If I understand this correctly, the original issue was fixed in #5627 and the CGI tweak was partly reverted in 3d8847e . Is it safe to use the CGIEscape.java library now? I didn't find any issues and the CI is green. ping @headius ?

Looking into it. I want to understand what it was disabled.

I attempted to uncomment both of those lines and that results in errors like this during test/mri/cgi tests:

CGIUtilTest#test_cgi_unescapeHTML:UTF-32LE:
NoMethodError: super: no superclass method `unescapeHTML' for CGI:Class
Did you mean?  unescape_html
               escape_html
               unescapeHTML
               escapeHTML
    org/jruby/RubyBasicObject.java:1709:in `method_missing'
    org/jruby/ext/cgi/escape/CGIEscape.java:377:in `unescapeHTML'
    org/jruby/ext/cgi/escape/CGIEscape.java:377:in `unescapeHTML'
    /Users/headius/projects/jruby/test/mri/cgi/test_cgi_util.rb:135:in `block in CGIUtilTest'

And the issue in #4678 still causes a similar error attempting to call a super foo. Will poke at this a bit but it may be a deeper problem than we can fix for 9.2.9 on short notice.

ok, if it's too risky, feel free to postpone it

Yeah I'll postpone it. There's something not right about how we're putting this particular class hierarchy together, or else something wrong with the way super searches that hierarchy. I'll prioritize this for 9.2.10 so we can get rid of the remaining hacks and workarounds.

I realized a simple way we can integrate this: implement it as a separate ext that does not have to be prepended and supered in the ways MRI does. Looking into this quickly as an option.