Merge pull request #2800 from psychon/fix_negative_sizes

Fix negative sizes with the margin container

lib/wibox/container/margin.lua

@@ -44,7 +44,12 @@ function margin:layout(_, width, height)
         local w = self._private.right
         local h = self._private.bottom
 
-        return { base.place_widget_at(self._private.widget, x, y, width - x - w, height - y - h) }
+        local resulting_width = width - x - w
+        local resulting_height = height - y - h
+
+        if resulting_width > 0 and resulting_height > 0 then
+            return { base.place_widget_at(self._private.widget, x, y, resulting_width, resulting_height) }
+        end
     end
 end
 

lib/wibox/hierarchy.lua

@@ -304,8 +304,8 @@ end
 
 --- Does the given cairo context have an empty clip (aka "no drawing possible")?
 local function empty_clip(cr)
-    local _, _, width, height = cr:clip_extents()
-    return width == 0 or height == 0
+    local x1, y1, x2, y2 = cr:clip_extents()
+    return x2 - x1 == 0 or y2 - y1 == 0
 end
 
 --- Draw a hierarchy to some cairo context.

lib/wibox/widget/base.lua

@@ -397,6 +397,8 @@ end
 -- @treturn table An opaque object that can be returned from `:layout()`.
 -- @staticfct wibox.widget.base.place_widget_via_matrix
 function base.place_widget_via_matrix(widget, mat, width, height)
+    assert(width >= 0, "A widget's width cannot be negative: " ..  tostring(width))
+    assert(height >= 0, "A widget's height cannot be negative: " ..  tostring(height))
     return {
         _widget = widget,
         _width = width,