feat(config): better error when Coffee/Live Script not installed

lib/config.js

@@ -5,16 +5,21 @@ var log = logger.create('config');
 var helper = require('./helper');
 var constant = require('./constants');
 
+var COFFEE_SCRIPT_AVAILABLE = false;
+var LIVE_SCRIPT_AVAILABLE = false;
+
 // Coffee is required here to enable config files written in coffee-script.
 // It's not directly used in this file.
 try {
   require('coffee-script').register();
+  COFFEE_SCRIPT_AVAILABLE = true;
 } catch (e) {}
 
 // LiveScript is required here to enable config files written in LiveScript.
 // It's not directly used in this file.
 try {
   require('LiveScript');
+  LIVE_SCRIPT_AVAILABLE = true;
 } catch (e) {}
 
 var Pattern = function(pattern, served, included, watched) {
@@ -244,6 +249,15 @@ var parseConfig = function(configFilePath, cliOptions) {
         log.error('File %s does not exist!', configFilePath);
       } else {
         log.error('Invalid config file!\n  ' + e.stack);
+
+        var extension = path.extname(configFilePath);
+        if (extension === '.coffee' && !COFFEE_SCRIPT_AVAILABLE) {
+          log.error('You need to install CoffeeScript.\n' +
+                    '  npm install coffee-script --save-dev');
+        } else if (extension === '.ls' && !LIVE_SCRIPT_AVAILABLE) {
+          log.error('You need to install LiveScript.\n' +
+                    '  npm install LiveScript --save-dev');
+        }
       }
       return process.exit(1);
     }