xwm: Handle WM_TRANSIENT_FOR

Set up X windows that are transient for another window as transient
surfaces in shell.c.  This keeps the transient windows on top of their
parent as windows are raised, lowered for fullscreened.

https://bugs.freedesktop.org/show_bug.cgi?id=69443

desktop-shell/shell.c

@@ -2127,6 +2127,10 @@ set_transient(struct shell_surface *shsurf,
 {
 	assert(parent != NULL);
 
+	shell_surface_set_parent(shsurf, parent);
+
+	surface_clear_next_states(shsurf);
+
 	shsurf->transient.x = x;
 	shsurf->transient.y = y;
 	shsurf->transient.flags = flags;
@@ -2149,9 +2153,6 @@ shell_surface_set_transient(struct wl_client *client,
 	struct weston_surface *parent =
 		wl_resource_get_user_data(parent_resource);
 
-	shell_surface_set_parent(shsurf, parent);
-
-	surface_clear_next_states(shsurf);
 	set_transient(shsurf, parent, x, y, flags);
 }
 

xwayland/window-manager.c

@@ -2179,6 +2179,7 @@ xserver_map_shell_surface(struct weston_wm *wm,
 	struct weston_shell_interface *shell_interface =
 		&wm->server->compositor->shell_interface;
 	struct weston_output *output;
+	struct weston_wm_window *parent;
 
 	if (!shell_interface->create_shell_surface)
 		return;
@@ -2208,14 +2209,19 @@ xserver_map_shell_surface(struct weston_wm *wm,
 		shell_interface->set_fullscreen(window->shsurf,
 						WL_SHELL_SURFACE_FULLSCREEN_METHOD_DEFAULT,
 						0, output);
-	} else if (!window->override_redirect && !window->transient_for) {
+	} else if (window->override_redirect) {
-		shell_interface->set_toplevel(window->shsurf);
-		return;
-	} else {
 		shell_interface->set_xwayland(window->shsurf,
 					      window->x,
 					      window->y,
 					      WL_SHELL_SURFACE_TRANSIENT_INACTIVE);
+	} else if (window->transient_for) {
+		parent = window->transient_for;
+		shell_interface->set_transient(window->shsurf,
+					       parent->surface,
+					       parent->x - window->x,
+					       parent->y - window->y, 0);
+	} else {
+		shell_interface->set_toplevel(window->shsurf);
 	}
 }