[5.9] [Changelog] Add changelog entry for SE-0380

[hamishknight]

5.9 cherry-pick of #65887

SE-0380

[hamishknight]

@swift-ci please test

[altairdeark]

Hi @hamishknight , i am facing an issue with SE-0380 and latest xcode Beta. Now Return have unexpected behavior in case if if or switch used after it.

Compilable

func test() {
          print('1')
          return /// expect the end of progamm here

          if true {
               print('2') /// still will be executable, bcs `if` now is equal to `()`
          } else {
               print('3')
          }

          return
}

Result:

1
2

2 is unexpected

I believe Swift update should complement rather than break the existing one. Is it a known issue?

[hamishknight]

@altairdeark This is expected, see https://github.com/apple/swift-evolution/blob/main/proposals/0380-if-switch-expressions.md#source-compatibility:

As proposed, this addition has one source incompatibility, related to unreachable code. The following currently compiles, albeit with a warning that the if statement is unreachable (and the values in the branches unused):

func foo() {
  return
  if .random() { 0 } else { 0 }
}

The code provided produces the following warning:

func test() {
  print("1")
  return

  if true { // warning: expression following 'return' is treated as an argument of the 'return'
    print("2")
  } else {
    print("3")
  }

  return
}

[altairdeark]

@hamishknight ,

Still it is breaks the old code, and not everyone will recheck whole code base to fix this warning, since in older project i have 1000+ warnings (legacy). In my case in if i was having an unexpected server API calls which was a total surprise for me since i was not aware of SE-0380. I believe it could also breaks others project, libs and else.

Do we have any option to solve it? like: when after return we have a new line or \r, so it should not treat If as an argument for return and just behave as it was.

[hamishknight]

@altairdeark You can add a ; to the end of the return to avoid treating the following expression as part of the return