Fix json_encoders for Enum subclasses (#7029)

pydantic/_internal/_generate_schema.py

@@ -242,7 +242,8 @@ def _add_custom_serialization_from_json_encoders(
         return schema
     # Check the class type and its superclasses for a matching encoder
     # Decimal.__class__.__mro__ (and probably other cases) doesn't include Decimal itself
-    for base in (tp, *tp.__class__.__mro__[:-1]):
+    # if the type is a GenericAlias (e.g. from list[int]) we need to use __class__ instead of .__mro__
+    for base in (tp, *getattr(tp, '__mro__', tp.__class__.__mro__)[:-1]):
         encoder = json_encoders.get(base)
         if encoder is None:
             continue

tests/test_json.py

@@ -7,7 +7,7 @@
 from enum import Enum
 from ipaddress import IPv4Address, IPv4Interface, IPv4Network, IPv6Address, IPv6Interface, IPv6Network
 from pathlib import Path
-from typing import Any, Generator, Optional, Pattern, Union
+from typing import Any, Generator, List, Optional, Pattern, Union
 from uuid import UUID
 
 import pytest
@@ -482,3 +482,21 @@ class Model(BaseModel):
     m = Model(x=1)
     assert m.model_dump() == {'x': 1}
     assert m.model_dump_json() == '{"x":"encoded!"}'
+
+
+def test_json_encoders_types() -> None:
+    class MyEnum(Enum):
+        A = 'a'
+        B = 'b'
+
+    class A(BaseModel):
+        a: MyEnum
+        b: List[int]
+        c: Decimal
+        model_config = ConfigDict(
+            json_encoders={Enum: lambda val: val.name, List[int]: lambda val: 'list!', Decimal: lambda val: 'decimal!'}
+        )
+
+    m = A(a=MyEnum.A, b=[1, 2, 3], c=Decimal('0'))
+    assert m.model_dump_json() == '{"a":"A","b":"list!","c":"decimal!"}'
+    assert m.model_dump() == {'a': MyEnum.A, 'b': [1, 2, 3], 'c': Decimal('0')}