Serialize unsubstituted type vars as Any

docs/concepts/models.md

@@ -815,7 +815,7 @@ class SerializeAsAnyModel(BaseModel, Generic[BoundT]):
 data_model = DataModel()
 
 print(GenericModel(data=data_model).model_dump())
-#> {'data': {'a': 42}}
+#> {'data': {'a': 42, 'b': 2, 'c': 3}}
 
 
 print(SerializeAsAnyModel(data=data_model).model_dump())

pydantic/_internal/_generate_schema.py

@@ -1450,11 +1450,15 @@ def _unsubstituted_typevar_schema(self, typevar: typing.TypeVar) -> core_schema.
         assert isinstance(typevar, typing.TypeVar)
 
         if typevar.__bound__:
-            return self.generate_schema(typevar.__bound__)
+            schema = self.generate_schema(typevar.__bound__)
         elif typevar.__constraints__:
-            return self._union_schema(typing.Union[typevar.__constraints__])  # type: ignore
+            schema = self._union_schema(typing.Union[typevar.__constraints__])  # type: ignore
         else:
             return core_schema.any_schema()
+        schema['serialization'] = core_schema.wrap_serializer_function_ser_schema(
+            lambda x, h: h(x), schema=core_schema.any_schema()
+        )
+        return schema
 
     def _computed_field_schema(
         self,

pydantic/types.py

@@ -989,6 +989,7 @@ class Foo(BaseModel):
         === ":white_check_mark: Do this"
             ```py
             from decimal import Decimal
+
             from typing_extensions import Annotated
 
             from pydantic import BaseModel, Field
@@ -1080,7 +1081,7 @@ def __hash__(self) -> int:
 ```py
 import uuid
 
-from pydantic import BaseModel, UUID1
+from pydantic import UUID1, BaseModel
 
 class Model(BaseModel):
     uuid1: UUID1
@@ -1094,7 +1095,7 @@ class Model(BaseModel):
 ```py
 import uuid
 
-from pydantic import BaseModel, UUID3
+from pydantic import UUID3, BaseModel
 
 class Model(BaseModel):
     uuid3: UUID3
@@ -1108,7 +1109,7 @@ class Model(BaseModel):
 ```py
 import uuid
 
-from pydantic import BaseModel, UUID4
+from pydantic import UUID4, BaseModel
 
 class Model(BaseModel):
     uuid4: UUID4
@@ -1122,7 +1123,7 @@ class Model(BaseModel):
 ```py
 import uuid
 
-from pydantic import BaseModel, UUID5
+from pydantic import UUID5, BaseModel
 
 class Model(BaseModel):
     uuid5: UUID5

tests/test_generics.py

@@ -2622,3 +2622,26 @@ class Model(Generic[T], BaseModel):
     m1 = Model[int](x=1)
     m2 = Model[int](x=1)
     assert len({m1, m2}) == 1
+
+
+def test_serialize_unsubstituted_typevars_as_any() -> None:
+    ErrorDataT = TypeVar('ErrorDataT', bound=BaseModel)
+
+    class ErrorDetails(BaseModel):
+        foo: str
+
+    class Error(BaseModel, Generic[ErrorDataT]):
+        message: str
+        details: Optional[ErrorDataT]
+
+    sample_error = Error(
+        message='We just had an error',
+        details=ErrorDetails(foo='var'),
+    )
+
+    assert sample_error.model_dump() == {
+        'message': 'We just had an error',
+        'details': {
+            'foo': 'var',
+        },
+    }