throw a TypeError when trying to merge a list with a mapping when `me…

…rge_lists=True`

changelog/67092.fixed.md

@@ -0,0 +1 @@
+dictupdate.update: throw a TypeError when trying to merge a list with a mapping when ``merge_lists=True``.

salt/utils/dictupdate.py

@@ -33,6 +33,9 @@ def update(dest, upd, recursive_update=True, merge_lists=False):
     .. versionchanged:: 2016.11.6
         When merging lists, duplicate values are removed. Values already
         present in the ``dest`` list are not added from the ``upd`` list.
+    .. versionchanged:: 3007.2
+        Throw a TypeError when trying to merge a list with a mapping when
+        ``merge_lists=True``.
     """
     if (not isinstance(dest, Mapping)) or (not isinstance(upd, Mapping)):
         raise TypeError("Cannot update using non-dict types in dictupdate.update()")
@@ -56,6 +59,14 @@ def update(dest, upd, recursive_update=True, merge_lists=False):
                     dest[key] = merged
                 else:
                     dest[key] = upd[key]
+            elif (
+                merge_lists
+                and isinstance(dest_subkey, list)
+                and isinstance(val, Mapping)
+            ):
+                raise TypeError(
+                    f"With {merge_lists=} we cannot update list under {key=} with mapping containing keys {val.keys()=} in dictupdate.update()"
+                )
             else:
                 dest[key] = upd[key]
         return dest

tests/unit/utils/test_dictupdate.py

@@ -343,3 +343,15 @@ def test_deep_update_illegal_update(self):
                 dictupdate.update_dict_key_value(
                     {}, "foo", update_with, ordered_dict=True
                 )
+
+    def test_update_with_merge_lists_and_mapping(self):
+        """
+        Test that updating a list with a mapping raises a TypeError
+        when merge_lists=True.
+        """
+        mdict = copy.deepcopy(self.dict1)
+        mdict["A"] = [1, 2]
+        with self.assertRaises(TypeError):
+            dictupdate.update(
+                copy.deepcopy(mdict), {"A": {"key": "value"}}, merge_lists=True
+            )