Restrict Thunks to support only ObjMap and Array (#2952)

Author: IvanGoncharov

integrationTests/ts/index.ts

@@ -31,7 +31,7 @@ declare module 'graphql' {
 
 const queryType: GraphQLObjectType = new GraphQLObjectType({
   name: 'Query',
-  fields: {
+  fields: () => ({
     sayHi: {
       type: GraphQLString,
       args: {
@@ -47,7 +47,7 @@ const queryType: GraphQLObjectType = new GraphQLObjectType({
         someFieldExtension: example,
       },
     },
-  },
+  }),
   extensions: {
     someObjectExtension: example,
   },

src/type/definition.d.ts

@@ -263,7 +263,9 @@ export function getNamedType(type: GraphQLType): GraphQLNamedType;
  * Used while defining GraphQL types to allow for circular references in
  * otherwise immutable type definitions.
  */
-export type Thunk<T> = (() => T) | T;
+export type Thunk<T extends { [key: string]: any } | Array<any>> =
+  | (() => T)
+  | T;
 
 /**
  * Custom extensions

src/type/definition.js

@@ -511,10 +511,9 @@ export function getNamedType(type) {
  * Used while defining GraphQL types to allow for circular references in
  * otherwise immutable type definitions.
  */
-export type Thunk<+T> = (() => T) | T;
+export type Thunk<+T: ObjMap<any> | Array<any>> = (() => T) | T;
 
-function resolveThunk<+T>(thunk: Thunk<T>): T {
-  // $FlowFixMe[incompatible-use]
+function resolveThunk<+T: ObjMap<any> | Array<any>>(thunk: Thunk<T>): T {
   return typeof thunk === 'function' ? thunk() : thunk;
 }