Conditionally copy foo

Brocfile.js

var Funnel = require('broccoli-funnel')
var MergeTrees = require('broccoli-merge-trees')

var trees = []

var currentIndex = new Funnel('.', {
  include: ['index.html'],
  destDir: 'current'
})
trees.push(currentIndex)

if (process.env.FOO) {
  var fooIndex = new Funnel('.', {
    include: ['index.html'],
    destDir: 'foo'
  })
  trees.push(fooIndex)
}

module.exports = new MergeTrees(trees)

$ broccoli build dist
$ find dist
dist
dist/current
dist/current/index.html

$ FOO=1 broccoli build dist
$ find dist
dist
dist/current
dist/current/index.html
dist/foo
dist/foo/index.html