359: Add block back into render call

[dorner]

No description provided.

[delner]

Interesting, and also a bit surprising this wasn't being passed. Do you have an example of something passing a block to render?

[delner]

Looks like we also aren't passing blocks for other render functions.

Could you add the same to https://github.com/wishabi/dd-trace-rb/blob/b3f848044035fd330fc43fcee80200c633c596c4/lib/ddtrace/contrib/rails/core_extensions.rb#L98?

[dorner]

@delner render_partial doesn't take a block like render does. The block is handled separately. Same for _render_template.

For an example, here's the way it looks in our code:

<%=
  render :layout => 'ad_set_group_tabs',
    :locals => {
    :ad_sets_in_groups => @ad_sets_in_groups,
    :remote => true,
    :show_workflow => true
  } do |ad_sets, id|
    show_ad_set_group_gma_campaign_path(:group_id => id || -1)
  end
%>

This is definitely a rather obscure way of using render and I'm not surprised it hasn't been brought up before. :) Here's another example: https://stackoverflow.com/questions/2951105/rails-render-partial-with-block

[delner]

Cool, the context there is helpful.

But I think the point of adding block to the partial renderer still applies, since the PartialRenderer does actually take a block for render and the tracer isn't fowarding the block. Or am I misunderstanding?

[dorner]

@delner yep. :) If you follow the code, here's what's happening:

• PartialRender calls render
• This takes a block, i.e. a Proc as an argument (not an actual Ruby block)
• The block is saved in an instance variable
• render then calls render_partial without any arguments
• render_partial uses the instance variable saved previously to render

The patcher patches the render_partial method, not the render method, so all of the block handling should be managed entirely without the patched method caring about it.

Just took a closer look - so the patcher does patch the render method, but since the block being passed is an actual variable and not a Ruby block, it should be covered by *args.

[delner]

Oh, whoops, you're right: block is being passed as a normal parameter in the PartialRenderer. My eye was just automatically adding the & to it. Looks like the &block in def render_with_datadog(*args, &block) patch for PartialRenderer doesn't actually match the parameter list for the function its displacing.

We should probably remove that extraneous &block from that function def, but otherwise it looks like it shouldn't suffer the same issue. Thanks for correcting me!