Fix errorFormatter's TypeScript typing. (#255)

* Fix errorFormatter's TypeScript typing.

* It looks like statusCode should be required too.

* Add errorFormatter to the types test.

index.d.ts

@@ -160,13 +160,11 @@ export interface FastifyGQLCommonOptions {
    * Change the default error formatter.
    */
   errorFormatter?: ((
-    error: FastifyError | GraphQLError | Error
+    execution: ExecutionResult,
+    context: any,
   ) => {
-    statusCode?: number
-    response?: {
-      data?: object
-      errors: any[]
-    }
+    statusCode: number,
+    response: ExecutionResult,
   });
   /**
    * The maximum depth allowed for a single query.

test/types/index.ts

@@ -54,6 +54,11 @@ app.register(fastifyGQL, {
   prefix: '/prefix',
   defineMutation: false,
   errorHandler: true,
+  errorFormatter: (result, context) => {
+    result.data
+    result.errors?.forEach(e => e.message)
+    return { statusCode: 200, response: result }
+  },
   queryDepth: 8,
   cache: true
 })