1 files changed, 56 insertions, 0 deletions
diff --git a/pre_commit_hooks/check_merge_conflict.py b/pre_commit_hooks/check_merge_conflict.py
new file mode 100644
index 0000000..15ec284
--- /dev/null
+++ b/pre_commit_hooks/check_merge_conflict.py
@@ -0,0 +1,56 @@
+from __future__ import annotations
+
+import argparse
+import os.path
+from typing import Sequence
+
+from pre_commit_hooks.util import cmd_output
+
+
+CONFLICT_PATTERNS = [
+    b'<<<<<<< ',
+    b'======= ',
+    b'=======\r\n',
+    b'=======\n',
+    b'>>>>>>> ',
+]
+
+
+def is_in_merge() -> bool:
+    git_dir = cmd_output('git', 'rev-parse', '--git-dir').rstrip()
+    return (
+        os.path.exists(os.path.join(git_dir, 'MERGE_MSG')) and
+        (
+            os.path.exists(os.path.join(git_dir, 'MERGE_HEAD')) or
+            os.path.exists(os.path.join(git_dir, 'rebase-apply')) or
+            os.path.exists(os.path.join(git_dir, 'rebase-merge'))
+        )
+    )
+
+
+def main(argv: Sequence[str] | None = None) -> int:
+    parser = argparse.ArgumentParser()
+    parser.add_argument('filenames', nargs='*')
+    parser.add_argument('--assume-in-merge', action='store_true')
+    args = parser.parse_args(argv)
+
+    if not is_in_merge() and not args.assume_in_merge:
+        return 0
+
+    retcode = 0
+    for filename in args.filenames:
+        with open(filename, 'rb') as inputfile:
+            for i, line in enumerate(inputfile, start=1):
+                for pattern in CONFLICT_PATTERNS:
+                    if line.startswith(pattern):
+                        print(
+                            f'{filename}:{i}: Merge conflict string '
+                            f'{pattern.strip().decode()!r} found',
+                        )
+                        retcode = 1
+
+    return retcode
+
+
+if __name__ == '__main__':
+    raise SystemExit(main())