[bug]xml declaration "standalone" is missing with JRuby

[ccvs1993]

Please describe the bug

xml declaration "standalone" is missing with JRuby.

Help us reproduce what you're seeing

Here is sample code:

require 'nokogiri'

xml = Nokogiri::XML('<?xml version = "1.0" encoding = "UTF-8" standalone ="no"?>')
puts xml

Expected behavior

The output should be

<?xml version="1.0" encoding="UTF-8" standalone="no"?>

And I can also see this output with CRuby.

However, I got output with JRuby:

<?xml version="1.0" encoding="UTF-8"?>

Environment

jruby 9.4.3.0 (3.1.4) 2023-06-07 3086960792 OpenJDK 64-Bit Server VM 25.352-b08 on 1.8.0_352-8u352-ga-1~18.04-b08 +jit [x86_64-linux]
Nokogiri version: nokogiri-1.15.3-java

[flavorjones]

@ccvs1993 Thank you for reporting this! After a brief investigation, I've confirmed that the standalone attribute is simply missing from the JRuby implementation's declaration serialization. It shouldn't be hard to fix, and I'll schedule some time to look into it.