Error: Unable to Find Matching Line from Backtrace


January 15, 2014

You’ve just upgraded to Ruby 2.1 and Ruby is hitting you back with this error?

Failure/Error: Unable to find matching line from backtrace
ArgumentError:
comparison of NilClass with 0 failed

You are not alone.

Looks like the GC module has been updated in Ruby MRI 2.1 and returning different hash keys now. In my case, this is what caused this error in RSpec spec/spec_helper.rb:

1
2
3
config.after(:each) do
  slots_number = [slots_number, GC.stat[:heap_live_num]].max
end

Since, there is no longer :heap_live_num hash key returned by Ruby 2.1 GC.stat method, .max method throws an argument error while trying to compare against nil.

The fix was to replace the outdated :heap_live_num key with the new :heap_live_slot one:

1
2
3
config.after(:each) do
  slots_number = [slots_number, GC.stat[:heap_live_slot]].max
end

And we are back in green land now.

So, check to see whether you are referencing the latest hash keys of the GC.stat hash.


##### Today my environment was:

  • Rails 4.0.2
  • MRI Ruby 2.1.0
  • Rspec-rails 2.14.1