Allow to override default type resolver

src/execution/__tests__/executor-test.js

@@ -15,6 +15,7 @@ import { execute } from '../execute';
 import { Kind, parse } from '../../language';
 import {
   GraphQLSchema,
+  GraphQLInterfaceType,
   GraphQLObjectType,
   GraphQLList,
   GraphQLBoolean,
@@ -1029,4 +1030,47 @@ describe('Execute: Handles basic execution tasks', () => {
     const result = execute({ schema, document, fieldResolver });
     expect(result).to.deep.equal({ data: { foo: 'foo' } });
   });
+
+  it('uses a custom type resolver', () => {
+    const document = parse('{ foo { bar } }');
+
+    const fooInterface = new GraphQLInterfaceType({
+      name: 'FooInterface',
+      fields: {
+        bar: { type: GraphQLString },
+      },
+    });
+
+    const fooObject = new GraphQLObjectType({
+      name: 'FooObject',
+      interfaces: [fooInterface],
+      fields: {
+        bar: { type: GraphQLString },
+      },
+    });
+
+    const schema = new GraphQLSchema({
+      query: new GraphQLObjectType({
+        name: 'Query',
+        fields: {
+          foo: { type: fooInterface },
+        },
+      }),
+      types: [fooObject],
+    });
+
+    let possibleTypes;
+    function typeResolver(source, context, info, abstractType) {
+      // Resolver should be able to figure out all possible types on its own
+      possibleTypes = info.schema.getPossibleTypes(abstractType);
+
+      return 'FooObject';
+    }
+
+    const rootValue = { foo: { bar: 'bar' } };
+    const result = execute({ schema, document, rootValue, typeResolver });
+
+    expect(result).to.deep.equal({ data: { foo: { bar: 'bar' } } });
+    expect(possibleTypes).to.deep.equal([fooObject]);
+  });
 });

src/execution/execute.js

@@ -44,6 +44,7 @@ import type {
   GraphQLField,
   GraphQLFieldResolver,
   GraphQLResolveInfo,
+  GraphQLTypeResolver,
   ResponsePath,
   GraphQLList,
 } from '../type/definition';
@@ -102,6 +103,7 @@ export type ExecutionContext = {|
   operation: OperationDefinitionNode,
   variableValues: { [variable: string]: mixed },
   fieldResolver: GraphQLFieldResolver<any, any>,
+  typeResolver: GraphQLTypeResolver<any, any>,
   errors: Array<GraphQLError>,
 |};
 
@@ -124,6 +126,7 @@ export type ExecutionArgs = {|
   variableValues?: ?{ [variable: string]: mixed },
   operationName?: ?string,
   fieldResolver?: ?GraphQLFieldResolver<any, any>,
+  typeResolver?: ?GraphQLTypeResolver<any, any>,
 |};
 
 /**
@@ -151,6 +154,7 @@ declare function execute(
   variableValues?: ?{ [variable: string]: mixed },
   operationName?: ?string,
   fieldResolver?: ?GraphQLFieldResolver<any, any>,
+  typeResolver?: ?GraphQLTypeResolver<any, any>,
 ): MaybePromise<ExecutionResult>;
 export function execute(
   argsOrSchema,
@@ -160,6 +164,7 @@ export function execute(
   variableValues,
   operationName,
   fieldResolver,
+  typeResolver,
 ) {
   /* eslint-enable no-redeclare */
   // Extract arguments from object args if provided.
@@ -172,6 +177,7 @@ export function execute(
         argsOrSchema.variableValues,
         argsOrSchema.operationName,
         argsOrSchema.fieldResolver,
+        argsOrSchema.typeResolver,
       )
     : executeImpl(
         argsOrSchema,
@@ -181,6 +187,7 @@ export function execute(
         variableValues,
         operationName,
         fieldResolver,
+        typeResolver,
       );
 }
 
@@ -192,6 +199,7 @@ function executeImpl(
   variableValues,
   operationName,
   fieldResolver,
+  typeResolver,
 ) {
   // If arguments are missing or incorrect, throw an error.
   assertValidExecutionArguments(schema, document, variableValues);
@@ -206,6 +214,7 @@ function executeImpl(
     variableValues,
     operationName,
     fieldResolver,
+    typeResolver,
   );
 
   // Return early errors if execution context failed.
@@ -301,6 +310,7 @@ export function buildExecutionContext(
   rawVariableValues: ?ObjMap<mixed>,
   operationName: ?string,
   fieldResolver: ?GraphQLFieldResolver<any, any>,
+  typeResolver?: ?GraphQLTypeResolver<any, any>,
 ): $ReadOnlyArray<GraphQLError> | ExecutionContext {
   const errors: Array<GraphQLError> = [];
   let operation: OperationDefinitionNode | void;
@@ -371,6 +381,7 @@ export function buildExecutionContext(
     operation,
     variableValues,
     fieldResolver: fieldResolver || defaultFieldResolver,
+    typeResolver: typeResolver || defaultTypeResolver,
     errors,
   };
 }
@@ -991,9 +1002,9 @@ function completeAbstractValue(
   path: ResponsePath,
   result: mixed,
 ): MaybePromise<ObjMap<mixed>> {
-  const runtimeType = returnType.resolveType
-    ? returnType.resolveType(result, exeContext.contextValue, info)
-    : defaultResolveTypeFn(result, exeContext.contextValue, info, returnType);
+  const resolveTypeFn = returnType.resolveType || exeContext.typeResolver;
+  const contextValue = exeContext.contextValue;
+  const runtimeType = resolveTypeFn(result, contextValue, info, returnType);
 
