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[SR-15745] Actor methods able to be called from escaping closure without await #58022

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CharlesJS opened this issue Jan 17, 2022 · 1 comment
Closed

[SR-15745] Actor methods able to be called from escaping closure without await #58022

CharlesJS opened this issue Jan 17, 2022 · 1 comment
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async & await Feature → concurrency: asynchronous function aka the async/await pattern bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself concurrency Feature: umbrella label for concurrency language features diagnostics QoI Bug: Diagnostics Quality of Implementation not a bug Resolution → not a bug: Reported as a bug but turned out to be expected behavior or programmer error

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@CharlesJS
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Previous ID SR-15745
Radar rdar://90354322
Original Reporter @CharlesJS
Type Bug
Environment 
$ swiftc --version
swift-driver version: 1.26.21 Apple Swift version 5.5.2 (swiftlang-1300.0.47.5 clang-1300.0.29.30)
Target: x86_64-apple-macosx12.0
Additional Detail from JIRA
Votes 3
Component/s swift
Labels Bug
Assignee None
Priority Medium

md5: 581829c2432961ebf61e130142bf32e5

Issue Description:

This compiles, and I'm pretty sure it shouldn't:

import Dispatch

func someFunctionThatDoesWhoKnowsWhatWithThis(closure: @escaping () -> ()) {
  DispatchQueue.main.async { closure() }
}

class SomeClass {}

actor Foo {
  var bar = SomeClass()

  func setBar(_ bar: SomeClass) { self.bar = bar }
 
  func baz() {
    someFunctionThatDoesWhoKnowsWhatWithThis {
      self.setBar(.init()) // shouldn't this require an `await`?
    }
  }
}

The code inside the `@escaping` closure is no longer running inside the actor's context, so it seems like it shouldn't be able to call the actor's methods without an `await`, and that this is therefore a bug.

Forum thread with related discussion: https://forums.swift.org/t/calling-escaping-closure-from-actor-context-why-dont-i-need-await-here/51029
@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
@DougGregor
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As recently noted in the forum thread, this is an artifact of the compiler suppressing Sendable diagnostics in code that hasn't adopted concurrency. You can turn on completely checking manually with -Xfrontend -warn-concurrency (in Swift 5.6) or Swift 5.7's upcoming -strict-concurrency=complete. Doing so with my local Swift 5.7 build produces this:

t2.swift:4:30: warning: capture of 'closure' with non-sendable type '() -> ()' in a @Sendable closure
  DispatchQueue.main.async { closure() }
                             ^
t2.swift:4:30: note: a function type must be marked '@Sendable' to conform to 'Sendable'
  DispatchQueue.main.async { closure() }
                             ^

as it should.

@AnthonyLatsis AnthonyLatsis added concurrency Feature: umbrella label for concurrency language features compiler The Swift compiler in itself async & await Feature → concurrency: asynchronous function aka the async/await pattern not a bug Resolution → not a bug: Reported as a bug but turned out to be expected behavior or programmer error diagnostics QoI Bug: Diagnostics Quality of Implementation and removed swift labels Jan 16, 2023
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Labels
async & await Feature → concurrency: asynchronous function aka the async/await pattern bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself concurrency Feature: umbrella label for concurrency language features diagnostics QoI Bug: Diagnostics Quality of Implementation not a bug Resolution → not a bug: Reported as a bug but turned out to be expected behavior or programmer error
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@DougGregor @CharlesJS @AnthonyLatsis