Now using ant task

[ylemoigne]

If someone looking here, sample using the xtend ant task (available since xtend 2.4.2)

configurations {
    xtendc
}

dependencies {
    compile 'org.eclipse.xtend:org.eclipse.xtend.lib:2.4.2'
    compile 'org.eclipse.xtext:org.eclipse.xtext.xbase.lib:2.4.2'

    xtendc 'org.eclipse.xtend:org.eclipse.xtend.standalone:2.4.2'
}

task compileXtend << {
    ant.taskdef(name: 'xtendc', classname: 'org.eclipse.xtend.core.compiler.batch.XtendCompilerAntTask', classpath: configurations.xtendc.asPath)
    ant.xtendc(destdir: 'src/main/generated-sources') {
        srcdir {
            sourceSets.main.java.srcDirs.findAll { it.exists() }.each {
                pathelement(path: it)
            }
        }
        classpath {
            pathelement(path: configurations.xtendc.asPath)
            sourceSets.main.compileClasspath.each {
                pathelement(location: it)
            }
        }
    }
}

tasks.compileJava.dependsOn compileXtend