babushka-conf.rb

dep 'erb config', :src, :dest do
  met? {
    Babushka::Renderable.new(dest).from?(dependency.load_path.parent / src)
  }
  meet {
    render_erb src, :to => dest
  }
end

dep 'app' do
  requires [
    'app.bin',
    'erb config'.with('app/app.conf.erb', '/etc/app.conf')
  ]
end

I suspect this will not work if the template erb is not relative to the source file of the source containing this dep, because it uses dependency.load_path.