All memory consumed when running tests

[seanlinsley]

I'm currently working on activeadmin/activeadmin#3298 to get Active Admin's test suite passing again using the latest version of RSpec. As noted on that ticket, I can't locally reproduce the error that Travis is failing on; instead I discovered that a823c9f in particular causes all available memory to be consumed.

This issue seems to only occur for a single test, which happens to use include.

rspec spec/unit/views/components/paginated_collection_spec.rb:47

I can reproduce this on both Ruby 2.1.1 and 2.1.2. I made sure to bundle update during all this, but let me know if you'd still like a Gemfile.lock

[myronmarston]

Thanks for providing clear repro instructions!

The memory consumption happens because in that spec, pagination is defined in such a way that [pagination].flatten will recurse infinitely (but will do so in a way that doesn't exhaust the stack!), causing the memory consumption spike. You can see this happen if you remove the expect lines and put [pagination].flatten instead -- you'll get the same thing. There's a spot internally in RSpec where it flattens an array that happens to have your object in it, and it hits this.

I believe the source of the problem is the fact that Arbre::Element#to_ary is defined in such a way that it includes self in the returned collection:

https://github.com/gregbell/arbre/blob/fe4738844d7d4b9db0b1b46af889310854cd316e/lib/arbre/element.rb#L149-L151

flatten recursively calls to_ary on the receiver, then on the individual elements returned by that, then on the individual elements returned by that, etc, so as long as you are including self in the return value of to_ary, it will recurse forever.

As it turns out, rack and rails have both had this bug in the past:

• [response].flatten causes infinite loop rack/rack#419
• Prevent [response].flatten from recursing infinitely. rails/rails#13921
• Fix response flatten infinite recursion rails/rails#13982

...so you may be able to use a similar solution to how they solved it.

[seanlinsley]

I can reproduce as well with Arbre::Element.new.to_a.flatten. Thanks for looking into this 🐱