Add support for lazy unions

RELEASE.md

@@ -0,0 +1,3 @@
+Release type: patch
+
+Adds support for lazy unions.

strawberry/schema/schema_converter.py

@@ -2,9 +2,11 @@
 
 import dataclasses
 import sys
+import typing
 from functools import partial, reduce
 from typing import (
     TYPE_CHECKING,
+    Annotated,
     Any,
     Callable,
     Generic,
@@ -862,6 +864,10 @@ def from_type(self, type_: Union[StrawberryType, type]) -> GraphQLNullableType:
         if compat.is_graphql_generic(type_):
             raise MissingTypesForGenericError(type_)
 
+        # to handle lazy unions
+        if typing.get_origin(type_) is Annotated and len(typing.get_args(type_)) == 2:
+            type_ = typing.get_args(type_)[1]
+
         if isinstance(type_, EnumDefinition):  # TODO: Replace with StrawberryEnum
             return self.from_enum(type_)
         if compat.is_input_type(type_):  # TODO: Replace with StrawberryInputObject

tests/schema/test_lazy_types/test_lazy_unions.py

@@ -0,0 +1,90 @@
+import textwrap
+from typing import Annotated, Union
+
+import strawberry
+from strawberry.printer import print_schema
+
+
+@strawberry.type
+class TypeA:
+    a: int
+
+
+@strawberry.type
+class TypeB:
+    b: int
+
+
+ABUnion = Annotated[
+    Union[TypeA, TypeB], strawberry.union("ABUnion", types=[TypeA, TypeB])
+]
+
+
+TypeALazy = Annotated[
+    "TypeA", strawberry.lazy("tests.schema.test_lazy_types.test_lazy_unions")
+]
+TypeBLazy = Annotated[
+    "TypeB", strawberry.lazy("tests.schema.test_lazy_types.test_lazy_unions")
+]
+LazyABUnion = Annotated[
+    Union[
+        TypeALazy,
+        TypeBLazy,
+    ],
+    strawberry.union("LazyABUnion", types=[TypeALazy, TypeBLazy]),
+]
+
+
+def test_lazy_union_with_non_lazy_members():
+    @strawberry.type
+    class Query:
+        ab: Annotated[
+            "ABUnion", strawberry.lazy("tests.schema.test_lazy_types.test_lazy_unions")
+        ]
+
+    expected = """
+        union ABUnion = TypeA | TypeB
+
+        type Query {
+          ab: ABUnion!
+        }
+
+        type TypeA {
+          a: Int!
+        }
+
+        type TypeB {
+          b: Int!
+        }
+    """
+
+    schema = strawberry.Schema(query=Query)
+    assert print_schema(schema) == textwrap.dedent(expected).strip()
+
+
+def test_lazy_union_with_lazy_members():
+    @strawberry.type
+    class Query:
+        ab: Annotated[
+            "LazyABUnion",
+            strawberry.lazy("tests.schema.test_lazy_types.test_lazy_unions"),
+        ]
+
+    expected = """
+           union LazyABUnion = TypeA | TypeB
+
+           type Query {
+             ab: LazyABUnion!
+           }
+
+           type TypeA {
+             a: Int!
+           }
+
+           type TypeB {
+             b: Int!
+           }
+       """
+
+    schema = strawberry.Schema(query=Query)
+    assert print_schema(schema) == textwrap.dedent(expected).strip()