Implement :set_children() sanely everywhere

This makes the code use the existing functions for setting widgets. That way,
all the sanity checks that the existing functions have are applied for this code
as well.

I just spent half an hour tracking down a bug where a boolean ended up as a
"widget" in a fixed layout. The symptom was that while drawing the widget, an
error happened. Via this change, the error would instead be flagged while
constructing the widget.

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

lib/wibox/layout/align.lua

@@ -175,11 +175,9 @@ end
 -- This layout only accept three children, all others will be ignored
 -- @tparam table children A table composed of valid widgets
 function align:set_children(children)
-    if not children then return self:reset() end
-    self.first  = children[1]
-    self.second = children[2]
-    self.third  = children[3]
-    self:emit_signal("widget::layout_changed")
+    self:set_first(children[1])
+    self:set_second(children[2])
+    self:set_third(children[3])
 end
 
 --- Fit the align layout into the given space. The align layout will

lib/wibox/layout/constraint.lua

@@ -54,8 +54,7 @@ end
 -- This layout only accept one children, all others will be ignored
 -- @tparam table children A table composed of valid widgets
 function constraint:set_children(children)
-    self.widget = children and children[1]
-    self:emit_signal("widget::layout_changed")
+    self:set_widget(children[1])
 end
 
 --- Set the strategy to use for the constraining. Valid values are 'max',

lib/wibox/layout/fixed.lua

@@ -5,6 +5,7 @@
 -- @classmod wibox.layout.fixed
 ---------------------------------------------------------------------------
 
+local unpack = unpack or table.unpack -- luacheck: globals unpack (compatibility with Lua 5.1)
 local base  = require("wibox.widget.base")
 local table = table
 local pairs = pairs
@@ -110,9 +111,10 @@ end
 --- Replace the layout children
 -- @tparam table children A table composed of valid widgets
 function fixed:set_children(children)
-    if not children then return self:reset() end
-    self.widgets = children
-    self:emit_signal("widget::layout_changed")
+    self:reset()
+    if #children > 0 then
+        self:add(unpack(children))
+    end
 end
 
 --- Replace the first instance of `widget` in the layout with `widget2`

lib/wibox/layout/margin.lua

@@ -82,8 +82,7 @@ end
 -- This layout only accept one children, all others will be ignored
 -- @tparam table children A table composed of valid widgets
 function margin:set_children(children)
-    self.widget = children and children[1]
-    self:emit_signal("widget::layout_changed")
+    self:set_widget(children[1])
 end
 
 --- Set all the margins to val.

lib/wibox/layout/mirror.lua

@@ -68,8 +68,7 @@ end
 -- This layout only accept one children, all others will be ignored
 -- @tparam table children A table composed of valid widgets
 function mirror:set_children(children)
-    self.widget = children and children[1]
-    self:emit_signal("widget::layout_changed")
+    self:set_widget(children[1])
 end
 
 --- Reset this layout. The widget will be removed and the axes reset.

lib/wibox/layout/rotate.lua

@@ -76,8 +76,7 @@ end
 -- This layout only accept one children, all others will be ignored
 -- @tparam table children A table composed of valid widgets
 function rotate:set_children(children)
-    self.widget = children and children[1]
-    self:emit_signal("widget::layout_changed")
+    self:set_widget(children[1])
 end
 
 --- Reset this layout. The widget will be removed and the rotation reset.

lib/wibox/layout/scroll.lua

@@ -267,8 +267,7 @@ end
 -- This layout only accept one children, all others will be ignored
 -- @tparam table children A table composed of valid widgets
 function scroll:set_children(children)
-    self.widget = children and children[1]
-    self:emit_signal("widget::layout_changed")
+    self:set_widget(children[1])
 end
 
 --- Specify the expand mode that is used for extra space.

lib/wibox/widget/background.lua

@@ -109,8 +109,7 @@ end
 -- This layout only accept one children, all others will be ignored
 -- @tparam table children A table composed of valid widgets
 function background:set_children(children)
-    self.widget = children and children[1]
-    self:emit_signal("widget::layout_changed")
+    self:set_widget(children[1])
 end
 
 --- Set the background to use