render_to_string not working when upgrading to Rails 6.1

[oboxodo]

Hi there 👋 ,

I'm upgrading a big app from Rails 6.0 to 6.1. We use ViewComponent v2.34.0.

After upgrading one of our tests fails because some code like my_html = render_to_string(MyViewComponent.new) is returning an empty string ("") instead of the rendered component.

I understand Rails 6.1 should support ViewComponent nativelly and it does when using render, but apparently not when using render_to_string. After looking at the monkey patch for version < 6.1 I was able to make it work with my_html = MyViewComponent.new.render_in(view_context).

But shouldn't render_to_string still work? Or at least be mentioned in the docs? Did I miss something? Is this the best place to get what I want?

Thanks!

[joelhawksley]

@oboxodo thanks for the report!

We do have an integration test for render_to_string (https://github.com/github/view_component/blob/main/test/view_component/integration_test.rb#L77) that runs in CI against Rails 5, 6, 6.1, and main, but I wonder if your case is not covered by our test suite.

Might you be up for trying to introduce a PR with a failing test for this bug?

[oboxodo]

Thanks for the pointer, @joelhawksley!

I found how to reproduce the problem. Comparing execution of my code vs that automated test of yours, I noticed execution goes the same until it hits this line. In there, my code does have a layout but your test doesn't.

With that in mind, I'm able to fix my code by changing from:

my_html = render_to_string(MyViewComponent.new)

to:

my_html = render_to_string(MyViewComponent.new, layout: false)

instead of the uglier workaround:

my_html = MyViewComponent.new.render_in(view_context)

I was able to make the ViewComponent render_to_string test fail by changing this line from layout false to layout "application".

I hope this new information is helpful for you guys to dig a bit deeper. Including a layout shouldn't make the component disappear.

I'm sadly not able to dedicate much more time to this now and I actually think our code is better with the explicit layout: false considering I just want the component's HTML.

But it's still a change of behavior in ViewComponent with vs without the monkey patches in Rails 6.1 so you might want to at least document it.

[joelhawksley]

I've verified that this isn't an issue in #2339.