Merge pull request #302 from Fatal1ty/fix-union-short-path-for-collections

Don't add short path for collections in Union with no_copy option

Author: Fatal1ty

mashumaro/core/meta/types/pack.py

@@ -329,7 +329,9 @@ def pack_union(
             spec.copy(type=type_arg, expression="value", owner=spec.type)
         )
         if packer not in packers:
-            if packer == "value":
+            if packer == "value" and not issubclass(
+                get_type_origin(type_arg), Collection
+            ):
                 packers.insert(0, packer)
             else:
                 packers.append(packer)
@@ -356,7 +358,9 @@ def pack_union(
                 )
             else:
                 packer_arg_type_check = f"is {packer_arg_type_names[0]}"
-            if packer == "value":
+            if packer == "value" and not issubclass(
+                packer_arg_type, Collection
+            ):
                 with lines.indent(
                     f"if value.__class__ {packer_arg_type_check}:"
                 ):

tests/test_union.py

@@ -5,8 +5,10 @@
 
 import pytest
 
-from mashumaro import DataClassDictMixin
+from mashumaro import DataClassDictMixin, pass_through
 from mashumaro.codecs.basic import encode
+from mashumaro.config import BaseConfig
+from mashumaro.dialect import Dialect
 from tests.utils import same_types
 
 
@@ -139,3 +141,27 @@ def test_union_encoding():
             encoded = encode(value, Union[variants])
             assert value == encoded
             assert same_types(value, encoded)
+
+
+def test_union_no_copy_list_with_dataclass_items_or_passed_through_items():
+    class NoCopyListDialect(Dialect):
+        no_copy_collections = (list,)
+
+    @dataclass
+    class Item(DataClassDictMixin):
+        value: int
+
+    @dataclass
+    class Container(DataClassDictMixin):
+        items: Union[list[Item], list[str]]
+
+        class Config(BaseConfig):
+            dialect = NoCopyListDialect
+            serialization_strategy = {str: {"serialize": lambda x: str(x)}}
+
+    item1 = Item(1)
+    item2 = Item(2)
+    items = [item1, item2]
+    container = Container(items=items)
+    data = container.to_dict()
+    assert data == {"items": [{"value": 1}, {"value": 2}]}