Using Ruby 2.7 the following will be printed out:

  /home/aperez/WebKit/Source/JavaScriptCore/offlineasm/parser.rb:631:
  warning: deprecated Object#=~ is called on Annotation; it always returns nil

This is caused by the following change in Ruby:

  https://svn.ruby-lang.org/cgi-bin/viewvc.cgi?revision=65989&view=revision

I see that the Annotation class does *not* define an overload for the =~ operator,
so previously applying it to an Annotation instance was already returning “nil”
(but silently).

Therefore I *think* that swapping the checks in the code to something like

  if @tokens[@idx].is_a? Annotation
     # ...
  elsif (@idx == @tokens.length and not final) or (final and @tokens[@idx] =~ final)
     # ...

should both silence the warning and still be correct.

Note that I do not have much experience with Ruby, nor with modifying offlineasm,
so suggestions are definitely welcome.