ActionView::Template::Error: stack level too deep

[abrisse]

When migrating from rabl to rabl-rails I encounter a problem. Let's say you have 2 views in which you can extends each other under 2 different conditions that cannot be true at the same time.

Postulate : condition_A = !condition_B

# x/show.rabl
object :@x
attributes :id

condition(->(_) { condition_A } do
  extends 'y/show'
end

# y/show.rabl
object :@y
attributes :id

condition(->(_) { condition_B } do
  extends 'x/show'
end

That case triggers a ActionView::Template::Error: stack level too deep error when rendered. I guess that because the views are compiled contrary to the rabl gems.

[ccocchi]

Hmm no, this should word because extends will only be called if the condition is true. I think the problem is that both your condition are true in your case.

[abrisse]

@ccocchi : this is definitely a bug. Try to define in a rabl template 'items/show.rabl' :

object @resource

condition(->(item) { false }) do
  extends 'items/show'
end

It will raise :

ActionView::Template::Error (stack level too deep):
  rabl-rails (0.3.1) lib/rabl-rails/compiler.rb:17

Looks like the block is executed even if the condition is false. In fact the block won't be displayed if the condition is false but will nevertheless be executed.

[ccocchi]

You're right, condition body are evaluated at compilation time so it will raise, but it is not a bug. You're trying to introduce a circular reference which is never a good idea, and is often due to a bad design so it won't be added to rabl-rails.

You can resolve your issue by extracting into a partial everything you will need in your x template from y template, and include it once in your y template and once in your x template inside your condition body. This way you will never a case of circular reference, which is a lot safer in my opinion.

[brunoald]

I can't see a problem on using circular references when you have a clear "breakpoint". As far as I know, most recursive algorithms work based on this premise. You should only be careful ensuring there's always a "breakpoint". In my opinion, recursive structures are not necessarily bad design. It might be the case that they're a requirement. I'm trying to create a recursive JSON structure of comments within comments, but I'm getting the same problem that abrisse got.

[ccocchi]

You're right, it makes sense when you're doing recursive templates, but that's different from what @abrisse was trying to achieve.

At the moment you won't be able to use extends with recursivity because of how rabl-rails works. Since templates are "compiled" into plain ruby objects without any context, the break condition will never be evaluated, hence the stack error.

But we could imagine a new directive extends_recursive "some_template", ->(obj) { break condition }) that would delegate extends replacement at rendering time unless the break condition is met.