fix(federation): Aggregate interfaces for types and interfaces

packages/apollo-federation/CHANGELOG.md

@@ -6,6 +6,7 @@
 
 - __FIX__: CSDL complex `@key`s shouldn't result in an unparseable document [PR #4490](https://github.com/apollographql/apollo-server/pull/4490)
 - __FIX__: Value type validations - restrict unions, scalars, enums [PR #4496](https://github.com/apollographql/apollo-server/pull/4496)
+- __FIX__: Composition - aggregate interfaces for types and interfaces in composed schema [PR #4497](https://github.com/apollographql/apollo-server/pull/4497)
 
 ## v0.19.1
 

packages/apollo-federation/src/composition/__tests__/composeAndValidate.test.ts

@@ -5,6 +5,7 @@ import {
   DocumentNode,
   GraphQLScalarType,
   specifiedDirectives,
+  printSchema,
 } from 'graphql';
 import {
   astSerializer,
@@ -555,6 +556,83 @@ describe('composition of value types', () => {
       `);
     });
   });
+
+  it('composed type implements ALL interfaces that value types implement', () => {
+    const serviceA = {
+      typeDefs: gql`
+        interface Node {
+          id: ID!
+        }
+
+        interface Named {
+          name: String
+        }
+
+        type Product implements Named & Node {
+          id: ID!
+          name: String
+        }
+
+        type Query {
+          node(id: ID!): Node
+        }
+      `,
+      name: 'serviceA',
+    };
+
+    const serviceB = {
+      typeDefs: gql`
+        interface Node {
+          id: ID!
+        }
+
+        type Product implements Node {
+          id: ID!
+          name: String
+        }
+      `,
+      name: 'serviceB',
+    };
+
+    const serviceC = {
+      typeDefs: gql`
+        interface Named {
+          name: String
+        }
+
+        type Product implements Named {
+          id: ID!
+          name: String
+        }
+      `,
+      name: 'serviceC',
+    };
+
+    const serviceD = {
+      typeDefs: gql`
+        type Product {
+          id: ID!
+          name: String
+        }
+      `,
+      name: 'serviceD',
+    };
+
+    const { schema, errors, composedSdl } = composeAndValidate([
+      serviceA,
+      serviceB,
+      serviceC,
+      serviceD,
+    ]);
+
+    expect(errors).toHaveLength(0);
+    expect((schema.getType('Product') as GraphQLObjectType).getInterfaces())
+      .toHaveLength(2);
+
+    expect(printSchema(schema)).toContain('type Product implements Named & Node');
+    expect(composedSdl).toContain('type Product implements Named & Node');
+
+  });
 });
 
 describe('composition of schemas with directives', () => {
@@ -630,7 +708,7 @@ describe('composition of schemas with directives', () => {
   });
 
   it(`doesn't strip the special case @deprecated and @specifiedBy type-system directives`, () => {
-    const specUrl = "http://my-spec-url.com";
+    const specUrl = 'http://my-spec-url.com';
     const deprecationReason = "Don't remove me please";
 
     // Detecting >15.1.0 by the new addition of the `specifiedBy` directive
@@ -641,9 +719,11 @@ describe('composition of schemas with directives', () => {
       typeDefs: gql`
         # This directive needs to be conditionally added depending on the testing
         # environment's version of graphql (>= 15.1.0 includes this new directive)
-        ${isAtLeastGraphqlVersionFifteenPointOne
-          ? `scalar MyScalar @specifiedBy(url: "${specUrl}")`
-          : ''}
+        ${
+          isAtLeastGraphqlVersionFifteenPointOne
+            ? `scalar MyScalar @specifiedBy(url: "${specUrl}")`
+            : ''
+        }
 
         type EarthConcern {
           environmental: String!
@@ -673,7 +753,9 @@ describe('composition of schemas with directives', () => {
       const specifiedBy = schema.getDirective('specifiedBy');
       expect(specifiedBy).toMatchInlineSnapshot(`"@specifiedBy"`);
       const customScalar = schema.getType('MyScalar');
-      expect((customScalar as GraphQLScalarType).specifiedByUrl).toEqual(specUrl);
+      expect((customScalar as GraphQLScalarType).specifiedByUrl).toEqual(
+        specUrl,
+      );
     }
   });
 });

packages/apollo-federation/src/composition/compose.ts

@@ -16,6 +16,8 @@ import {
   TypeDefinitionNode,
   DirectiveDefinitionNode,
   TypeExtensionNode,
+  ObjectTypeDefinitionNode,
+  NamedTypeNode,
 } from 'graphql';
 import { transformSchema } from 'apollo-graphql';
 import federationDirectives from '../directives';
@@ -348,11 +350,55 @@ export function buildSchemaFromDefinitionsAndExtensions({
     directives: [...specifiedDirectives, ...federationDirectives],
   });
 
+  // This interface and predicate is a TS / graphql-js workaround for now while
+  // we're using a local graphql version < v15. This predicate _could_ be:
+  // `node is ObjectTypeDefinitionNode | InterfaceTypeDefinitionNode` in the
+  // future to be more semantic. However this gives us type safety and flexibility
+  // for now.
+  interface HasInterfaces {
+    interfaces?: ObjectTypeDefinitionNode['interfaces'];
+  }
+
+  function nodeHasInterfaces(node: any): node is HasInterfaces {
+    return 'interfaces' in node;
+  }
+
   // Extend the blank schema with the base type definitions (as an AST node)
   const definitionsDocument: DocumentNode = {
     kind: Kind.DOCUMENT,
     definitions: [
-      ...Object.values(typeDefinitionsMap).flat(),
+      ...Object.values(typeDefinitionsMap).flatMap(typeDefinitions => {
+        // See if any of our Objects or Interfaces implement any interfaces at all.
+        // If not, we can return early.
+        if (!typeDefinitions.some(nodeHasInterfaces)) return typeDefinitions;
+
+        const uniqueInterfaces: Map<
+          string,
+          NamedTypeNode
+        > = (typeDefinitions as HasInterfaces[]).reduce(
+          (map, objectTypeDef) => {
+            objectTypeDef.interfaces?.forEach((iface) =>
+              map.set(iface.name.value, iface),
+            );
+            return map;
+          },
+          new Map(),
+        );
+
+        // No interfaces, no aggregation - just return what we got.
+        if (uniqueInterfaces.size === 0) return typeDefinitions;
+
+        const [first, ...rest] = typeDefinitions;
+
+        return [
+          ...rest,
+          {
+            ...first,
+            interfaces: Array.from(uniqueInterfaces.values()),
+          },
+        ];
+
+      }),
       ...Object.values(directiveDefinitionsMap).map(
         definitions => Object.values(definitions)[0],
       ),