[XWayland] Drag and Drop does not work in java -> wayland app direction

It is not possible to perform Drag and Drop in java -> wayland direction.

Root cause:

When we are trying perform DnD operation from XWayland to native Wayland window, it provides some dummy window under the cursor.

From my testing it is always has 0x600002 id:


$ xprop -id 0x600002
XdndAware(ATOM) = BITMAP

It has only XdndAware property and nothing else. But our code is picky when it is selecting the target window:

https://github.com/openjdk/jdk/blob/739769c8fc4b496f08a92225a12d07414537b6c0/src/java.desktop/unix/classes/sun/awt/X11/XDragSourceContextPeer.java#L399

https://github.com/openjdk/jdk/blob/739769c8fc4b496f08a92225a12d07414537b6c0/src/java.desktop/unix/classes/sun/awt/X11/XlibUtil.java#L318

It only accepts windows only with WM_STATE property set, so it prevents drag to initiate.

Accepting this window from Wayland allows to perform drop.