When I updated from Rails 7.0 to 7.1 javascript_pack_tag started double rendered

[ipepe]

Expected behavior:

On Rails 7.1 with haml templating engine javascript_pack_tag doesn't double render.

Actual behavior:

On Rails 7.1 with haml templating engine javascript_pack_tag does double render its content because of capture method here: https://github.com/shakacode/shakapacker/blob/main/lib/shakapacker/helper.rb#L117 returning a string content, when the method javascript_pack_tag should return nil like this:

  def javascript_pack_tag(*names, defer: true, async: false, **options)
    if @javascript_pack_tag_loaded
      raise "To prevent duplicated chunks on the page, you should call javascript_pack_tag only once on the page. " \
      "Please refer to https://github.com/shakacode/shakapacker/blob/main/README.md#view-helpers-javascript_pack_tag-and-stylesheet_pack_tag for the usage guide"
    end

    append_javascript_pack_tag(*names, defer: defer, async: async)
    sync = sources_from_manifest_entrypoints(javascript_pack_tag_queue[:sync], type: :javascript)
    async = sources_from_manifest_entrypoints(javascript_pack_tag_queue[:async], type: :javascript) - sync
    deferred = sources_from_manifest_entrypoints(javascript_pack_tag_queue[:deferred], type: :javascript) - sync - async

    @javascript_pack_tag_loaded = true

    capture do
      render_tags(async, :javascript, **options.dup.tap { |o| o[:async] = true })
      concat "\n" if async.any? && deferred.any?
      render_tags(deferred, :javascript, **options.dup.tap { |o| o[:defer] = true })
      concat "\n" if sync.any? && deferred.any?
      render_tags(sync, :javascript, options)
    end

    nil # prevent double render (this is missing in Shakapacker's original code)
  end

Small, reproducible repo:

I don't have it yet, will work on reproducing this issue

Setup environment:

• Ruby version: 3.2.8
• Rails version: 7.1.5.2
• Shakapacker version: 8.3.0
• HAML: 5.1.2
• HAML-RAILS: 2.1.0

[ipepe]

I have also noticed that chaging:

= javascript_pack_tag 'application'

to

- javascript_pack_tag 'application'

Fixes the problem. Although I'm not sure this is a correct solution. Problem also doesn't occur in ERB templates.

[justin808]

@ipepe maybe the second one just runs the code but doesn't put the result on the template?

[G-Rath]

I'm pretty sure the answer is you should be using - - all that capture does is build a string which then gets returned, with some buffer and sanitizing sugar:

      def capture(*args, &block)
        value = nil
        @output_buffer ||= ActionView::OutputBuffer.new
        buffer = @output_buffer.capture { value = yield(*args) }

        string = if @output_buffer.equal?(value)
          buffer
        else
          buffer.presence || value
        end

        case string
        when OutputBuffer
          string.to_s
        when ActiveSupport::SafeBuffer
          string
        when String
          ERB::Util.html_escape(string)
        end
      end

so the helper is correct in returning the result of the capture.

I suspect what is happening is the HAML gem is doing something related to capture, which is supported by some of its code and changelog entries.