Fix to allow extended properties in federated schema with custom directives

lib/index.js

@@ -3,7 +3,7 @@
 const graphql = require('graphql');
 const gql = require('graphql-tag');
 const { buildFederatedSchema } = require('@apollo/federation');
-const { makeExecutableSchema, addMockFunctionsToSchema, mergeSchemas } = require('graphql-tools');
+const { makeExecutableSchema, addMockFunctionsToSchema, SchemaDirectiveVisitor } = require('graphql-tools');
 const { mergeResolvers, mergeTypeDefs } = require('graphql-toolkit');
 const { getImportedResolvers, transformResolvers, wrapResolvers } = require('./resolvers');
 const { wrapContext, createContext } = require('./context');
@@ -108,7 +108,7 @@ class GraphQLComponent {
 
   execute(input, { root = undefined, context = {}, variables = {} } = {}) {
     const document = typeof input === 'string' ? gql`${this._fragments.join('\n')}\n${input}` : input;
-    
+
     return graphql.execute({ document, schema: this.schema, rootValue: root, contextValue: context, variableValues: variables });
   }
 
@@ -118,12 +118,13 @@ class GraphQLComponent {
       resolvers
     });
 
-    return mergeSchemas({
-      schemas: [federatedSchema],
-      schemaDirectives,
-      mergeDirectives: true
-    });
-  } 
+    // Add any custom schema directives
+    if (schemaDirectives) {
+      SchemaDirectiveVisitor.visitSchemaDirectives(federatedSchema, schemaDirectives);
+    }
+
+    return federatedSchema;
+  }
 
   get schema() {
     if (this._schema) {

test/test-federation.js

@@ -25,6 +25,10 @@ Test('federated schema', (t) => {
         id: ID!
         geo: [String]
       }
+      extend type Extended @key(fields: "id") {
+        id: ID! @external
+        newProp: String
+      }
       `
     ],
     resolvers: {
@@ -38,7 +42,7 @@ Test('federated schema', (t) => {
       },
       Property: {
         __resolveReference(property, context) {
-          
+
         }
       }
     },
@@ -58,4 +62,11 @@ Test('federated schema', (t) => {
     const {schema: {_directives: schemaDirectives}} = component;
     t.equals(schemaDirectives.filter((directive) => directive.name === 'custom').length, 1, `federated schema has '@custom' directive`);
   });
+
+  t.test('extended properties maintained after adding custom directive', (t) => {
+    t.plan(2);
+    const {schema: {_typeMap: {Extended}}} = component;
+    t.equals(Extended.extensionASTNodes.length, 1, 'Extension AST Nodes is defined');
+    t.equals(Extended.extensionASTNodes[0].fields.filter((field) => field.name.value === "id" && field.directives[0].name.value === "external").length, 1, `id field marked external`);
+  });
 });