groovy's AntBuilder and external ant tasks (example with Google Closure The JavaScript Compiler)

gistfile1.groovy

import groovy.grape.Grape;

// to explain why I am not using @Grape annotation
// see http://stackoverflow.com/questions/1641116/groovy-with-grape-and-antbuilder-classloader-problem
Grape.grab(
            group: 'com.google.javascript',
            module: 'closure-compiler',
            version: 'r1918',
            classLoader:this.class.classLoader.rootLoader /* needed because of ant.taskdef classloader */)

def ant = new AntBuilder()

// https://developers.google.com/closure/compiler/
ant.taskdef(name: 'compileJs', classname: 'com.google.javascript.jscomp.ant.CompileTask')

ant.compileJs(
         compilationLevel: "whitespace", /* next values are 'simple' and 'advance' - see http://bit.ly/JfZROa */ 
         warning: "verbose", 
         debug: "true", 
         output: /... insert path to result file here .../) {
                    
         sources(
             dir: "... insert root dir where to find files in files property",
             files: "first.js, second.js, insert_your_name.js")
                
}