Check that labels are synced when dumping variants.json

Signed-off-by: Michał Górny <mgorny@quansight.com>

Author: mgorny

variantlib/variants_json.py

@@ -90,6 +90,8 @@ def providers_dict(self) -> dict[str, dict[str, str | list[str] | bool]]:
     def to_str(self) -> str:
         """Serialize variants.json as a JSON string"""
 
+        assert all(label == vdesc.label for label, vdesc in self.variants.items())
+
         data: dict[str, Any] = {
             VARIANTS_JSON_SCHEMA_KEY: VARIANTS_JSON_SCHEMA_URL,
             VARIANT_INFO_DEFAULT_PRIO_KEY: dict(self._priorities_to_json()),