1 files changed, 72 insertions, 0 deletions
diff --git a/pre_commit_hooks/check_case_conflict.py b/pre_commit_hooks/check_case_conflict.py
new file mode 100644
index 0000000..c3f39db
--- /dev/null
+++ b/pre_commit_hooks/check_case_conflict.py
@@ -0,0 +1,72 @@
+import argparse
+from typing import Iterable
+from typing import Iterator
+from typing import Optional
+from typing import Sequence
+from typing import Set
+
+from pre_commit_hooks.util import added_files
+from pre_commit_hooks.util import cmd_output
+
+
+def lower_set(iterable: Iterable[str]) -> Set[str]:
+    return {x.lower() for x in iterable}
+
+
+def parents(file: str) -> Iterator[str]:
+    path_parts = file.split('/')
+    path_parts.pop()
+    while path_parts:
+        yield '/'.join(path_parts)
+        path_parts.pop()
+
+
+def directories_for(files: Set[str]) -> Set[str]:
+    return {parent for file in files for parent in parents(file)}
+
+
+def find_conflicting_filenames(filenames: Sequence[str]) -> int:
+    repo_files = set(cmd_output('git', 'ls-files').splitlines())
+    repo_files |= directories_for(repo_files)
+    relevant_files = set(filenames) | added_files()
+    relevant_files |= directories_for(relevant_files)
+    repo_files -= relevant_files
+    retv = 0
+
+    # new file conflicts with existing file
+    conflicts = lower_set(repo_files) & lower_set(relevant_files)
+
+    # new file conflicts with other new file
+    lowercase_relevant_files = lower_set(relevant_files)
+    for filename in set(relevant_files):
+        if filename.lower() in lowercase_relevant_files:
+            lowercase_relevant_files.remove(filename.lower())
+        else:
+            conflicts.add(filename.lower())
+
+    if conflicts:
+        conflicting_files = [
+            x for x in repo_files | relevant_files
+            if x.lower() in conflicts
+        ]
+        for filename in sorted(conflicting_files):
+            print(f'Case-insensitivity conflict found: {filename}')
+        retv = 1
+
+    return retv
+
+
+def main(argv: Optional[Sequence[str]] = None) -> int:
+    parser = argparse.ArgumentParser()
+    parser.add_argument(
+        'filenames', nargs='*',
+        help='Filenames pre-commit believes are changed.',
+    )
+
+    args = parser.parse_args(argv)
+
+    return find_conflicting_filenames(args.filenames)
+
+
+if __name__ == '__main__':
+    raise SystemExit(main())