Reject json with duplicate keys? (qmk#18108)

lib/python/qmk/json_schema.py

@@ -10,7 +10,18 @@
 from milc import cli
 
 
-def json_load(json_file):
+def _dict_raise_on_duplicates(ordered_pairs):
+    """Reject duplicate keys."""
+    d = {}
+    for k, v in ordered_pairs:
+        if k in d:
+            raise ValueError("duplicate key: %r" % (k,))
+        else:
+            d[k] = v
+    return d
+
+
+def json_load(json_file, strict=True):
     """Load a json file from disk.
 
     Note: file must be a Path object.
@@ -20,7 +31,7 @@ def json_load(json_file):
         # Not necessary if the data is provided via stdin
         if isinstance(json_file, Path):
             json_file = json_file.open(encoding='utf-8')
-        return hjson.load(json_file)
+        return hjson.load(json_file, object_pairs_hook=_dict_raise_on_duplicates if strict else None)
 
     except (json.decoder.JSONDecodeError, hjson.HjsonDecodeError) as e:
         cli.log.error('Invalid JSON encountered attempting to load {fg_cyan}%s{fg_reset}:\n\t{fg_red}%s', json_file, e)