `--message` can be used to customize the error message in case of failure.
 
 Note that `no-commit-to-branch` is configured by default to [`always_run`](https://pre-commit.com/#config-always_run).
 As a result, it will ignore any setting of [`files`](https://pre-commit.com/#config-files),

pre_commit_hooks/no_commit_to_branch.py

@@ -37,11 +37,20 @@ def main(argv: Sequence[str] | None = None) -> int:
             'may be specified multiple times'
         ),
     )
+    parser.add_argument(
+        '-m', '--message', default='',
+        help=(
+            'What message to display if the the check fails'
+        ),
+    )
     args = parser.parse_args(argv)
 
     protected = frozenset(args.branch or ('master', 'main'))
     patterns = frozenset(args.pattern or ())
-    return int(is_on_branch(protected, patterns))
+    result = int(is_on_branch(protected, patterns))
+    if result:
+        print(args.message)
+    return result
 
 
 if __name__ == '__main__':