Cocoa: Make sure we can display multiple sheets for the same NSWindow

On macOS, to display a modal with Qt::WindowModality set, or of type
Qt::Sheet, we call beginSheet:completinHandler:. However, this method
won't display the specified sheet unless the current active one is
dismissed, which is a different behavior than what we expect for
this case. Use beginCriticalSheet:completionHandler: whenever we
already have an active sheet attached to the NSWindow, which allows
us to display multiple sheets for the same window.

Fixes: QTBUG-91059
Pick-to: 5.15 6.1 6.2
Change-Id: I86bdbcbd63758edbbc48a8aade0178917dcb0e5b
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

1 files changed, 5 insertions, 1 deletions

diff --git a/src/plugins/platforms/cocoa/qcocoawindow.mm b/src/plugins/platforms/cocoa/qcocoawindow.mm
index dcf65e9fa8..d4c1593936 100644
--- a/src/plugins/platforms/cocoa/qcocoawindow.mm
+++ b/src/plugins/platforms/cocoa/qcocoawindow.mm
@@ -368,7 +368,11 @@ void QCocoaWindow::setVisible(bool visible)
             if (window()->windowState() != Qt::WindowMinimized) {
                 if (parentCocoaWindow && (window()->modality() == Qt::WindowModal || window()->type() == Qt::Sheet)) {
                     // Show the window as a sheet
-                    [parentCocoaWindow->nativeWindow() beginSheet:m_view.window completionHandler:nil];
+                    NSWindow *nativeParentWindow = parentCocoaWindow->nativeWindow();
+                    if (!nativeParentWindow.attachedSheet)
+                        [nativeParentWindow beginSheet:m_view.window completionHandler:nil];
+                    else
+                        [nativeParentWindow beginCriticalSheet:m_view.window completionHandler:nil];
                 } else if (window()->modality() == Qt::ApplicationModal) {
                     // Show the window as application modal
                     eventDispatcher()->beginModalSession(window());