Skipping asset precompile

Waiting on asset precompilation is a PITA, especially if no assets have been changed. Thankfully, Ben Curtis came up with a workable solution. Except...

Ben's method fails on the initial deployment, because current_revision tries to read /path/to/app/current/REVISION, which won't exist yet. After trying several approaches, I have arrived at one which works for me. There are probably other, more elegant approaches, but this one seems clear enough for my purposes. Posting it here for posterity.

namespace :deploy do
  namespace :assets do
    task :precompile, roles: :web, except: {no_release: true} do
      from = source.next_revision(current_revision) if capture("[ -f #{File.join(current_path, 'REVISION')} ] || echo '1'").empty?
      if from.nil? || capture("cd #{latest_release} && #{source.local.log(from)} vendor/assets app/assets lib/assets | wc -l").to_i > 0
        run %Q{cd #{latest_release} && #{rake} RAILS_ENV=#{rails_env} #{asset_env} assets:precompile}
      else
        logger.info "Skipping asset pre-compilation because there were no asset changes."
      end
    end
  end
end