An odd error: "Escaping closure captures mutating 'self'"

[Peter-Schorn]

@Jens

func test(_ a: () -> Void) {
  let b = { print("b") }
  let x = Bool.random() ? a : b
  x()
}

What a bizzare bug. Interestingly, if you mark the closure as escaping—even though it doesn't escape—then it compiles again. I suggest adding this to the report.