fix(smithy-aws-core): omit Result wrapper for empty awsQuery output

packages/smithy-aws-core/.changes/next-release/smithy-aws-core-bugfix-05435b3fb9a54b86b4ebb4d61b0d13ae.json

@@ -0,0 +1,4 @@
+{
+  "type": "bugfix",
+  "description": "Fixed awsQuery response deserialization for operations with no output members."
+}

packages/smithy-aws-core/src/smithy_aws_core/aio/protocols.py

@@ -364,10 +364,14 @@ def _action_name(
     def _response_wrapper_elements(
         self,
         operation: APIOperation[SerializeableShape, DeserializeableShape],
-    ) -> tuple[str, str]:
+    ) -> tuple[str, ...]:
+        name = operation.schema.id.name
+        # Operations with no output members will omit the <OpResult> element.
+        if not operation.output_schema.members:
+            return (f"{name}Response",)
         return (
-            f"{operation.schema.id.name}Response",
-            f"{operation.schema.id.name}Result",
+            f"{name}Response",
+            f"{name}Result",
         )
 
     def _error_wrapper_elements(self) -> tuple[str, ...]:

packages/smithy-aws-core/tests/unit/aio/test_protocols.py

@@ -131,6 +131,9 @@ def test_aws_json_document_discriminator(
     ],
     members={"message": {"target": STRING}},
 )
+_EMPTY_OUTPUT_SCHEMA = Schema.collection(
+    id=ShapeID("com.test#EmptyOutput"),
+)
 
 
 @dataclass
@@ -160,6 +163,16 @@ def _consumer(schema: Schema, de: ShapeDeserializer) -> None:
         return cls(**kwargs)
 
 
+class _EmptyOutput:
+    @classmethod
+    def deserialize(cls, deserializer: ShapeDeserializer) -> "_EmptyOutput":
+        def _consumer(schema: Schema, de: ShapeDeserializer) -> None:
+            pass
+
+        deserializer.read_struct(_EMPTY_OUTPUT_SCHEMA, consumer=_consumer)
+        return cls()
+
+
 def _operation_schema(name: str) -> Schema:
     return Schema(
         id=ShapeID(f"com.test#{name}"),
@@ -171,10 +184,14 @@ def _mock_operation(
     schema: Schema,
     *,
     error_schemas: list[Schema] | None = None,
+    output: Any = None,
+    output_schema: Schema | None = None,
 ) -> APIOperation[Any, Any]:
     operation = Mock(spec=APIOperation)
     operation.schema = schema
     operation.error_schemas = error_schemas or []
+    operation.output = output
+    operation.output_schema = output_schema
     return cast("APIOperation[Any, Any]", operation)
 
 
@@ -272,3 +289,28 @@ async def test_aws_query_returns_generic_error_for_unknown_code() -> None:
         "Unknown error for operation com.test#FailingOperation"
         " - status: 500, code: UnknownThing"
     )
+
+
+async def test_aws_query_deserializes_empty_output_without_result_wrapper() -> None:
+    protocol = AwsQueryClientProtocol(_SERVICE_SCHEMA, "2020-01-08")
+    result = await protocol.deserialize_response(
+        operation=_mock_operation(
+            _operation_schema("EmptyOperation"),
+            output=_EmptyOutput,
+            output_schema=_EMPTY_OUTPUT_SCHEMA,
+        ),
+        request=cast(HTTPRequest, Mock()),
+        response=HTTPResponse(
+            status=200,
+            fields=tuples_to_fields([]),
+            body=(
+                b"<EmptyOperationResponse>"
+                b"<ResponseMetadata><RequestId>abc-123</RequestId></ResponseMetadata>"
+                b"</EmptyOperationResponse>"
+            ),
+        ),
+        error_registry=TypeRegistry({}),
+        context=TypedProperties(),
+    )
+
+    assert isinstance(result, _EmptyOutput)