awful: Set a miss handler for capi.root

There is no better place to put it and need to always be required
for backward compatibility. Given Awesome no longer works properly
without `awful`, I put the code there.

.luacheckrc

@@ -26,7 +26,6 @@ read_globals = {
     "key",
     "keygrabber",
     "mousegrabber",
-    "root",
     "selection",
     "tag",
     "window",
@@ -43,6 +42,7 @@ read_globals = {
 globals = {
     "screen",
     "mouse",
+    "root",
     "client"
 }
 

lib/awful/_compat.lua

@@ -5,6 +5,8 @@ local util   = require("awful.util" )
 local spawn  = require("awful.spawn")
 local gdebug = require("gears.debug")
 
+local capi = {root = root}
+
 function timer(...) -- luacheck: ignore
     gdebug.deprecate("gears.timer", {deprecated_in=4})
     return gtimer(...)
@@ -25,3 +27,32 @@ util.pread = function()
             .. "for an asynchronous alternative", {deprecated_in=4})
     return ""
 end
+
+-- Allow properties to be set on the root object. This helps to migrate some
+-- capi function to an higher level Lua implementation.
+do
+    local root_props, root_object = {}, {}
+
+    capi.root.set_newindex_miss_handler(function(_,key,value)
+        if root_object["set_"..key] then
+            root_object["set_"..key](value)
+        elseif not root_object["get_"..key] then
+            root_props[key] = value
+        else
+            -- If there is a getter, but no setter, then the property is read-only
+            error("Cannot set '" .. tostring(key) .. " because it is read-only")
+        end
+    end)
+
+    capi.root.set_index_miss_handler(function(_,key)
+        if root_object["get_"..key] then
+            return root_object["get_"..key]()
+        else
+            return root_props[key]
+        end
+    end)
+
+    root._private = {}
+    root.object = root_object
+    assert(root.object == root_object)
+end

tests/examples/shims/root.lua

@@ -176,13 +176,29 @@ end
 
 
 function root.set_newindex_miss_handler(h)
-    rawset(mouse, "_ni_handler", h)
+    rawset(root, "_ni_handler", h)
 end
 
 function root.set_index_miss_handler(h)
-    rawset(mouse, "_i_handler", h)
+    rawset(root, "_i_handler", h)
 end
 
-return root
+return setmetatable(root, {
+    __index = function(self, key)
+        if key == "screen" then
+            return screen[1]
+        end
+        local h = rawget(root,"_i_handler")
+        if h then
+            return h(self, key)
+        end
+    end,
+    __newindex = function(...)
+        local h = rawget(root,"_ni_handler")
+        if h then
+            h(...)
+        end
+    end,
+})
 
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