diff-assets.rake

    desc "Compare frontend asset builds between branches"
    task :diffassets, [:branch] do |t, args|
      sh "git diff-index --quiet HEAD --" do |ok, res|
        abort "Working directory not clean. Stash or commit first." unless ok
      end

      args.with_defaults(branch: "-") # git's magic for "last branch"

      # start in main, do clean asset build, and temporarily force-add to git
      sh "git switch main"
      sh "rake assets:clobber assets:precompile"
      sh "git add -f app/assets public"

      # switch (back) to feature branch, rebuild, and diff
      sh "git switch #{args[:branch]}"
      sh "rake assets:clobber assets:precompile"
      sh "git diff --stat"
    end