`Cannot rewrite recursive call: it is not in tail position` error

[xuwei-k]

Compiler version

• 3.1.2-RC1-bin-20211102-82172ed-NIGHTLY
• 3.1.1-RC1
• 3.1.0
• 3.0.2

Minimized code

import scala.annotation.tailrec

class A {
  def b = Option("a").map { x =>
    @tailrec def loop(): Int = {
      try {
        2
      } catch { 
        case _: Throwable =>
          loop()
      }
    }
    x
  }
}

Output

[error] 10 |          loop()
[error]    |          ^^^^^^
[error]    |          Cannot rewrite recursive call: it is not in tail position

Expectation

[nicolasstucki]

Even worse, with the following variant the check passes and the tailrec transformation is ignored

import scala.annotation.tailrec

class A {
  def b = Option("a").map { x =>
    def loop(): Int = {
      try {
        loop()
      } catch {
        case _: Throwable =>
          2
      }
    }
    x
  }
}

[bishabosha]

Even worse, with the following variant the check passes and the tailrec transformation is ignored

I think there may be a typo - it fails for me when I annotated loop as tailrec

[nicolasstucki]

Indeed. My mistake.

[KacperFKorban]

The problem here is that LiftTry is applied for the try-catch statement and this makes it no longer directly tailrec. I drafted a PR, but after some consideration, I'm not sure if it is correct.