widget: Add recursive signals.

This allows to ignore containers and layouts when a signal is sent.

docs/common/widget.ldoc

@@ -40,6 +40,13 @@
 -- @param _buttons The table of buttons that should bind to the widget.
 -- @function buttons
 
+--- Emit a signal and ensure all parent widgets in the hierarchies also
+-- forward the signal. This is useful to track signals when there is a dynamic
+-- set of containers and layouts wrapping the widget.
+-- @tparam string signal_name
+-- @param ... Other arguments
+-- @function emit_signal_recursive
+
 --- When the layout (size) change.
 -- This signal is emited when the previous results of `:layout()` and `:fit()`
 -- are no longer valid.

lib/wibox/hierarchy.lua

@@ -51,6 +51,16 @@ local function hierarchy_new(redraw_callback, layout_callback, callback_arg)
         end
         layout_callback(result, callback_arg)
     end
+    function result._emit_recursive(widget, name, ...)
+        local cur = result
+        assert(widget == cur._widget)
+        while cur do
+            if cur._widget then
+                cur._widget:emit_signal(name, ...)
+            end
+            cur = cur._parent
+        end
+    end
 
     for k, f in pairs(hierarchy) do
         if type(f) == "function" then
@@ -86,6 +96,7 @@ function hierarchy_update(self, context, widget, width, height, region, matrix_t
     if old_widget and old_widget ~= widget then
         self._widget:disconnect_signal("widget::redraw_needed", self._redraw)
         self._widget:disconnect_signal("widget::layout_changed", self._layout)
+        self._widget:disconnect_signal("widget::emit_recursive", self._emit_recursive)
     end
 
     -- Save the arguments we need to save
@@ -99,6 +110,7 @@ function hierarchy_update(self, context, widget, width, height, region, matrix_t
     if old_widget ~= widget then
         widget:weak_connect_signal("widget::redraw_needed", self._redraw)
         widget:weak_connect_signal("widget::layout_changed", self._layout)
+        widget:weak_connect_signal("widget::emit_recursive", self._emit_recursive)
     end
 
     -- Update children

lib/wibox/widget/base.lua

@@ -153,6 +153,27 @@ function base.widget:get_all_children()
     return ret
 end
 
+--- Emit a signal and ensure all parent widgets in the hierarchies also
+-- forward the signal. This is useful to track signals when there is a dynamic
+-- set of containers and layouts wrapping the widget.
+--
+-- Note that this function has two flaws. First of all, the signal are only
+-- forwarded once the widget tree has been built. This happens after all
+-- currently scheduled functions have been executed. Therefor, it wont start
+-- to work right away. In case the widget is present multiple time in a single
+-- widget tree, this function will also forward the signal multiple time (one
+-- per upward tree path).
+--
+-- @tparam string signal_name
+-- @param ... Other arguments
+-- @function emit_signal_recursive
+function base.widget:emit_signal_recursive(signal_name, ...)
+    -- This is a convenience wrapper, the real implementation is in the
+    -- hierarchy.
+
+    self:emit_signal("widget::emit_recursive", signal_name, ...)
+end
+
 --- Get a widex index.
 -- @param widget The widget to look for
 -- @param[opt] recursive Also check sub-widgets