Use 'extensions' on GraphQL*Type

Author: IvanGoncharov

src/fake_definition.ts

@@ -267,14 +267,11 @@ export function buildWithFakeDefinitions(
   if (extensionSDL != null) {
     schema = extendSchemaWithAST(schema, parseSDL(extensionSDL));
 
-    // FIXME: put in field extensions
     for (const type of Object.values(schema.getTypeMap())) {
       if (isObjectType(type) || isInterfaceType(type)) {
         for (const field of Object.values(type.getFields())) {
-          const node = field.astNode;
-          if (node && node.loc && node.loc.source === extensionSDL) {
-            (field as any).isExtensionField = true;
-          }
+          const isExtensionField = field.astNode?.loc?.source === extensionSDL;
+          (field.extensions['isExtensionField'] as any) = isExtensionField;
         }
       }
     }

src/proxy.ts

@@ -118,9 +118,10 @@ function stripExtensionFields(schema, operationAST) {
         const fieldDef = typeInfo.getFieldDef();
         if (
           fieldDef.name.startsWith('__') ||
-          (fieldDef as any).isExtensionField
-        )
+          fieldDef.extensions['isExtensionField'] === true
+        ) {
           return null;
+        }
       },
       [Kind.SELECTION_SET]: {
         leave(node) {