test/SILGen/polymorphic_inout_aliasing.swift

// RUN: %target-swift-emit-sil -verify %s

struct Block {}

class Story {
  final var finalStored = [Block]()
  var overridableStored = [Block]()
  var computed: [Block] {
    get { return [] }
    set {}
  }

  func test() {
    // expected-error@+2 {{overlapping accesses to 'finalStored', but modification requires exclusive access; consider calling MutableCollection.swapAt(_:_:)}}
    // expected-note@+1 {{conflicting access is here}}
    swap(&self.finalStored[0], &self.finalStored[1])
    swap(&self.overridableStored[0], &self.overridableStored[1])
    swap(&self.computed[0], &self.computed[1]) // expected-error{{invalid aliasing}} expected-note{{concurrent writeback}}
  }
}

protocol Storied {
  var protocolRequirement: [Block] { get set }
}

func testProtocol<T: Storied>(x: inout T) {
  // expected-error@+2 {{overlapping accesses to 'x', but modification requires exclusive access; consider calling MutableCollection.swapAt(_:_:)}}
  // expected-note@+1 {{conflicting access is here}}
  swap(&x.protocolRequirement[0], &x.protocolRequirement[1])
}