Version 2.19.0 causes an infinite loop with the LTS version of activesupport 4.2.11.40

[rwadstein]

I realize we are still on an older version of Rails 4 and we are actively converting it to go to a newer version.
In the meantime, just want to point out going from 2.18.1 to 2.19.0 caused an infinite loop when using the #to_json method.

Currently, we are just using != '2.19.0' in the Gemfile in hopes that this will be addressed, but realize that such an older version may not constitute a fix. Just for reference there is no problem when using it with Rails 5 LTS.

[byroot]

It's likely a consequence of #941

I can't promise I can fix it, but I'd appreciate if you could provide a reproduction script so I can investigate the feasibility of fixing it.

[byroot]

I tried to repro with the little information available, but no luck:

require "bundler/inline"

gemfile do
  gem "activesupport", "4.2.11.3"
  gem "json", "2.19.0"
end

class Some
  def as_json(...)
    {obj: 1}
  end
end

puts([{foo: 1, bar: Some.new}].to_json)

So until I get a repro script or at least some more details, my hands are tied.

[rwadstein]

No problem. Thanks for the help. I figured this might be an issue for Rails LTS versions rather than for json since yours works with the last official release. Since Rails LTS are the ones that have extended the last supported version of Rails 4.2, I'll try to reach out to them.
thanks again.

[rwadstein]

I was double checking a few things, and found a script that will easily create the problem, but requires going back to ruby 2.7
Rails LTS supports allows ruby 3+ with the newer versions of BigDecimal, but going back to ruby 2.7 and I can still create the same problem.

require "bundler/inline"

gemfile do
  gem "activesupport", "4.2.11.3"
  gem "json", "2.19.0"
  gem "bigdecimal", "1.4.4"
end

require 'active_support/all'

puts([{foo: 1, bar: "asdf"}].to_json)

Traceback (most recent call last):
       16: from /usr/local/bundle/gems/activesupport-4.2.11.3/lib/active_support/core_ext/object/json.rb:34:in 
...
        1: from /usr/local/bundle/gems/activesupport-4.2.11.3/lib/active_support/core_ext/object/json.rb:34:in `to_json_with_active_support_encoder'
SystemStackError (stack level too deep)

[rwadstein]

We are actively trying to go to Rails 5, so we can easily just lock it to < 2.19 for now.
I guess at this point, this is just for context if you decide you want to fix it or not.

[byroot]

Ok I see. I'm afraid I can't fix that, except by reverting what I believe to be an important improvement.

Rails 4.x is tightly coupled to to_json methods being defined on specific classes.

You can monkey patch to fix the problem though:

require "bundler/inline"

gemfile do
  source 'https://rubygems.org'
  gem "stringio"
  gem "activesupport", "4.2.11.3"
  gem "json", "2.19.0"
  gem "bigdecimal", "1.4.4"
  gem "logger"
  gem "base64"
  gem "mutex_m"
  gem "benchmark"
end

require 'active_support/all'

# Remove custom methods from everywhere but `Object`.
[Enumerable, Array, FalseClass, Float, Hash, Integer, NilClass, String, TrueClass].each do |klass|
  klass.class_eval do
    remove_method :to_json
    remove_method :to_json_without_active_support_encoder
  end
end

puts([{foo: 1, bar: "asdf"}].to_json)

Sorry, I can't do any better than that.