fix: add default encoders for Enums and EnumMeta (#3193)

* fix: add default encoders for Enums

* chore: revert linting change

litestar/serialization/msgspec_hooks.py

@@ -3,6 +3,7 @@
 from collections import deque
 from datetime import date, datetime, time
 from decimal import Decimal
+from enum import Enum, EnumMeta
 from functools import partial
 from ipaddress import (
     IPv4Address,
@@ -52,6 +53,8 @@
     deque: list,
     Decimal: lambda val: int(val) if val.as_tuple().exponent >= 0 else float(val),
     Pattern: lambda val: val.pattern,
+    Enum: lambda val: val.value if val else None,
+    EnumMeta: lambda val: None,
     # support subclasses of stdlib types, If no previous type matched, these will be
     # the last type in the mro, so we use this to (attempt to) convert a subclass into
     # its base class. # see https://github.com/jcrist/msgspec/issues/248

tests/unit/test_response/test_base_response.py

@@ -1,3 +1,4 @@
+from enum import Enum
 from pathlib import PurePosixPath
 from typing import Any, Optional
 
@@ -187,6 +188,15 @@ def test_get_serializer() -> None:
     class Foo:
         pass
 
+    class Color(Enum):
+        RED = 1
+
+    class Size(str, Enum):
+        SMALL = "small"
+
+    class AltSize(Enum):
+        OTHER = "another"
+
     foo_encoder = {Foo: lambda f: "it's a foo"}
     path_encoder = {PurePosixPath: lambda p: "it's a path"}
 
@@ -202,6 +212,9 @@ class FooResponse(Response):
     assert (
         get_serializer(FooResponse(None, type_encoders={Foo: lambda f: "foo"}).response_type_encoders)(Foo()) == "foo"
     )
+    assert get_serializer()(Color.RED) == Color.RED.value
+    assert get_serializer()(Size(Size.SMALL)) == "Size.SMALL"
+    assert get_serializer()(AltSize) is None
 
 
 def test_head_response_doesnt_support_content() -> None: