[v4] Troubleshooting issue with Slim

[edolix]

What are you trying to accomplish?

Trying to upgrade ViewComponent to v4 in one of our apps, @xkraty and i noticed a lot of failures in CI like: Couldn't find a template file or inline render method for SomeSlimComponent.... I was like 🤔
We use Slim everywhere and everything worked as expected with v3.

I tried to dig a bit and i think it could be a race condition between Slim initialization and the cache logic for each component.
I may be wrong so apologies in case all of this doesn't make sense!

In order:

In ViewComponent::Base inherited each component will be automatically compiled (and then cached) as soon as the file is loaded:

view_component/lib/view_component/base.rb

Lines 544 to 547 in 6a33362

	def inherited(child)
	# Compile so child will inherit compiled `call_*` template methods that
	# `compile` defines
	__vc_compile

The problem comes with the Slim gem that will register the slim template handler only at the action_view hook causing a (possible) race condition within the ViewComponent::Compiler.gather_templates method:

view_component/lib/view_component/compiler.rb

Lines 177 to 179 in 6a33362

	templates = @component.sidecar_files(
	ActionView::Template.template_handler_extensions
	).map do |path|

ActionView::Template.template_handler_extensions might not include "slim" at that point.

All templates are gonna be memoized (with the related template_errors as well).

If few components got loaded (and automatically cached due to ViewComponent::Base.inherited) before the action_view hook (that will register slim as a valid template handler)... those components will always raise the Couldn't find a template file or inline render method for ....

What approach did you choose and why?

We created a Rails app trying to reproduce the issue with no luck. I'll try again tomorrow on it.

This PR is a basic/raw/dumb attempt to - at least - highlight the issue and give more context.

Anything you want to highlight for special attention from reviewers?

Nothing - just thanks for the great VC gem! 🙌

[edolix]

note: today i found other two apps where v4 + Slim caused the CI to fail with the same errors

[joelhawksley]

@edolix thank you for the report and for following up about seeing this issue elsewhere. I too was unable to reproduce it in https://github.com/ViewComponent/demo. (I've now added Slim to the test suite so you can try to reproduce it there if you'd like)

Please keep us posted as you work to reproduce it in isolation- we don't use Slim at GitHub so I can't dedicate much time to this issue at the moment ❤️

[edolix]

@joelhawksley i found a way to reproduce it in this repo: https://github.com/edolix/view-component-bug-replica

I added piece by piece until i got the same behavior of my apps - i'm adding more info in the README but let me know if you see the same errors 🙏
Thank you!