fix(parsing): correctly handle nested discriminated unions

Author: stainless-app[bot]

src/anthropic/_models.py

@@ -5,6 +5,7 @@
 from typing import TYPE_CHECKING, Any, Type, Union, Generic, TypeVar, Callable, Optional, cast
 from datetime import date, datetime
 from typing_extensions import (
+    List,
     Unpack,
     Literal,
     ClassVar,
@@ -382,7 +383,7 @@ def _construct_field(value: object, field: FieldInfo, key: str) -> object:
     if type_ is None:
         raise RuntimeError(f"Unexpected field type is None for {key}")
 
-    return construct_type(value=value, type_=type_)
+    return construct_type(value=value, type_=type_, metadata=getattr(field, "metadata", None))
 
 
 def is_basemodel(type_: type) -> bool:
@@ -436,7 +437,7 @@ def construct_type_unchecked(*, value: object, type_: type[_T]) -> _T:
     return cast(_T, construct_type(value=value, type_=type_))
 
 
-def construct_type(*, value: object, type_: object) -> object:
+def construct_type(*, value: object, type_: object, metadata: Optional[List[Any]] = None) -> object:
     """Loose coercion to the expected type with construction of nested values.
 
     If the given value does not match the expected type then it is returned as-is.
@@ -454,8 +455,10 @@ def construct_type(*, value: object, type_: object) -> object:
         type_ = type_.__value__  # type: ignore[unreachable]
 
     # unwrap `Annotated[T, ...]` -> `T`
-    if is_annotated_type(type_):
-        meta: tuple[Any, ...] = get_args(type_)[1:]
+    if metadata is not None:
+        meta: tuple[Any, ...] = tuple(metadata)
+    elif is_annotated_type(type_):
+        meta = get_args(type_)[1:]
         type_ = extract_type_arg(type_, 0)
     else:
         meta = tuple()

tests/test_models.py

@@ -889,3 +889,48 @@ class ModelB(BaseModel):
     )
 
     assert isinstance(m, ModelB)
+
+
+def test_nested_discriminated_union() -> None:
+    class InnerType1(BaseModel):
+        type: Literal["type_1"]
+
+    class InnerModel(BaseModel):
+        inner_value: str
+
+    class InnerType2(BaseModel):
+        type: Literal["type_2"]
+        some_inner_model: InnerModel
+
+    class Type1(BaseModel):
+        base_type: Literal["base_type_1"]
+        value: Annotated[
+            Union[
+                InnerType1,
+                InnerType2,
+            ],
+            PropertyInfo(discriminator="type"),
+        ]
+
+    class Type2(BaseModel):
+        base_type: Literal["base_type_2"]
+
+    T = Annotated[
+        Union[
+            Type1,
+            Type2,
+        ],
+        PropertyInfo(discriminator="base_type"),
+    ]
+
+    model = construct_type(
+        type_=T,
+        value={
+            "base_type": "base_type_1",
+            "value": {
+                "type": "type_2",
+            },
+        },
+    )
+    assert isinstance(model, Type1)
+    assert isinstance(model.value, InnerType2)