Add various functions for getting directories

This adds functions for getting directories according to the XDG base dir
specification. This might be useful in general.

This also adds a function for getting the cache dir, because I like an explicit
function call more than something which "switches" based on a string argument.
Better error messages if you mis-type something. :-)

Finally, this adds a function for getting the directory containing the rc.lua
file. Sadly, awful.util.getdir("config") did not actually do that. See #218.

Fixes: https://github.com/awesomeWM/awesome/issues/218
Signed-off-by: Uli Schlachter <psychon@znc.in>

lib/awful/util.lua

@@ -133,6 +133,31 @@ function util.restart()
     capi.awesome.restart()
 end
 
+--- Get the config home according to the XDG basedir specification.
+-- @return the config home (XDG_CONFIG_HOME) with a slash at the end.
+function util.get_xdg_config_home()
+    return (os.getenv("XDG_CONFIG_HOME") or os.getenv("HOME") .. "/.config") .. "/"
+end
+
+--- Get the cache home according to the XDG basedir specification.
+-- @return the cache home (XDG_CACHE_HOME) with a slash at the end.
+function util.get_xdg_cache_home()
+    return (os.getenv("XDG_CACHE_HOME") or os.getenv("HOME") .. "/.cache") .. "/"
+end
+
+--- Get the path to the user's config dir.
+-- This is the directory containing the configuration file ("rc.lua").
+-- @return A string with the requested path with a slash at the end.
+function util.get_configuration_dir()
+    return capi.awesome.conffile:match(".*/") or "./"
+end
+
+--- Get the path to a directory that should be used for caching data.
+-- @return A string with the requested path with a slash at the end.
+function util.get_cache_dir()
+    return util.get_xdg_cache_home() .. "awesome/"
+end
+
 --- Get the user's config or cache dir.
 -- It first checks XDG_CONFIG_HOME / XDG_CACHE_HOME, but then goes with the
 -- default paths.
@@ -140,17 +165,11 @@ end
 -- @return A string containing the requested path.
 function util.getdir(d)
     if d == "config" then
-        local dir = os.getenv("XDG_CONFIG_HOME")
+        -- No idea why this is what is returned, I recommend everyone to use
-        if dir then
+        -- get_configuration_dir() instead
-            return dir .. "/awesome"
+        return util.get_xdg_config_home() .. "awesome/"
-        end
-        return os.getenv("HOME") .. "/.config/awesome"
     elseif d == "cache" then
-        local dir = os.getenv("XDG_CACHE_HOME")
+        return util.get_cache_dir()
-        if dir then
-            return dir .. "/awesome"
-        end
-        return os.getenv("HOME").."/.cache/awesome"
     end
 end