Non-determinist signature results in TS2349

[gjuchault]

TypeScript Version:

1.8.10

Code

Failure:

this.loginService.loginUser(user, pass)
  .subscribe(
    payload => {
      this.storageService.put('accesstoken', payload.token);
      this.storageService.put('guid', payload.guid);
      return this.loginService.fetchUserName(payload);
    },
    error => this.handleError(error)
  );

Working:

const login: Observable<any> = this.loginService.loginUser(user, pass);

login.subscribe(
    payload => {
      this.storageService.put('accesstoken', payload.token);
      this.storageService.put('guid', payload.guid);
      return this.loginService.fetchUserName(payload);
    },
    error => this.handleError(error)
  );

Definition for loginUser:

public loginUser(userName: string, password: string): Observable<LoginResponse> | Observable<Error>

Expected behavior:

No errors

Actual behavior:

TS2349: Cannot invoke an expression whose type lacks a call signature.

Notes
It comes from the | operator in the loginUser function. If I switch to a "determinist" type by putting Observable<any>, typescript is some way "sure" (sorry for the term) of having an observable and it accepts the subscribe call.

[Arnavion]

See #4612