Support | operator (Union) in PydanticRecursiveRef

pydantic/_internal/_forward_ref.py

@@ -1,6 +1,7 @@
 from __future__ import annotations as _annotations
 
 from dataclasses import dataclass
+from typing import Union
 
 
 @dataclass
@@ -14,3 +15,9 @@ def __call__(self) -> None:
         """Defining __call__ is necessary for the `typing` module to let you use an instance of
         this class as the result of resolving a standard ForwardRef.
         """
+
+    def __or__(self, other):
+        return Union[self, other]  # type: ignore
+
+    def __ror__(self, other):
+        return Union[other, self]  # type: ignore

tests/test_forward_ref.py

@@ -711,6 +711,31 @@ class Foobar(BaseModel):
     assert f.y.model_fields_set == {'x'}
 
 
+@pytest.mark.skipif(sys.version_info < (3, 10), reason='needs 3.10 or newer')
+def test_recursive_models_union(create_module):
+    module = create_module(
+        # language=Python
+        """
+from __future__ import annotations
+
+from pydantic import BaseModel
+from typing import TypeVar, Generic
+
+T = TypeVar("T")
+
+class Foo(BaseModel):
+    bar: Bar[str] | None = None
+    bar2: int | Bar[float]
+
+class Bar(BaseModel, Generic[T]):
+    foo: Foo
+"""
+    )
+    assert module.Foo.model_fields['bar'].annotation == typing.Optional[module.Bar[str]]
+    assert module.Foo.model_fields['bar2'].annotation == typing.Union[int, module.Bar[float]]
+    assert module.Bar.model_fields['foo'].annotation == module.Foo
+
+
 def test_force_rebuild():
     class Foobar(BaseModel):
         b: int