awful: add helper to check configuration file syntax

Signed-off-by: Julien Danjou <julien@danjou.info>

awesomerc.lua.in

@@ -217,7 +217,10 @@ keybinding({ modkey }, "Escape", awful.tag.history.restore):add()
 -- Standard program
 keybinding({ modkey }, "Return", function () awful.util.spawn(terminal) end):add()
 
-keybinding({ modkey, "Control" }, "r", awesome.restart):add()
+keybinding({ modkey, "Control" }, "r", function ()
+                                           mypromptbox.text =
+                                               awful.util.escape(awful.util.restart())
+                                        end):add()
 keybinding({ modkey, "Shift" }, "q", awesome.quit):add()
 
 -- Client manipulation

lib/awful/util.lua.in

@@ -11,6 +11,7 @@ local assert = assert
 local loadstring = loadstring
 local debug = debug
 local print = print
+local type = type
 local capi =
 {
     awesome = awesome,
@@ -109,4 +110,41 @@ function unescape(text)
     return text
 end
 
+--- Check if a file is a Lua valid file.
+-- This is done by loading the content and compiling it with loadstring().
+-- @param path The file path.
+-- @return A function if everything is alright, a string with the error
+-- otherwise.
+function checkfile(path)
+    if not path then return "E: no file given" end
+    local f = io.open(path)
+
+    if not f then
+        return "E: unable to open file " .. path
+    end
+
+    local s = f:read("*all")
+
+    f:close()
+
+    local f, e = loadstring(s)
+    -- Return function if function, otherwise return error.
+    if f then return f end
+    return e
+end
+
+--- Try to restart awesome.
+-- It checks if the configuration file is valid, and then restart if it's ok.
+-- If it's not ok, the error will be returned.
+-- @return Never return if awesome restart, or return a string error.
+function restart()
+    local c = checkfile(capi.awesome.conffile())
+
+    if type(c) ~= "function" then
+        return c
+    end
+
+    capi.awesome.restart()
+end
+
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