Fix skipping fields with union of unsupported type (#722)

Fixes #721

Author: AllanChain

serde/compat.py

@@ -425,7 +425,8 @@ def recursive(cls: TypeLike) -> None:
             stack.append(cls)
             if isinstance(cls, type):
                 for f in dataclass_fields(cls):
-                    recursive(f.type)
+                    if not f.metadata.get("serde_skip"):
+                        recursive(f.type)
             stack.pop()
         elif is_opt(cls):
             args = type_args(cls)

tests/test_basics.py

@@ -867,6 +867,7 @@ def __init__(self, value: int = 42) -> None:
     class Foo:
         name: str
         internal: UnsupportedClass = serde.field(default_factory=UnsupportedClass, skip=True)
+        internal_union: UnsupportedClass | None = serde.field(default=None, skip=True)
 
     # Serialization should work
     f = Foo(name="test")
@@ -876,6 +877,7 @@ class Foo:
     restored = serde.from_dict(Foo, {"name": "test"})
     assert restored.name == "test"
     assert isinstance(restored.internal, UnsupportedClass)
+    assert restored.internal_union is None
 
     # Also test with List of unsupported types
     @serde.serde