Support nested NewType

litestar/_openapi/schema_generation/schema.py

@@ -63,6 +63,7 @@
 from litestar.utils.typing import (
     get_origin_or_inner_type,
     make_non_optional_union,
+    unwrap_new_type,
 )
 
 if TYPE_CHECKING:
@@ -359,7 +360,7 @@ def for_field_definition(self, field_definition: FieldDefinition) -> Schema | Re
     def for_new_type(self, field_definition: FieldDefinition) -> Schema | Reference:
         return self.for_field_definition(
             FieldDefinition.from_kwarg(
-                annotation=field_definition.raw.__supertype__,
+                annotation=unwrap_new_type(field_definition.raw),
                 name=field_definition.name,
                 default=field_definition.default,
             )

litestar/utils/typing.py

@@ -37,7 +37,7 @@
     cast,
 )
 
-from typing_extensions import Annotated, NotRequired, Required, get_args, get_origin, get_type_hints
+from typing_extensions import Annotated, NewType, NotRequired, Required, get_args, get_origin, get_type_hints
 
 from litestar.types.builtin_types import NoneType, UnionTypes
 
@@ -174,6 +174,14 @@ def unwrap_annotation(annotation: Any) -> tuple[Any, tuple[Any, ...], set[Any]]:
     return annotation, tuple(metadata), wrappers
 
 
+def unwrap_new_type(new_type: Any) -> Any:
+    """Unwrap a (nested) ``typing.NewType``"""
+    inner = new_type
+    while isinstance(inner, NewType):
+        inner = inner.__supertype__
+    return inner
+
+
 def get_origin_or_inner_type(annotation: Any) -> Any:
     """Get origin or unwrap it. Returns None for non-generic types.
 

tests/unit/test_openapi/test_parameters.py

@@ -404,3 +404,17 @@ async def handler(
         app.openapi_schema.paths["/{path_param}"].get.responses["200"].content["application/json"].schema.type  # type: ignore[index, union-attr]
         == OpenAPIType.STRING
     )
+
+
+def test_unwrap_nested_new_type() -> None:
+    FancyString = NewType("FancyString", str)
+    FancierString = NewType("FancierString", FancyString)
+
+    @get("/")
+    async def handler(
+        param: FancierString,
+    ) -> None:
+        return None
+
+    app = Litestar([handler])
+    assert app.openapi_schema.paths["/"].get.parameters[0].schema.type == OpenAPIType.STRING  # type: ignore[index, union-attr]