Fix fragment filtering edge case when a type implements multiple interfaces

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ### vNEXT
 
+* Fix a bug where inline fragments got filtered in merged schemas when a type implemented multiple interfaces [PR #546](https://github.com/apollographql/graphql-tools/pull/546)
 * IEnumResolver value can be a `number` type
 
 ### v2.17.0

src/stitching/delegateToSchema.ts

@@ -510,6 +510,11 @@ function implementsAbstractType(
     child instanceof GraphQLObjectType
   ) {
     return child.getInterfaces().indexOf(parent) !== -1;
+  } else if (
+    parent instanceof GraphQLInterfaceType &&
+    child instanceof GraphQLInterfaceType
+  ) {
+    return true;
   } else if (
     parent instanceof GraphQLUnionType &&
     child instanceof GraphQLObjectType

src/test/testMergeSchemas.ts

@@ -13,27 +13,36 @@ import {
 import mergeSchemas from '../stitching/mergeSchemas';
 import {
   propertySchema as localPropertySchema,
+  productSchema as localProductSchema,
   bookingSchema as localBookingSchema,
   subscriptionSchema as localSubscriptionSchema,
   remoteBookingSchema,
   remotePropertySchema,
+  remoteProductSchema,
   subscriptionPubSub,
   subscriptionPubSubTrigger,
 } from './testingSchemas';
 import { forAwaitEach } from 'iterall';
 import { makeExecutableSchema } from '../schemaGenerator';
 
 const testCombinations = [
-  { name: 'local', booking: localBookingSchema, property: localPropertySchema },
+  {
+    name: 'local',
+    booking: localBookingSchema,
+    property: localPropertySchema,
+    product: localProductSchema,
+  },
   {
     name: 'remote',
     booking: remoteBookingSchema,
     property: remotePropertySchema,
+    product: remoteProductSchema,
   },
   {
     name: 'hybrid',
     booking: localBookingSchema,
     property: remotePropertySchema,
+    product: localProductSchema,
   },
 ];
 
@@ -101,7 +110,6 @@ let linkSchema = `
     id: ID!
   }
 
-
   extend type Booking implements Node {
     """
     The property of the booking.
@@ -222,16 +230,19 @@ testCombinations.forEach(async combination => {
   describe('merging ' + combination.name, () => {
     let mergedSchema: GraphQLSchema,
       propertySchema: GraphQLSchema,
+      productSchema: GraphQLSchema,
       bookingSchema: GraphQLSchema;
 
     before(async () => {
       propertySchema = await combination.property;
       bookingSchema = await combination.booking;
+      productSchema = await combination.product;
 
       mergedSchema = mergeSchemas({
         schemas: [
           propertySchema,
           bookingSchema,
+          productSchema,
           scalarTest,
           enumTest,
           linkSchema,
@@ -1820,6 +1831,39 @@ bookingById(id: $b1) {
       //   });
       // });
 
+      it('multi-interface filter', async () => {
+        const result = await graphql(
+          mergedSchema,
+          `
+            query {
+              products {
+                id
+                __typename
+                ... on Sellable {
+                  price
+                }
+              }
+            }
+          `,
+        );
+
+        expect(result).to.deep.equal({
+          data: {
+            products: [
+              {
+                id: 'pd1',
+                __typename: 'SimpleProduct',
+                price: 100,
+              },
+              {
+                id: 'pd2',
+                __typename: 'DownloadableProduct',
+              },
+            ],
+          },
+        });
+      });
+
       it('arbitrary transforms that return interfaces', async () => {
         const result = await graphql(
           mergedSchema,

src/test/testingSchemas.ts

@@ -25,6 +25,13 @@ export type Property = {
   };
 };
 
+export type Product = {
+  id: string;
+  price?: number;
+  url?: string,
+  type: string,
+};
+
 export type Booking = {
   id: string;
   propertyId: string;
@@ -49,10 +56,23 @@ export type Vehicle = {
 
 export const sampleData: {
   Property: { [key: string]: Property };
+  Product: { [key: string]: Product };
   Booking: { [key: string]: Booking };
   Customer: { [key: string]: Customer };
   Vehicle: { [key: string]: Vehicle };
 } = {
+  Product: {
+    pd1: {
+      id: 'pd1',
+      type: 'simple',
+      price: 100,
+    },
+    pd2: {
+      id: 'pd2',
+      type: 'download',
+      url: 'https://graphql.org',
+    },
+  },
   Property: {
     p1: {
       id: 'p1',
@@ -349,6 +369,53 @@ const propertyResolvers: IResolvers = {
   },
 };
 
+const productTypeDefs = `
+  interface Product {
+    id: ID!
+  }
+
+  interface Sellable {
+    price: Int!
+  }
+
+  interface Downloadable {
+    url: String!
+  }
+
+  type SimpleProduct implements Product, Sellable {
+    id: ID!
+    price: Int!
+  }
+
+  type DownloadableProduct implements Product, Downloadable {
+    id: ID!
+    url: String!
+  }
+
+  type Query {
+    products: [Product]
+  }
+`;
+
+const productResolvers: IResolvers = {
+  Query: {
+    products(root) {
+      const list = values(sampleData.Product);
+      return list;
+    },
+  },
+
+  Product: {
+    __resolveType(obj) {
+      if (obj.type === 'simple') {
+        return 'SimpleProduct';
+      } else {
+        return 'DownloadableProduct';
+      }
+    },
+  },
+};
+
 const customerAddressTypeDef = `
   type Customer implements Person {
     id: ID!
@@ -551,6 +618,11 @@ export const propertySchema: GraphQLSchema = makeExecutableSchema({
   resolvers: propertyResolvers,
 });
 
+export const productSchema: GraphQLSchema = makeExecutableSchema({
+  typeDefs: productTypeDefs,
+  resolvers: productResolvers,
+});
+
 export const bookingSchema: GraphQLSchema = makeExecutableSchema({
   typeDefs: bookingAddressTypeDefs,
   resolvers: bookingResolvers,
@@ -648,6 +720,7 @@ async function makeExecutableSchemaFromFetcher(schema: GraphQLSchema) {
 }
 
 export const remotePropertySchema = makeSchemaRemoteFromLink(propertySchema);
+export const remoteProductSchema = makeSchemaRemoteFromLink(productSchema);
 export const remoteBookingSchema = makeExecutableSchemaFromFetcher(
   bookingSchema,
 );