   if (isPromise(runtimeType)) {
     return runtimeType.then(resolvedRuntimeType =>
@@ -1174,12 +1185,12 @@ function _collectSubfields(
  * Otherwise, test each possible type for the abstract type by calling
  * isTypeOf for the object being coerced, returning the first type that matches.
  */
-function defaultResolveTypeFn(
-  value: mixed,
-  contextValue: mixed,
-  info: GraphQLResolveInfo,
-  abstractType: GraphQLAbstractType,
-): MaybePromise<?GraphQLObjectType | string> {
+export const defaultTypeResolver: GraphQLTypeResolver<any, *> = function(
+  value,
+  contextValue,
+  info,
+  abstractType,
+) {
   // First, look for `__typename`.
   if (
     value !== null &&
@@ -1216,7 +1227,7 @@ function defaultResolveTypeFn(
       }
     });
   }
-}
+};
 
 /**
  * If a resolve function is not given, then a default resolve behavior is used

src/execution/index.js

@@ -7,7 +7,12 @@
  * @flow strict
  */
 
-export { execute, defaultFieldResolver, responsePathAsArray } from './execute';
+export {
+  execute,
+  defaultFieldResolver,
+  defaultTypeResolver,
+  responsePathAsArray,
+} from './execute';
 export { getDirectiveValues } from './values';
 
 export type { ExecutionArgs, ExecutionResult } from './execute';

src/graphql.js

@@ -13,7 +13,10 @@ import { validate } from './validation/validate';
 import { execute } from './execution/execute';
 import type { ObjMap } from './jsutils/ObjMap';
 import type { Source } from './language/source';
-import type { GraphQLFieldResolver } from './type/definition';
+import type {
+  GraphQLFieldResolver,
+  GraphQLTypeResolver,
+} from './type/definition';
 import type { GraphQLSchema } from './type/schema';
 import type { ExecutionResult } from './execution/execute';
 import type { MaybePromise } from './jsutils/MaybePromise';
@@ -61,6 +64,7 @@ export type GraphQLArgs = {|
   variableValues?: ?ObjMap<mixed>,
   operationName?: ?string,
   fieldResolver?: ?GraphQLFieldResolver<any, any>,
+  typeResolver?: ?GraphQLTypeResolver<any, any>,
 |};
 declare function graphql(GraphQLArgs, ..._: []): Promise<ExecutionResult>;
 /* eslint-disable no-redeclare */
@@ -72,6 +76,7 @@ declare function graphql(
   variableValues?: ?ObjMap<mixed>,
   operationName?: ?string,
   fieldResolver?: ?GraphQLFieldResolver<any, any>,
+  typeResolver?: ?GraphQLTypeResolver<any, any>,
 ): Promise<ExecutionResult>;
 export function graphql(
   argsOrSchema,
@@ -81,6 +86,7 @@ export function graphql(
   variableValues,
   operationName,
   fieldResolver,
+  typeResolver,
 ) {
   /* eslint-enable no-redeclare */
   // Always return a Promise for a consistent API.
@@ -96,6 +102,7 @@ export function graphql(
             argsOrSchema.variableValues,
             argsOrSchema.operationName,
             argsOrSchema.fieldResolver,
+            argsOrSchema.typeResolver,
           )
         : graphqlImpl(
             argsOrSchema,
@@ -105,6 +112,7 @@ export function graphql(
             variableValues,
             operationName,
             fieldResolver,
+            typeResolver,
           ),
     ),
   );
@@ -126,6 +134,7 @@ declare function graphqlSync(
   variableValues?: ?ObjMap<mixed>,
   operationName?: ?string,
   fieldResolver?: ?GraphQLFieldResolver<any, any>,
+  typeResolver?: ?GraphQLTypeResolver<any, any>,
 ): ExecutionResult;
 export function graphqlSync(
   argsOrSchema,
@@ -135,6 +144,7 @@ export function graphqlSync(
   variableValues,
   operationName,
   fieldResolver,
+  typeResolver,
 ) {
   /* eslint-enable no-redeclare */
   // Extract arguments from object args if provided.
@@ -148,6 +158,7 @@ export function graphqlSync(
           argsOrSchema.variableValues,
           argsOrSchema.operationName,
           argsOrSchema.fieldResolver,
+          argsOrSchema.typeResolver,
         )
       : graphqlImpl(
           argsOrSchema,
@@ -157,6 +168,7 @@ export function graphqlSync(
           variableValues,
           operationName,
           fieldResolver,
+          typeResolver,
         );
 
   // Assert that the execution was synchronous.
@@ -175,6 +187,7 @@ function graphqlImpl(
   variableValues,
   operationName,
   fieldResolver,
+  typeResolver,
 ): MaybePromise<ExecutionResult> {
   // Validate Schema
   const schemaValidationErrors = validateSchema(schema);
@@ -205,5 +218,6 @@ function graphqlImpl(
     variableValues,
     operationName,
     fieldResolver,
+    typeResolver,
   );
 }

src/index.js

@@ -281,6 +281,7 @@ export type {
 export {
   execute,
   defaultFieldResolver,
+  defaultTypeResolver,
   responsePathAsArray,
   getDirectiveValues,
 } from './execution';

src/type/definition.js

@@ -832,6 +832,7 @@ export type GraphQLTypeResolver<TSource, TContext> = (
   value: TSource,
   context: TContext,
   info: GraphQLResolveInfo,
+  abstractType: GraphQLAbstractType,
 ) => MaybePromise<?GraphQLObjectType | string>;
 
 export type GraphQLIsTypeOfFn<TSource, TContext> = (