refactor: add execution mode/serially argument to execute_root_selection_set

The analog of executeRootSelectionSet() is Executor.execute_operation(),
which kept its name, so the argument was added there.

Replicates graphql/graphql-js@cf0de41

Author: Cito

src/graphql/execution/execute.py

@@ -441,6 +441,7 @@ def build_per_event_executor(self, payload: Any) -> Executor:
 
     def execute_operation(
         self,
+        serially: bool | None = None,
     ) -> AwaitableOrValue[ExecutionResult | ExperimentalIncrementalExecutionResults]:
         """Execute an operation.
 
@@ -500,7 +501,13 @@ def execute_operation(
                 )
                 if new_defer_usages
                 else self.execute_root_grouped_field_set(
-                    operation_type, root_type, root_value, grouped_field_set, None
+                    root_type,
+                    root_value,
+                    grouped_field_set,
+                    operation_type == OperationType.MUTATION
+                    if serially is None
+                    else serially,
+                    None,
                 )
             )
 
@@ -579,18 +586,14 @@ def execute_execution_plan(
 
     def execute_root_grouped_field_set(
         self,
-        operation: OperationType,
         root_type: GraphQLObjectType,
         root_value: Any,
         grouped_field_set: GroupedFieldSet,
+        serially: bool,
         defer_map: RefMap[DeferUsage, DeferredFragmentRecord] | None,
     ) -> AwaitableOrValue[GraphQLWrappedResult[dict[str, Any]]]:
         """Execute the root grouped field set."""
-        return (
-            self.execute_fields_serially
-            if operation == OperationType.MUTATION
-            else self.execute_fields
-        )(
+        return (self.execute_fields_serially if serially else self.execute_fields)(
             root_type,
             root_value,
             None,
@@ -3028,7 +3031,7 @@ def execute_subscription_event(
     The passed executor should be a per-event executor as created by
     :meth:`Executor.build_per_event_executor`.
     """
-    return execute_root_selection_set(executor)
+    return cast("AwaitableOrValue[ExecutionResult]", executor.execute_operation(False))
 
 
 def create_source_event_stream(

tests/execution/test_executor.py

@@ -7,7 +7,12 @@
 import pytest
 
 from graphql.error import GraphQLError
-from graphql.execution import Executor, execute, execute_sync
+from graphql.execution import (
+    Executor,
+    execute,
+    execute_root_selection_set,
+    execute_sync,
+)
 from graphql.execution.collect_fields import FieldDetails
 from graphql.execution.get_variable_signature import GraphQLVariableSignature
 from graphql.execution.values import VariableValues, VariableValueSource
@@ -55,6 +60,19 @@ def accepts_positional_arguments():
 
         assert result == ({"a": "rootValue"}, None)
 
+    def executes_the_root_selection_set_of_a_built_executor():
+        schema = GraphQLSchema(
+            GraphQLObjectType(
+                "Type",
+                {"a": GraphQLField(GraphQLString, resolve=lambda obj, *_args: obj)},
+            )
+        )
+
+        executor = Executor.build(schema, parse("{ a }"), "rootValue")
+        assert isinstance(executor, Executor)
+
+        assert execute_root_selection_set(executor) == ({"a": "rootValue"}, None)
+
     async def executes_arbitrary_code():
         class Data:
             def a(self, _info):