Upgrade to newer apollo-server-types which declares info.cacheControl

Also do some other code review feedback.

federation-js/package.json

@@ -24,7 +24,7 @@
   },
   "dependencies": {
     "apollo-graphql": "^0.9.3",
-    "apollo-server-types": "^3.0.0",
+    "apollo-server-types": "^3.0.2",
     "lodash.xorby": "^4.7.0"
   },
   "peerDependencies": {

federation-js/src/types.ts

@@ -13,17 +13,7 @@ import {
   isObjectType,
 } from 'graphql';
 import { PromiseOrValue } from 'graphql/jsutils/PromiseOrValue';
-import { CacheHint, CachePolicy } from 'apollo-server-types';
-
-declare module 'graphql/type/definition' {
-  interface GraphQLResolveInfo {
-    cacheControl: {
-      cacheHint: CachePolicy;
-      setCacheHint(hint: CacheHint): void;
-      cacheHintFromType(t: GraphQLCompositeType): CacheHint | undefined;
-    };
-  }
-}
+import { CacheHint } from 'apollo-server-types';
 
 export const EntityType = new GraphQLUnionType({
   name: '_Entity',
@@ -98,11 +88,15 @@ export const entitiesField: GraphQLFieldConfig<any, any> = {
         );
       }
 
+      // Note that while our TypeScript types (as of apollo-server-types@3.0.2)
+      // tell us that cacheControl and restrict are always defined, we want to
+      // avoid throwing when used with Apollo Server 2 which doesn't have
+      // `restrict`, or if the cache control plugin has been disabled.
       if (info.cacheControl?.cacheHint?.restrict) {
         const cacheHint: CacheHint | undefined =
           info.cacheControl.cacheHintFromType(type);
 
-        if (cacheHint?.maxAge || cacheHint?.scope) {
+        if (cacheHint) {
           info.cacheControl.cacheHint.restrict(cacheHint);
         }
       }