False positive warning about closure isolation but only when argument label is omitted

[groue]

Description

The compiler changes its diagnostic depending on whether a closure argument is declared with or without argument label.

Reproduction

struct SUT {
    func run1(completion: sending @escaping () -> Void) { }
    func run2(_ completion: sending @escaping () -> Void) { }
}

@MainActor
func test_run() {
    let sut = SUT()

    // No warning
    sut.run1 { }

    // Main actor-isolated value of type '() -> ()' passed as a strongly
    // transferred parameter; later accesses could race
    sut.run2 { }
}

This is very confusing.

Expected behavior

No warning in both cases.

Environment

% swiftc -version
swift-driver version: 1.112.3 Apple Swift version 6.0 (swiftlang-6.0.0.6.8 clang-1600.0.23.1)
Target: arm64-apple-macosx14.0

Additional information

No response

[groue]

Related: #75521

[gottesmm]

@groue so this doesn't reproduce on main anymore. It was fixed in

tags/swift-DEVELOPMENT-SNAPSHOT-2024-08-28-a..tags/swift-DEVELOPMENT-SNAPSHOT-2024-08-29-a.

So one of these commits:

406b8bd Merge pull request #76133 from slavapestov/sync-local-func-isolation
543fd21 Merge pull request #76125 from ian-twilightcoder/unknown-platform-attr
8503f72 Merge pull request #76111 from tshortli/lazy-typecheck-lazy-var-in-inlinable-func
dfa60a1 Merge pull request #76101 from kateinoigakukun/yt/update-swift-collection-113
3436c49 Merge pull request #76123 from hamishknight/a-form-of-expression
6465bdc Merge pull request #76042 from xedin/rdar-133415157
00eee36 Merge pull request #76115 from xedin/rdar-131524246

[groue]

Thank you @gottesmm :-) Glad the bug is fixed in the latest snapshot, because it is still there in Xcode 16.1 beta 3. #75521 is a similar issue.

[gottesmm]

This is fixed in the 6.1 release.