JRuby on re-homing a default-namespaced node, preserves namespace but does not reflect in xmlns attrib, inconsistent with MRI

[jrochkind]

MRI nokogiri version

$ nokogiri -v
# Nokogiri (1.8.3)
    ---
    warnings: []
    nokogiri: 1.8.3
    ruby:
      version: 2.5.1
      platform: x86_64-darwin16
      description: ruby 2.5.1p57 (2018-03-29 revision 63029) [x86_64-darwin16]
      engine: ruby
    libxml:
      binding: extension
      source: packaged
      libxml2_path: "/Users/jrochkind/.gem/ruby/2.5.1/gems/nokogiri-1.8.3/ports/x86_64-apple-darwin16.7.0/libxml2/2.9.8"
      libxslt_path: "/Users/jrochkind/.gem/ruby/2.5.1/gems/nokogiri-1.8.3/ports/x86_64-apple-darwin16.7.0/libxslt/1.1.32"
      libxml2_patches:
      - 0001-Revert-Do-not-URI-escape-in-server-side-includes.patch
      libxslt_patches: []
      compiled: 2.9.8
      loaded: 2.9.8

Jruby nokogiri version

$ nokogiri -v
Ignoring jruby-launcher-1.1.5-java because its extensions are not built. Try: gem pristine jruby-launcher --version 1.1.5
# Nokogiri (1.8.3)
    ---
    warnings: []
    nokogiri: 1.8.3
    ruby:
      version: 2.5.0
      platform: java
      description: jruby 9.2.0.0 (2.5.0) 2018-05-24 81156a8 Java HotSpot(TM) 64-Bit Server
        VM 25.121-b13 on 1.8.0_121-b13 +jit [darwin-x86_64]
      engine: jruby
      jruby: 9.2.0.0
    xerces: Xerces-J 2.11.0
    nekohtml: NekoHTML 1.9.21

reproduction

require 'nokogiri'

xml_src = <<-EOF
  <top xmlns="http://example.org/top/default">
      <inside>
        value
      </inside>
  </top>
EOF

doc = Nokogiri::XML.parse(xml_src)

new_doc = Nokogiri::XML::Document.new

inside_node = doc.at_xpath("//default:inside", default: "http://example.org/top/default")

puts "inside_node.namespace.href: #{inside_node.namespace.href}"
# in both, it knows this node is in the declared namespace:
#
# MRI   => "http://example.org/top/default"
# JRuby => "http://example.org/top/default"


new_doc.root = inside_node

puts "new_doc.root.namespace.href: #{inside_node.namespace.href}"
# in both, it still knows the node, now in new doc, is in a namespace if you ask:
#
# MRI   => "http://example.org/top/default"
# Jruby => "http://example.org/top/default"

puts "new_doc.to_xml: #{new_doc.to_xml}"
# In MRI if you serialize it to XML, the namespace it is in is an xmlns attrib
#
# <inside xmlns="http://example.org/top/default">
#         value
#       </inside>
#
# In Jruby it is not:
#
# <?xml version="1.0"?>
# <inside>
#         value
#       </inside>

puts "new_doc.at_xpath('//inside') " +
  (new_doc.at_xpath('//inside') ? "present" : "absent")
# In MRI, can't find it without a prefix, it really is in a namespace.
# In MRI => "absent"
#
# In Jruby, the same: "absent", JRuby really does treat it like it's in a namespace

puts "new_doc.at_xpath('//default:inside', default: 'http://example.org/top/default') " +
  (new_doc.at_xpath('//default:inside', default: 'http://example.org/top/default') ? "present" : "absent")
# In MRI can find it with the right namespace
# In MRI =>  "present"
# In Jruby => "present"
# Jruby really does treat it as in that namespace, just doesn't serialize it accordingly

So in JRuby, doing Nokogiri::XML.parse(new_doc.to_xml) would actually result in a different internal document as it would lose the namespace. In MRI, it would be round-trippable.

[flavorjones]

@jrochkind Thanks for the thorough bug report.

[jrochkind]

This seems possibly related to #1469.

Except, if I'm reading that code correctly (I have not executed it), I believe MRI Nokogiri is already doing what the issue-opener there is asking for (which I agree is correct and consistent with best practices exhibited by other top-of-the-line XML libraries), just not in JRuby. Maybe it changed (accidentally?) in between then and now in MRI, but not JRuby?

But I haven't excecuted that code in #1469 or totally wrapped my head around it, it could be a slightly different case.

[jvshahid]

Fixed in #1778. I would like someone to review the newly added tests to make sure they are idiomatic and make sense.