Tor Arne Vestbø 2e63759c1b Don't run the AppKit run loop nested in Swift's async main (#1260) ...

When built against the macOS 27 (Xcode 27, Swift 6.4) SDK, "tart run"
brings up the VM window but the guest never boots.

Swift's asynchronous main() entry point implicitly starts an executor
that owns the main thread, and as of Swift 6.4 that executor is no
longer backed by the Dispatch main queue. Running an AppKit/SwiftUI
run loop nested inside it via MainApp.main() leaves the main run loop
unable to drain Swift tasks or DispatchQueue.main, so the task that
starts the VM is never scheduled, even though the window itself
(driven directly by AppKit during launch) still appears.

We now keep Root.main() synchronous, so that a command driving a run
loop can own the main thread at the top level, exactly like a plain
SwiftUI app. With AppKit owning the loop again, MainActor tasks and
the Dispatch main queue drain as before. Such commands opt in through
a new MainThreadCommand protocol; everything else keeps running
asynchronously via a detached task and dispatchMain().

Verified that the guest boots again, and that Ctrl+C still stops the
VM gracefully.

2026-06-09 09:53:06 -07:00

..

tart

Don't run the AppKit run loop nested in Swift's async main (#1260)

2026-06-09 09:53:06 -07:00