Add subscribe_field_resolver to execution context

Replicates graphql/graphql-js@6aee19b

Author: Cito

src/graphql/execution/execute.py

@@ -187,6 +187,7 @@ class ExecutionContext:
     variable_values: Dict[str, Any]
     field_resolver: GraphQLFieldResolver
     type_resolver: GraphQLTypeResolver
+    subscribe_field_resolver: GraphQLFieldResolver
     errors: List[GraphQLError]
     middleware_manager: Optional[MiddlewareManager]
 
@@ -202,6 +203,7 @@ def __init__(
         variable_values: Dict[str, Any],
         field_resolver: GraphQLFieldResolver,
         type_resolver: GraphQLTypeResolver,
+        subscribe_field_resolver: GraphQLFieldResolver,
         errors: List[GraphQLError],
         middleware_manager: Optional[MiddlewareManager],
         is_awaitable: Optional[Callable[[Any], bool]],
@@ -214,6 +216,7 @@ def __init__(
         self.variable_values = variable_values
         self.field_resolver = field_resolver  # type: ignore
         self.type_resolver = type_resolver  # type: ignore
+        self.subscribe_field_resolver = subscribe_field_resolver  # type: ignore
         self.errors = errors
         self.middleware_manager = middleware_manager
         if is_awaitable:
@@ -231,6 +234,7 @@ def build(
         operation_name: Optional[str] = None,
         field_resolver: Optional[GraphQLFieldResolver] = None,
         type_resolver: Optional[GraphQLTypeResolver] = None,
+        subscribe_field_resolver: Optional[GraphQLFieldResolver] = None,
         middleware: Optional[Middleware] = None,
         is_awaitable: Optional[Callable[[Any], bool]] = None,
     ) -> Union[List[GraphQLError], "ExecutionContext"]:
@@ -298,6 +302,7 @@ def build(
             coerced_variable_values,  # coerced values
             field_resolver or default_field_resolver,
             type_resolver or default_type_resolver,
+            subscribe_field_resolver or default_field_resolver,
             [],
             middleware_manager,
             is_awaitable,
@@ -978,6 +983,7 @@ def execute(
     operation_name: Optional[str] = None,
     field_resolver: Optional[GraphQLFieldResolver] = None,
     type_resolver: Optional[GraphQLTypeResolver] = None,
+    subscribe_field_resolver: Optional[GraphQLFieldResolver] = None,
     middleware: Optional[Middleware] = None,
     execution_context_class: Optional[Type["ExecutionContext"]] = None,
     is_awaitable: Optional[Callable[[Any], bool]] = None,
@@ -1009,6 +1015,7 @@ def execute(
         operation_name,
         field_resolver,
         type_resolver,
+        subscribe_field_resolver,
         middleware,
         is_awaitable,
     )
@@ -1071,6 +1078,7 @@ def execute_sync(
         operation_name,
         field_resolver,
         type_resolver,
+        None,
         middleware,
         execution_context_class,
         is_awaitable,

src/graphql/execution/subscribe.py

@@ -100,7 +100,7 @@ async def create_source_event_stream(
     context_value: Any = None,
     variable_values: Optional[Dict[str, Any]] = None,
     operation_name: Optional[str] = None,
-    field_resolver: Optional[GraphQLFieldResolver] = None,
+    subscribe_field_resolver: Optional[GraphQLFieldResolver] = None,
 ) -> Union[AsyncIterable[Any], ExecutionResult]:
     """Create source event stream
 
@@ -138,7 +138,7 @@ async def create_source_event_stream(
         context_value,
         variable_values,
         operation_name,
-        field_resolver,
+        subscribe_field_resolver=subscribe_field_resolver,
     )
 
     # Return early errors if execution context failed.
@@ -193,7 +193,7 @@ async def execute_subscription(context: ExecutionContext) -> AsyncIterable[Any]:
 
         # Call the `subscribe()` resolver or the default resolver to produce an
         # AsyncIterable yielding raw payloads.
-        resolve_fn = field_def.subscribe or context.field_resolver
+        resolve_fn = field_def.subscribe or context.subscribe_field_resolver
 
         event_stream = resolve_fn(context.root_value, info, **args)
         if context.is_awaitable(event_stream):

src/graphql/graphql.py

@@ -191,6 +191,7 @@ def graphql_impl(
         operation_name,
         field_resolver,
         type_resolver,
+        None,
         middleware,
         execution_context_class,
         is_awaitable,

tests/execution/test_subscribe.py

@@ -209,6 +209,35 @@ async def foo_generator(_obj, _info):
 
         await subscription.aclose()
 
+    @mark.asyncio
+    async def uses_a_custom_default_subscribe_field_resolver():
+        schema = GraphQLSchema(
+            query=DummyQueryType,
+            subscription=GraphQLObjectType(
+                "Subscription", {"foo": GraphQLField(GraphQLString)}
+            ),
+        )
+
+        class Root:
+            @staticmethod
+            async def custom_foo():
+                yield {"foo": "FooValue"}
+
+        subscription = await subscribe(
+            schema,
+            document=parse("subscription { foo }"),
+            root_value=Root(),
+            subscribe_field_resolver=lambda root, _info: root.custom_foo(),
+        )
+        assert isinstance(subscription, MapAsyncIterator)
+
+        assert await anext(subscription) == (
+            {"foo": "FooValue"},
+            None,
+        )
+
+        await subscription.aclose()
+
     @mark.asyncio
     async def should_only_resolve_the_first_field_of_invalid_multi_field():
         did_resolve = {"foo": False, "bar": False}