duplicates:

• SR-9000 of deinitializers, property observers, and defer

Issue Description:

For the following code we produce a warning that the defer will be executed immediately:

class S {
  var foo = "" {
    didSet { print("didSet") }
  }

  deinit {
    // warning: 'defer' statement before end of scope always executes
    // immediately; replace with 'do' statement to silence this warning
    defer {
      foo = ""
    }
  }
}

The attached fix-it suggests replacing with a do statement, however that has the unfortunate consequence of changing the program's behaviour, as now the access to foo is done direct-to-storage and the property observer is no longer called. It's a shame that defer doesn't also perform a direct-to-storage access, but unfortunately quite a few people now rely on that behaviour.

Therefore I think we should limit this warning to only apply to contexts where property accesses are done normally, such as methods.

Interestingly enough, the warning already doesn't trigger on a defer that's the last statement of an initialiser, but I couldn't find specific logic that excludes this case. But even then, the exclusion isn't broad enough, as it doesn't cover the following case:

class S {
  var s = "" {
    didSet {
      print("didSet")
    }
  }

  init() {
    do {
      // warning: 'defer' statement before end of scope always executes
      // immediately; replace with 'do' statement to silence this warning
      defer {
        s = ""
      }
    }
  }
}