window-props: Don't set override redirect windows as top-level parent

Java applications might use override-redirect windows as parent windows for
top-level windows, although this is not following the standard [1].

In such case, the first non-override-redirect child window that is created
was marked as being on_all_workspaces since the call to
should_be_on_all_workspaces() returns TRUE for its parent, and this even
though the on_all_workspaces_requested bit is unset.
When a further child of this window was added, it was set as not having a
workspace and not being on_all_workspaces, since the call to
should_be_on_all_workspaces() for its parent would return FALSE (unless if
it is in a different monitor, and the multiple-monitors workspaces are
disabled).

Since per commit 09bab98b we don't recompute the workspace if the
on_all_workspaces bit is unset, we could end up in a case where a window can
be nor in all the workspaces or in a specific workspace.

So let's just ignore the transient_for bit for a window if that points to an
override-redirect, using the x11 root window instead.

Add a stacking test to verify this scenario (was failing before of this
commit).

Fixes https://gitlab.gnome.org/GNOME/mutter/issues/885
https://gitlab.gnome.org/GNOME/mutter/merge_requests/895

[1] https://standards.freedesktop.org/wm-spec/wm-spec-latest.html#idm140200472512128

src/tests/meson.build

@@ -131,6 +131,7 @@ stacking_tests = [
   'mixed-windows',
   'set-parent',
   'override-redirect',
+  'set-override-redirect-parent',
   'set-parent-exported',
 ]
 

src/tests/stacking/set-override-redirect-parent.metatest

@@ -0,0 +1,24 @@
+new_client 1 x11
+create 1/1 override
+show 1/1
+
+create 1/2
+set_parent 1/2 1
+show 1/2
+
+create 1/3
+set_parent 1/3 2
+show 1/3
+
+
+new_client 2 x11
+create 2/1
+show 2/1
+
+create 2/2 override
+set_parent 2/2 1
+show 2/2
+
+create 2/3
+set_parent 2/3 2
+show 2/3

src/x11/window-props.c

@@ -1661,6 +1661,15 @@ reload_transient_for (MetaWindow    *window,
                         transient_for, window->desc);
           transient_for = None;
         }
+      else if (parent->override_redirect)
+        {
+          meta_warning ("WM_TRANSIENT_FOR window %s for top-level %s is an "
+                        "override-redirect window and this is not correct "
+                        "according to the standard, so we'll fallback to "
+                        "the root window.\n", parent->desc, window->desc);
+          transient_for = parent->display->x11_display->xroot;
+          parent = NULL;
+        }
 
       /* Make sure there is not a loop */
       if (check_xtransient_for_loop (window, parent))