Commit bd47edb4e is (possibly) wrong

[psychon]

Commit bd47edb changed the widget_dependencies table in wibox.widget.base to have __mode = "kv". However, the v in there is wrong: This table will always have the only reference to its values. Its a list of widgets specific to this entry!
The effect of this should be that the fit and layout caches are not properly invalidated if an "inner" widget changes after a garbage collection cycle...

However, these are fit and layout caches. This means that they also get cleared by the garbage collector. Since all uses of these caches first call record_dependency, which in turn touches the existing widget_dependencies[child] table, I think the garbage collector cannot collect the dependencies table without also collecting the caches that are protected by this.

Another however: I am not really sure about the above and depending on special/magical GC behaviour like this just asks for trouble. Something like the following should be given some thought:

diff --git a/lib/wibox/widget/base.lua b/lib/wibox/widget/base.lua
index 80853c72..ae48bcfe 100644
--- a/lib/wibox/widget/base.lua
+++ b/lib/wibox/widget/base.lua
@@ -210,7 +210,7 @@ end
 -- {{{ Caches
 
 -- Indexes are widgets, allow them to be garbage-collected.
-local widget_dependencies = setmetatable({}, { __mode = "kv" })
+local widget_dependencies = setmetatable({}, { __mode = "k" })
 
 -- Get the cache of the given kind for this widget. This returns a gears.cache
 -- that calls the callback of kind `kind` on the widget.
@@ -239,7 +239,7 @@ local function record_dependency(parent, child)
     base.check_widget(parent)
     base.check_widget(child)
 
-    local deps = widget_dependencies[child] or {}
+    local deps = widget_dependencies[child] or setmetatable({}, {__mode="v"})
     deps[parent] = true
     widget_dependencies[child] = deps
 end
@@ -248,7 +248,7 @@ end
 local clear_caches
 function clear_caches(widget)
     local deps = widget_dependencies[widget] or {}
-    widget_dependencies[widget] = {}
+    widget_dependencies[widget] = setmetatable({}, {__mode="v"})
     widget._private.widget_caches = {}
     for w in pairs(deps) do
         clear_caches(w)

(To do: Instead of recreating the metatable all the time, it should only be created once; also, if record_dependency unconditionally set the metatable, then clear_caches could just be left alone.)