Typings fix and improvements.

[deskoh]

1. Fixed typings for Service.

- service<L extends keyof ServiceTypes> (location: L): ServiceTypes[L];
+ service<L extends keyof ServiceTypes> (location: L): Service<ServiceTypes[L]>;

2. Improvement in service typings is described as follows.

Current typings consists of a catch-all for any service name:

export interface Application<ServiceTypes = any> extends EventEmitter {

    service<L extends keyof ServiceTypes> (location: L): Service<ServiceTypes[L]>;

    // vvv: Catch-all for any service name
    service (location: string): Service<any>;
}

This allows service type to resolve if no ServiceType is specified.

const app = feathersExpress(feathers());
let service1 = app.service('messages'); // service1: Service<any>

However, if ServiceType is specified, invalid service name should not be resolved:

type Message = { text: string };
type App = Application<{ messages: Message }>;

const app2 = feathersExpress(feathers()) as App;
let service3 = app2.service('messages'); // service3: Service<Message>
let service4 = app2.service('message');  // service4: never <- Will resolve to Service<any> for current typings

Defaulting the ServiceType to {} and modifying the 'catch-all' typings can fulfill the above:

export interface Application<ServiceTypes = {}> extends EventEmitter {

    service<L extends keyof ServiceTypes> (location: L): Service<ServiceTypes[L]>;

    // vvv: Modified catch-all for service name if `ServiceType` is not provided
    service (location: string): keyof ServiceTypes extends never ? any : never;
}

[deskoh]

Expected type resolution:

let app: Application<{ users: User }>;
app.service('users'); // Service<User>
app.service('user');  // never

let app2: Application<any>;
app2.service('users'); // Service<any>
app2.service('user');  // Service<any>

let app3 = Application; // equivalent to Application<never>
app3.service('users'); // Service<any>
app3.service('user');  // Service<any>

[deskoh]

Test seems to fail due to the fix below:

-        service<L extends keyof ServiceTypes> (location: L): ServiceTypes[L];
+        service<L extends keyof ServiceTypes> (location: L): Service<ServiceTypes[L]>;

[daffl]

Thank you for the pull request. If someone just uses const app: Application without specifying the services mappings, it would still work (it'll just be returned as any) right?

[deskoh]

Yeap.

[daffl]

Great. Thanks again!