Unexpected behaviour when yielding a block of ERB

[joeldrapper]

I have a method that captures a block of ERB, e.g.

<%= my_method do %>
  <h1>Hello</h1>
<% end %>

In ActionView, yielding this block causes the heading to be appended to the view_context.output_buffer but in ViewComponent, it returns \n and adds nothing to the output buffer.

Is ViewComponent using a different buffer? This is essentially what my method is doing:

def my_method
  view_context.with_output_buffer(my_buffer) do
    my_output = yield
  end
  my_buffer
end

But the heading is never added to my_output or my_buffer.

I’ve tried to simplify this as much as possible. The real failing code can be found here. https://github.com/joeldrapper/phlex-rails/blob/3fb1d6be45be886470f54f0883347506c6b7c683/lib/phlex/rails/renderable.rb#L19-L35 and reproduction of the issue is available here. phlex-ruby/phlex#368 (comment)