🔧 Enable checking commit messages from files (#12951)

Adds a new flag --message-file to check-commit

AI-assisted-by: deepseek-flash

scripts/check-commit

@@ -13,6 +13,7 @@ Usage:
   ./scripts/check-commit
   ./scripts/check-commit --commit HEAD~1
   ./scripts/check-commit -c abc1234
+  ./scripts/check-commit --message-file .git/COMMIT_EDITMSG
 """
 
 import argparse
@@ -60,15 +61,23 @@ FORBIDDEN_TRAILER_PATTERN = re.compile(r"^\s*Co-authored-by\s*:", re.IGNORECASE)
 
 URL_PATTERN = re.compile(r"https?://\S+")
 
+# Git appends the staged diff after this marker for `git commit -v` and
+# discards everything after it during cleanup.
+SCISSORS_PATTERN = re.compile(
+    r"^.\s------------------------ >8 ------------------------$",
+    re.MULTILINE,
+)
+
 # ═══════════════════════════════════════════════════════════════════════════════
 # Helpers
 # ═══════════════════════════════════════════════════════════════════════════════
 
-def run_git(args):
+def run_git(args, input_text=None):
     """Run a git command and return (returncode, stdout, stderr)."""
     try:
         result = subprocess.run(
             ["git"] + args,
+            input=input_text,
             capture_output=True,
             text=True,
             check=False,
@@ -91,6 +100,39 @@ def get_commit_message(commit_ref):
     return out.rstrip("\n")
 
 
+def get_message_from_file(path):
+    """Return the commit message stored in *path*.
+
+    The commit-msg hook receives the message before git removes comment
+    lines, so strip them the same way git does before validating.
+    """
+    try:
+        with open(path, encoding="utf-8") as fh:
+            raw = fh.read()
+    except (OSError, UnicodeDecodeError) as exc:
+        print(f"ERROR: could not read message file {path}: {exc}", file=sys.stderr)
+        sys.exit(1)
+
+    scissors = SCISSORS_PATTERN.search(raw)
+    if scissors:
+        raw = raw[:scissors.start()]
+
+    rc, out, err = run_git(["stripspace", "--strip-comments"], input_text=raw)
+    if rc != 0:
+        print(
+            f"ERROR: could not clean message file {path}: {err.strip()}",
+            file=sys.stderr,
+        )
+        sys.exit(1)
+
+    message = out.rstrip("\n")
+    if not message.strip():
+        print(f"ERROR: message file {path} has no commit message", file=sys.stderr)
+        sys.exit(1)
+
+    return message
+
+
 # ═══════════════════════════════════════════════════════════════════════════════
 # Validators
 # ═══════════════════════════════════════════════════════════════════════════════
@@ -243,17 +285,26 @@ def main():
     parser = argparse.ArgumentParser(
         description="Check a commit message against Penpot commit guidelines."
     )
-    parser.add_argument(
+    source = parser.add_mutually_exclusive_group()
+    source.add_argument(
         "-c", "--commit",
-        default="HEAD",
+        metavar="REF",
         help="Commit to check (default: HEAD)",
     )
+    source.add_argument(
+        "-m", "--message-file",
+        metavar="FILE",
+        help="Read the commit message from FILE instead of a commit",
+    )
     args = parser.parse_args()
 
-    commit_ref = args.commit
-    message = get_commit_message(commit_ref)
-
-    print(f"Checking commit {commit_ref} ...\n")
+    if args.message_file is not None:
+        message = get_message_from_file(args.message_file)
+        print(f"Checking commit message in {args.message_file} ...\n")
+    else:
+        commit_ref = args.commit if args.commit is not None else "HEAD"
+        message = get_commit_message(commit_ref)
+        print(f"Checking commit {commit_ref} ...\n")
 
     validators = [
         ("Regex pattern", check_regex),

scripts/test_check_commit.py

@@ -5,15 +5,20 @@ Run with:
 
     python3 scripts/test_check_commit.py
 
-Covers the body line-wrapping validator added to enforce the commit body
-wrap rule documented in .serena/memories/workflow/creating-commits.md.
+Covers the commit message rules enforced by scripts/check-commit and documented
+in .serena/memories/workflow/creating-commits.md.
 """
 
+import contextlib
 import importlib.machinery
 import importlib.util
+import io
+import os
 import pathlib
 import sys
+import tempfile
 import unittest
+import unittest.mock
 
 # Loading scripts/check-commit would otherwise emit scripts/__pycache__/.
 sys.dont_write_bytecode = True
@@ -180,5 +185,71 @@ class SubjectRulesRegressionTests(unittest.TestCase):
         self.assertTrue(ok, error)
 
 
+class MessageFileTests(unittest.TestCase):
+    def setUp(self):
+        self.tmpdir = tempfile.TemporaryDirectory()
+        self.addCleanup(self.tmpdir.cleanup)
+        env = unittest.mock.patch.dict(
+            os.environ,
+            {
+                "GIT_CONFIG_COUNT": "1",
+                "GIT_CONFIG_KEY_0": "core.commentChar",
+                "GIT_CONFIG_VALUE_0": "#",
+            },
+        )
+        env.start()
+        self.addCleanup(env.stop)
+
+    def write_message(self, text):
+        path = pathlib.Path(self.tmpdir.name) / "COMMIT_EDITMSG"
+        path.write_text(text, encoding="utf-8")
+        return str(path)
+
+    def test_reads_message_from_file(self):
+        path = self.write_message(":bug: Fix crash\n\nBody.\n")
+        self.assertEqual(
+            check_commit.get_message_from_file(path),
+            ":bug: Fix crash\n\nBody.",
+        )
+
+    def test_ignores_comment_lines(self):
+        path = self.write_message(
+            ":bug: Fix crash\n\nBody.\n\n"
+            "# Please enter the commit message for your changes.\n"
+            "# " + "long comment " * 20 + "\n"
+        )
+        message = check_commit.get_message_from_file(path)
+        self.assertEqual(message, ":bug: Fix crash\n\nBody.")
+        ok, error = check_commit.check_body_line_length(message)
+        self.assertTrue(ok, error)
+
+    def test_comment_only_file_exits(self):
+        path = self.write_message("# Nothing but a comment\n")
+        with contextlib.redirect_stderr(io.StringIO()):
+            with self.assertRaises(SystemExit):
+                check_commit.get_message_from_file(path)
+
+    def test_ignores_diff_after_scissors_line(self):
+        path = self.write_message(
+            ":bug: Fix crash\n\nBody.\n\n"
+            "# ------------------------ >8 ------------------------\n"
+            "diff --git a/f b/f\n"
+            "+" + "long diff line " * 10 + "\n"
+        )
+        message = check_commit.get_message_from_file(path)
+        self.assertEqual(message, ":bug: Fix crash\n\nBody.")
+
+
+class CommandLineTests(unittest.TestCase):
+    def test_empty_message_file_path_is_rejected(self):
+        argv = ["check-commit", "--message-file", ""]
+        with unittest.mock.patch.object(sys, "argv", argv):
+            with contextlib.redirect_stdout(io.StringIO()):
+                with contextlib.redirect_stderr(io.StringIO()):
+                    with self.assertRaises(SystemExit) as raised:
+                        check_commit.main()
+        self.assertEqual(raised.exception.code, 1)
+
+
 if __name__ == "__main__":
     unittest.main(verbosity=2)