fix(schema): allow @canonical, @hidden, @renamed on FIELD_DEFINITION

The bundled directive declarations restricted @canonical, @hidden, and
@renamed to OBJECT only, causing local SDL validation to reject schemas
that apply them to fields. AWS's Merged API spec and best-practices
documentation explicitly support FIELD_DEFINITION usage, e.g.:

  rating: Int @canonical
  authorId: ID! @hidden
  getMessage(id: ID!): Message @renamed

Widen the location set to OBJECT | FIELD_DEFINITION.

Note: AWS's @renamed directive also takes a `to: String!` argument
(e.g. `@renamed(to: "newName")`). Adding it to this stub would break
existing users who write `@renamed` without an argument, so it is left
out of this change. See PR description for details.

Refs: https://aws.amazon.com/blogs/mobile/aws-appsync-merged-apis-best-practices-part-2-schema-composition/

Author: PatrykMilewski

src/__tests__/fixtures/schemas/merge-directives/schema.graphql

@@ -0,0 +1,20 @@
+type Query {
+  getUser(id: ID!): User! @canonical
+  internalUser(id: ID!): User! @hidden
+  legacyUser(id: ID!): User! @renamed
+}
+
+type User @canonical {
+  id: ID!
+  name: String! @canonical
+  email: String! @hidden
+  oldField: String @renamed
+}
+
+type Post @hidden {
+  id: ID!
+}
+
+type Comment @renamed {
+  id: ID!
+}

src/__tests__/schema.test.ts

@@ -153,6 +153,18 @@ describe('schema', () => {
     `);
   });
 
+  it('should accept merged-API directives on OBJECT and FIELD_DEFINITION', () => {
+    const api = new Api(
+      given.appSyncConfig({
+        schema: [
+          'src/__tests__/fixtures/schemas/merge-directives/schema.graphql',
+        ],
+      }),
+      plugin,
+    );
+    expect(() => api.compileSchema()).not.toThrow();
+  });
+
   it('should return single files schemas as-is', () => {
     const api = new Api(given.appSyncConfig(), plugin);
     const schema = new Schema(api, [

src/resources/Schema.ts

@@ -18,9 +18,9 @@ directive @aws_cognito_user_pools(
   cognito_groups: [String]
 ) on FIELD_DEFINITION | OBJECT
 directive @aws_subscribe(mutations: [String]) on FIELD_DEFINITION
-directive @canonical on OBJECT
-directive @hidden on OBJECT
-directive @renamed on OBJECT
+directive @canonical on OBJECT | FIELD_DEFINITION
+directive @hidden on OBJECT | FIELD_DEFINITION
+directive @renamed on OBJECT | FIELD_DEFINITION
 scalar AWSDate
 scalar AWSTime
 scalar AWSDateTime