Partly fix removal of systray from a wibox

This commit changes the systray widget, wibox.drawable and the C code to
fix the following bug: When the systray widget is removed from a
drawable without being moved somewhere else, the systray stayed visible.
This was because the systray is not drawn by awesome, but only placed.
When the widget is no longer "drawn", it stays wherever it was placed
last.

This change works by detecting the situation when the systray is
removed. Then, the C code is specifically told to remove the systray
window from the drawable.

Note that this is only a partial fix. This change works correctly when
the widget is removed completely, because it is no longer placed by its
parent widget. However, for example, when you do
wibox.widget.systray().visible = false, the effect is just that the
systray widget gets size 0x0. This is not really visible, but as far as
this change is concerned, the widget is still part of the drawable.

Signed-off-by: Uli Schlachter <psychon@znc.in>

lib/wibox/drawable.lua

@@ -25,6 +25,8 @@ local unpack = unpack or table.unpack -- luacheck: globals unpack (compatibility
 
 local visible_drawables = {}
 
+local systray_widget
+
 -- Get the widget context. This should always return the same table (if
 -- possible), so that our draw and fit caches can work efficiently.
 local function get_widget_context(self)
@@ -76,8 +78,15 @@ local function do_redraw(self)
     if self._need_relayout or self._need_complete_repaint then
         self._need_relayout = false
         if self._widget_hierarchy and self.widget then
+            local had_systray = systray_widget and self._widget_hierarchy:get_count(systray_widget) > 0
+
             self._widget_hierarchy:update(context,
                 self.widget, width, height, self._dirty_area)
+
+            local has_systray = systray_widget and self._widget_hierarchy:get_count(systray_widget) > 0
+            if had_systray and not has_systray then
+                systray_widget:_kickout(context)
+            end
         else
             self._need_complete_repaint = true
             if self.widget then
@@ -209,6 +218,11 @@ function drawable:find_widgets(x, y)
     return result
 end
 
+-- Private API. Not documented on purpose.
+function drawable._set_systray_widget(widget)
+    hierarchy.count_widget(widget)
+    systray_widget = widget
+end
 
 --- Set the widget that the drawable displays
 function drawable:set_widget(widget)

lib/wibox/widget/systray.lua

@@ -5,6 +5,7 @@
 ---------------------------------------------------------------------------
 
 local wbase = require("wibox.widget.base")
+local drawable = require("wibox.drawable")
 local beautiful = require("beautiful")
 local gtable = require("gears.table")
 local capi = {
@@ -72,6 +73,13 @@ function systray:draw(context, cr, width, height)
                          base, is_rotated, bg, reverse, spacing)
 end
 
+-- Private API. Does not appear in LDoc on purpose. This function is called
+-- some time after the systray is removed from some drawable. It's purpose is to
+-- really remove the systray.
+function systray:_kickout(context)
+    capi.awesome.systray(context.wibox.drawin)
+end
+
 function systray:fit(context, width, height)
     if not should_display_on(context.screen) then
         return 0, 0
@@ -171,6 +179,8 @@ local function new(revers)
         end
     end)
 
+    drawable._set_systray_widget(ret)
+
     return ret
 end
 

objects/drawin.c

@@ -166,6 +166,12 @@ drawin_systray_kickout(drawin_t *w)
     }
 }
 
+void
+luaA_drawin_systray_kickout(lua_State *L)
+{
+    drawin_systray_kickout(luaA_checkudata(L, 1, &drawin_class));
+}
+
 static void
 drawin_wipe(drawin_t *w)
 {

objects/drawin.h

@@ -47,8 +47,8 @@ struct drawin_t
 ARRAY_FUNCS(drawin_t *, drawin, DO_NOTHING)
 
 drawin_t * drawin_getbywin(xcb_window_t);
-
 void drawin_refresh_pixmap_partial(drawin_t *, int16_t, int16_t, uint16_t, uint16_t);
+void luaA_drawin_systray_kickout(lua_State *);
 
 void drawin_class_setup(lua_State *);
 

systray.c

@@ -337,7 +337,10 @@ luaA_systray(lua_State *L)
 {
     systray_register();
 
-    if(lua_gettop(L) != 0)
+    if(lua_gettop(L) == 1)
+        luaA_drawin_systray_kickout(L);
+
+    if(lua_gettop(L) > 1)
     {
         size_t bg_len;
         drawin_t *w = luaA_checkudata(L, 1, &drawin_class);