Fix FastifyInstance::ready type definition (#802)

* Fix FastifyInstance::ready type definition

* Add all FastifyInstance::ready() readyListener parameters possibilities definition

* Add FastifyInstance::ready() Promise usage ts defintion

* readyListener arg is not optional for callback usage of FastifyInstance::ready() ts definition

* Remove throw when callback is available on server ready types tests

fastify.d.ts

@@ -261,7 +261,10 @@ declare namespace fastify {
      * Registers a listener function that is invoked when all the plugins have
      * been loaded. It receives an error parameter if something went wrong.
      */
-    ready(readyListener?: () => void): void
+    ready(): Promise<FastifyInstance<HttpServer, HttpRequest, HttpResponse>>
+    ready(readyListener: (err: Error) => void): void
+    ready(readyListener: (err: Error, done: Function) => void): void
+    ready(readyListener: (err: Error, context: FastifyInstance<HttpServer, HttpRequest, HttpResponse>, done: Function) => void): void
 
     /**
      * Call this function to close the server instance and run the "onClose" callback

test/types/index.ts

@@ -251,3 +251,24 @@ server.setSchemaCompiler(function (schema: object) {
 server.addSchema({})
 
 server.printRoutes()
+
+server.ready(function (err) {
+  if (err) throw err
+})
+
+server.ready(function (err, done) {
+  done(err)
+})
+
+server.ready(function (err, context, done) {
+  server.log.debug(context)
+  done(err)
+})
+
+server.ready()
+  .then((context) => {
+    server.log.debug(context)
+  })
+  .catch((err) => {
+    server.log.error(err)
+  })