Linux with Wayland and Java 21: popups that request focus are not shown

[DevCharly]

On Linux with Wayland, since Java 21, Swing adds a window focus listener
to popup owner/invoker window, which hides the popup as soon as the owner window looses focus.
This works fine for light-weight popups (because they use JPanel).
It also works for heavy-weight popups (which use JWindow) if the do not request focus (e.g. menus, tooltips, combobox list).
Because FlatLaf always uses heavy-weight popups, all popups that request focus are broken since Java 21.

JDK bug and PR that cause the problem:

• https://bugs.openjdk.org/browse/JDK-8280993
• 8280993: [XWayland] Popup is not closed on click outside of area controlled by XWayland openjdk/jdk#13830

Test case to reproduce the issue:

import java.awt.*;
import javax.swing.*;
import javax.swing.event.*;
import com.formdev.flatlaf.FlatLightLaf;

public class LinuxWaylandJava21PopupTest
{
    public static void main( String[] args ) {
        SwingUtilities.invokeLater( () -> {
            FlatLightLaf.setup();
            JFrame frame = new JFrame( LinuxWaylandJava21PopupTest.class.getSimpleName() );
            frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );

            JButton showPopup = new JButton( "show popup" );
            showPopup.addActionListener( e -> {
                JPanel popupPanel = new JPanel();
                popupPanel.add( new JTextField( 20 ) );

                JPopupMenu popupMenu = new JPopupMenu();
                popupMenu.add( popupPanel );
                popupMenu.addPopupMenuListener( new PopupMenuListener() {
                    @Override
                    public void popupMenuWillBecomeVisible( PopupMenuEvent e ) {
                        EventQueue.invokeLater( () -> {
                            // focus first component in popup
                            popupPanel.transferFocus();
                        } );
                    }
                    @Override
                    public void popupMenuWillBecomeInvisible( PopupMenuEvent e ) {
                        System.out.println( "popup will become invisible" );
                    }
                    @Override
                    public void popupMenuCanceled( PopupMenuEvent e ) {
                        System.out.println( "popup canceled" );
                    }
                } );
                popupMenu.show( showPopup, 0, showPopup.getHeight() );
            } );
            frame.add( showPopup );

            frame.add( new JLabel( "Java version " + System.getProperty( "java.version" ) ), BorderLayout.NORTH );
            frame.pack();
            frame.setVisible( true );
        } );
    }
}

[DevCharly]

fixed in 3.2.3