[Request] Add Synchronous Call Adapter

[jaredsburrows]

Problem:

From Retrofit 1:

interface Service {
   String someRequest();
}

For Retrofit 2, we are forced to use Call or some other call adapter such as Observable with RxJava/2 call adapters.

Question:

See http://stackoverflow.com/a/35104080, can we add a synchronous call adapter?

[JakeWharton]

We very explicitly don't support this by default. Call was designed so that the interface could remain constant while allowing both synchronous and asynchronous invocation without needing the interface to change.

As the StackOverflow answer indicates, it's fairly easy to write your own adapter that provides the legacy behavior, although you miss out on things like the ability to cancel, see headers, get the error body, etc. These deficiencies plagued 1.x which is why we actively steer you away from it in 2.x.