Prevent parsing schema exceptions when importing directives (#900)

* Prevent parsing schema extensions

* Add unit test

lib/federation.js

@@ -92,7 +92,7 @@ function getStubTypes (schemaDefinitions, isGateway) {
   const directiveDefinitions = []
 
   for (const definition of schemaDefinitions) {
-    if (definition.kind === 'SchemaDefinition') {
+    if (definition.kind === 'SchemaDefinition' || definition.kind === 'SchemaExtension') {
       continue
     }
 

test/federation.js

@@ -1087,3 +1087,45 @@ test('basic federation support with \'schema\' in the schema', async (t) => {
     }
   })
 })
+
+test('should support directives import syntax', async (t) => {
+  const app = Fastify()
+
+  const schema = `
+    extend schema
+      @link(url: "https://specs.apollo.dev/federation/v2.0",
+        import: ["@key", "@shareable", "@override"])
+
+    extend type Query {
+      hello: String
+    }
+  `
+
+  const resolvers = {
+    Query: {
+      hello: () => 'world'
+    }
+  }
+
+  app.register(GQL, {
+    schema,
+    resolvers,
+    federationMetadata: true
+  })
+
+  await app.ready()
+
+  const query = '{ _service { sdl } }'
+  const res = await app.inject({
+    method: 'GET',
+    url: `/graphql?query=${query}`
+  })
+
+  t.same(JSON.parse(res.body), {
+    data: {
+      _service: {
+        sdl: schema
+      }
+    }
+  })
+})