Better impl

packages/executor/src/execution/__tests__/abstract-test.ts

@@ -9,6 +9,7 @@ import {
   GraphQLString,
   GraphQLUnionType,
   parse,
+  versionInfo,
 } from 'graphql';
 import { expectJSON } from '../../__testUtils__/expectJSON.js';
 import { execute, executeSync } from '../execute.js';
@@ -621,5 +622,14 @@ describe('Execute: Handles execution of abstract types', () => {
     expectError({ forTypeName: undefined }).toEqual(
       'Abstract type "Pet" must resolve to an Object type at runtime for field "Query.pet" with value { __typename: undefined }, received "[]".',
     );
+
+    if (versionInfo.major >= 16) {
+      // FIXME: workaround since we can't inject resolveType into SDL
+      // @ts-expect-error
+      assertInterfaceType(schema.getType('Pet')).resolveType = () => schema.getType('Cat');
+      expectError({ forTypeName: undefined }).toEqual(
+        'Support for returning GraphQLObjectType from resolveType was removed in [email protected] please return type name instead.',
+      );
+    }
   });
 });

packages/executor/src/execution/execute.ts

@@ -27,6 +27,7 @@ import {
   SchemaMetaFieldDef,
   TypeMetaFieldDef,
   TypeNameMetaFieldDef,
+  versionInfo,
 } from 'graphql';
 import { ValueOrPromise } from 'value-or-promise';
 import {
@@ -1234,7 +1235,13 @@ function ensureValidRuntimeType(
   }
 
   // releases before 16.0.0 supported returning `GraphQLObjectType` from `resolveType`
+  // TODO: remove in 17.0.0 release
   if (isObjectType(runtimeTypeName)) {
+    if (versionInfo.major >= 16) {
+      throw createGraphQLError(
+        'Support for returning GraphQLObjectType from resolveType was removed in [email protected] please return type name instead.',
+      );
+    }
     runtimeTypeName = runtimeTypeName.name;
   }