The key is the "unless const_defined?(...)".
It says that the constant should be defined and frozen, UNLESS it is aready
defined.
How do you define it before ActionView::Helpers::InstanceTag is defined?.
Well, just define it at the beginning of environment.rb, however, since
neither ActionView, Helpers or InstanceTag is defined yet, we must define
them fully with Module/Class...End blocks like this:
module ActionView
module Helpers
class InstanceTag
DEFAULT_TEXT_AREA_OPTIONS = { :cols => 60, :rows => 10 }
end
end
end
So, just add the code above at the top of your config/environment.rb, and
you should be all set and warning-free. I hope this helps someone.