fix(idempotency): is_missing_idempotency_key iterates dict keys instead of values

aws_lambda_powertools/utilities/idempotency/persistence/base.py

@@ -131,7 +131,13 @@ def _get_hashed_idempotency_key(self, data: dict[str, Any]) -> str | None:
 
     @staticmethod
     def is_missing_idempotency_key(data) -> bool:
-        if isinstance(data, (tuple, list, dict)):
+        if isinstance(data, dict):
+            # Iterating a dict directly walks its keys, not its values, so a dict of
+            # {"user": None, "order": None} (e.g. from a JMESPath multi-select expression
+            # over fields that are all absent from the event) would otherwise be treated
+            # as present just because its keys are non-None strings.
+            return all(x is None for x in data.values())
+        elif isinstance(data, (tuple, list)):
             return all(x is None for x in data)
         elif isinstance(data, (int, float, bool)):
             return False

tests/functional/idempotency/_boto3/test_idempotency.py

@@ -1046,6 +1046,15 @@
     assert BasePersistenceLayer.is_missing_idempotency_key((None, None))
     # GIVEN a dict of Nones THEN is_missing_idempotency_key is True
     assert BasePersistenceLayer.is_missing_idempotency_key({None: None})
+    # GIVEN a dict with non-None keys but all-None values (e.g. from a JMESPath
+    # multi-select expression over event fields that are all absent) THEN
+    # is_missing_idempotency_key is True. Iterating a dict directly walks its keys,
+    # not its values, so this case is not covered by the {None: None} case above,
+    # whose key happens to also be None.
+    assert BasePersistenceLayer.is_missing_idempotency_key({"user": None, "order": None})
+
+    # GIVEN a dict with a real value THEN is_missing_idempotency_key is False
+    assert BasePersistenceLayer.is_missing_idempotency_key({"user": "abc"}) is False
 
     # GIVEN True THEN is_missing_idempotency_key is False
     assert BasePersistenceLayer.is_missing_idempotency_key(True) is False
@@ -1624,7 +1633,7 @@
     def dummy_handler(event, context):
         return {"message": "hi"}
 
     with pytest.warns(PowertoolsUserWarning, match="Disabling idempotency is intended for development environments*"):
         dummy(data=mock_event)
         dummy_handler(mock_event, lambda_context)