types: nullish error types in callback function's parameter for `afte…

…r` and `ready` method (#5191)

* types: nullish error types in callback function's parameter

* types: update `ready` method's parameter type

Co-authored-by: KaKa <23028015+climba03003@users.noreply.github.com>

* types: add tests for `after` & `ready` methods

---------

Co-authored-by: KaKa <23028015+climba03003@users.noreply.github.com>

test/types/instance.test-d.ts

@@ -256,6 +256,18 @@ expectNotDeprecated(server.listen({ port: 3000, host: '0.0.0.0', backlog: 42 },
 expectNotDeprecated(server.listen({ port: 3000, host: '0.0.0.0', backlog: 42, exclusive: true }, () => {}))
 expectNotDeprecated(server.listen({ port: 3000, host: '::/0', ipv6Only: true }, () => {}))
 
+// test after method
+expectAssignable<FastifyInstance>(server.after())
+expectAssignable<FastifyInstance>(server.after((err) => {
+  expectType<Error | null>(err)
+}))
+
+// test ready method
+expectAssignable<FastifyInstance>(server.ready())
+expectAssignable<FastifyInstance>(server.ready((err) => {
+  expectType<Error | null>(err)
+}))
+
 expectAssignable<void>(server.routing({} as RawRequestDefaultExpression, {} as RawReplyDefaultExpression))
 
 expectType<FastifyInstance>(fastify().get<RouteGenericInterface, { contextKey: string }>('/', {

types/instance.d.ts

@@ -137,7 +137,7 @@ export interface FastifyInstance<
   getSchemas(): Record<string, unknown>;
 
   after(): FastifyInstance<RawServer, RawRequest, RawReply, Logger, TypeProvider> & PromiseLike<undefined>;
-  after(afterListener: (err: Error) => void): FastifyInstance<RawServer, RawRequest, RawReply, Logger, TypeProvider>;
+  after(afterListener: (err: Error | null) => void): FastifyInstance<RawServer, RawRequest, RawReply, Logger, TypeProvider>;
 
   close(): Promise<undefined>;
   close(closeListener: () => void): undefined;
@@ -190,7 +190,7 @@ export interface FastifyInstance<
   listen(port: number | string, address?: string, backlog?: number): Promise<string>;
 
   ready(): FastifyInstance<RawServer, RawRequest, RawReply, Logger, TypeProvider> & PromiseLike<undefined>;
-  ready(readyListener: (err: Error) => void): FastifyInstance<RawServer, RawRequest, RawReply, Logger, TypeProvider>;
+  ready(readyListener: (err: Error | null) => void): FastifyInstance<RawServer, RawRequest, RawReply, Logger, TypeProvider>;
 
   register: FastifyRegister<FastifyInstance<RawServer, RawRequest, RawReply, Logger, TypeProvider> & PromiseLike<undefined>>;