How to get a method return type with scala meta annotation?

I want do a Log annotation use scala meta.Usage simple as:

@Log
def f1(a: Int) {
    Future(a + 1) //result is a Future
}

// after parsed ====>
def f1(a: Int) {
    Future(a + 1).map{x => 
        println(x)
        x
    }
}

How can I check if f1 is a Future[ _ ] type? Thanks
Besides, I don't want use reflection(performance cost) in Log annotation and I think method result type can be decided at compile time.

Solution

This is not possible with scalameta macro annotations. The macro annotations are syntactic so they don't have access to semantic information such as types of trees.

PS. I am not sure if a macro annotation is suitable for this use-case, you could write out the log statement explicitly with something like this

def log[T](x: T): T = { println(x); x }
Future(1).map(log)

or even more concisely with an extension method

implicit class XtensionFuture[T](future: Future[T]) {
  def logged: Future[T] = future.map(log)
}
Future(1).logged

Macros should ideally be used as a last resort, not for convenience only.