gears.object.properties: Use the new .data table

Previously, gears.object.properties used a weak table for adding
additional information to a C object. However, weak tables can easily
cause leaks when the value references the key.

This commit makes the code instead use the new .data property that is
available on all C objects. This means we have no more magic with a weak
table and instead only use "regular" tables instead.

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

lib/gears/object/properties.lua

@@ -10,22 +10,6 @@
 
 local object = {}
 
-local properties = setmetatable({}, { __mode = 'k' })
-
-local function cobj_register(cobj)
-    local fallback = {}
-
-    function fallback:rawset(_, prop, val)
-        fallback[prop] = val
-    end
-
-    function fallback:rawget(_, prop)
-        return fallback[prop]
-    end
-
-    properties[cobj] = fallback
-    return fallback
-end
 
 --- Add the missing properties handler to a CAPI object such as client/tag/screen.
 -- Valid args:
@@ -66,10 +50,8 @@ function object.capi_index_fallback(class, args)
             return args.getter_fallback(cobj, prop)
         end
 
-        local fallback = properties[cobj] or cobj_register(cobj)
-
         -- Use the fallback property table
-        return fallback[prop]
+        return cobj.data[prop]
     end
 
     local setter = args.setter or function(cobj, prop, value)
@@ -88,10 +70,8 @@ function object.capi_index_fallback(class, args)
             return
         end
 
-        local fallback = properties[cobj] or cobj_register(cobj)
-
         -- Use the fallback property table
-        fallback[prop] = value
+        cobj.data[prop] = value
 
         -- Emit the signal
         if args.auto_emit then