build_schema: allow to reference introspection types

Replicates graphql/graphql-js@1597f5d

Author: Cito

src/graphql/validation/rules/known_type_names.py

@@ -9,7 +9,7 @@
     NamedTypeNode,
     TypeDefinitionNode,
 )
-from ...type import specified_scalar_types
+from ...type import introspection_types, specified_scalar_types
 from ...pyutils import did_you_mean, suggestion_list
 from . import ASTValidationRule, ValidationContext, SDLValidationContext
 
@@ -55,12 +55,12 @@ def enter_named_type(
             except IndexError:
                 definition_node = parent
             is_sdl = is_sdl_node(definition_node)
-            if is_sdl and type_name in specified_scalar_types:
+            if is_sdl and type_name in standard_type_names:
                 return
 
             suggested_types = suggestion_list(
                 type_name,
-                list(specified_scalar_types) + self.type_names
+                list(standard_type_names) + self.type_names
                 if is_sdl
                 else self.type_names,
             )
@@ -72,6 +72,9 @@ def enter_named_type(
             )
 
 
+standard_type_names = set(specified_scalar_types).union(introspection_types)
+
+
 def is_sdl_node(value: Union[Node, Collection[Node], None]) -> bool:
     return (
         value is not None

tests/utilities/test_build_ast_schema.py

@@ -28,6 +28,7 @@
     assert_object_type,
     assert_scalar_type,
     assert_union_type,
+    introspection_types,
     validate_schema,
 )
 from graphql.utilities import build_ast_schema, build_schema, print_schema, print_type
@@ -1208,6 +1209,35 @@ def can_build_invalid_schema():
         errors = validate_schema(schema)
         assert errors
 
+    def do_not_override_standard_types():
+        # Note: not sure it's desired behaviour to just silently ignore override
+        # attempts so just documenting it here.
+
+        schema = build_schema(
+            """
+            scalar ID
+
+            scalar __Schema
+            """
+        )
+
+        assert schema.get_type("ID") is GraphQLID
+        assert schema.get_type("__Schema") is introspection_types["__Schema"]
+
+    def allows_to_reference_introspection_types():
+        schema = build_schema(
+            """
+            type Query {
+              introspectionField: __EnumValue
+            }
+            """
+        )
+
+        query_type = assert_object_type(schema.get_type("Query"))
+        __EnumValue = introspection_types["__EnumValue"]
+        assert query_type.fields["introspectionField"].type is __EnumValue
+        assert schema.get_type("__EnumValue") is introspection_types["__EnumValue"]
+
     def rejects_invalid_sdl():
         sdl = """
             type Query {