dispatch_inference.swift

// RUN: %target-swift-frontend -target %target-swift-5.1-abi-triple %import-libdispatch -strict-concurrency=complete %s -emit-sil -o /dev/null -verify -strict-concurrency=targeted
// RUN: %target-swift-frontend -target %target-swift-5.1-abi-triple %import-libdispatch -strict-concurrency=complete %s -emit-sil -o /dev/null -verify -verify-additional-prefix tns-

// REQUIRES: concurrency
// REQUIRES: libdispatch

import Dispatch

// Tests the inference of @_unsafeSendable and @MainActor when working with
// the Dispatch library, and specifically, DispatchQueue.
@MainActorfunc onlyOnMainActor(){}

func testMe(){
DispatchQueue.main.async{
onlyOnMainActor() // okay, due to inference of @MainActor-ness
}

DispatchQueue.main.sync{
onlyOnMainActor()
}
}

func testUnsafeSendableInMainAsync()async{
varx=5
DispatchQueue.main.async{
 x =17 // expected-warning{{mutation of captured var 'x' in concurrently-executing code}}
 // expected-tns-warning @-1 {{sending 'x' risks causing data races}}
 // expected-tns-note @-2 {{'x' is captured by a main actor-isolated closure. main actor-isolated uses in closure may race against later nonisolated uses}}
}
print(x) // expected-tns-note {{access can happen concurrently}}
}

func testUnsafeSendableInAsync(queue:DispatchQueue)async{
varx=5
 queue.async{
 x =17 // expected-warning{{mutation of captured var 'x' in concurrently-executing code}}
}

 queue.sync{
 x =17 // okay
}

print(x)
}