add check-yaml-sorted script and tests

pre_commit_hooks/check_yaml_sorted.py

@@ -0,0 +1,51 @@
+"""Pre-commit hook to check that yaml files are sorted at the top-level.
+
+Does not modify files. Simply parses and compares the stringified values of
+each element of the top-level object.
+
+This allows it to handle all kinds of cases
+- lists of scalars
+- dicts by top-level key
+- lists of dicts by first key name
+- lists of dicts with same keys by first value...
+"""
+from __future__ import annotations
+
+import argparse
+from itertools import tee
+from typing import Any
+from typing import Iterable
+from typing import Sequence
+
+import yaml
+
+
+def is_sorted(iterable: Iterable[Any]) -> bool:
+    a_iter, b_iter = tee(str(e) for e in iterable)
+    next(b_iter, None)
+    for a, b in zip(a_iter, b_iter):
+        if a > b:
+            print(f'Items ({a[:32]}..., {b[:32]}...)')
+            return False
+    return True
+
+
+def main(argv: Sequence[str] | None = None) -> int:
+    parser = argparse.ArgumentParser()
+    parser.add_argument('filenames', nargs='*', help='Filenames to check')
+    args = parser.parse_args(argv)
+
+    retval = 0
+
+    for filename in args.filenames:
+        with open(filename) as fp:
+            data = yaml.safe_load(fp)
+        if not is_sorted(data):
+            print(f'In file {filename}, items are out of order.')
+            retval += 1
+
+    return retval
+
+
+if __name__ == '__main__':
+    raise SystemExit(main())