Incorrect data race diagnostic when capturing weak reference to actor-isolated class via a non-isolated context #85402
Description
Description
The following snippet compiles successfully using Swift 6.2 but fails to compile with the most recent main snapshot.
A reference to a MainActor isolated instance is first weakly captured in a non-isolated closure. Then that weak reference is captured in a MainActor isolated closure but the compiler erroneously won't allow accessing it there.
No error when capturing a strong reference or turning the weak ref into a strong one before capturing it in the inner, isolated, closure.
Reproduction
// Compile with: swiftc -swift-version 6
func notIsolated(_: @Sendable () -> Void) {}
func onMainActor(_: @MainActor () -> Void) {}
@MainActor
final class IsolatedClass {
func foo() {
notIsolated { [weak self] in
onMainActor {
// error: sending 'self' risks causing data races [#SendingRisksDataRace]
_ = self
}
}
}
}Expected behavior
Compiles successfully
Environment
main-snapshot-2025-11-03 installed via swiftly
Apple Swift version 6.3-dev (LLVM bff1370bd79c983, Swift 57cf4ce)
Additional information
No response