struct Fail: Error {}

func catcher(_ body: @autoclosure () throws -> Void) {}
func pitcher() throws {}

func audience(_ body: () throws -> Void) rethrows -> Void {}

func test1() {
  // This call doesn't throw.
  catcher(try pitcher())
}

func test2() {
  audience {
    // This is the same call, but this time it is evidently throwing.
    catcher(try pitcher())
  }
}

$ swift test.swift
test.swift:14:3: error: call can throw, but it is not marked with 'try' and the error is not handled
  audience {
  ^
test.swift:14:12: note: call is to 'rethrows' function, but argument function can throw
  audience {
           ^

func barrier<T>(_ body: () -> T) { body() }

func test3() {
  audience {
    barrier {
      catcher(try pitcher()) // OK
    }
  }
}