[bug] JRuby: reparenting a node does not apply the parent's default namespace

[johnnyshields]

The JRuby parser has a bug where default namespaces on child elements are reverted to the root node's default namesapce, rather than the default namespace of their immediate parent.

Unlike #3455 which was a "syntax preference", this is a bona-fide "bug". The JRuby-parsed and out XML is semantically different than the MRI-parsed one, in a way that can break consumers.

    it 'handles nested default namespaces' do
      doc = Nokogiri::XML::Builder.new do |xml|
        xml.root(xmlns: 'http://outer-namespace.org/') do
          xml.outer('in outer namespace')
          xml.inner(xmlns: 'http://inner-namespace.org/') do
            xml.element('in inner namespace')
          end
          xml.another('back in outer namespace')
        end
      end.doc.to_xml(save_with: Nokogiri::XML::Node::SaveOptions::AS_XML)

      assert_includes(doc, '<root xmlns="http://outer-namespace.org/">')
      assert_includes(doc, '<outer>in outer namespace</outer>')
      assert_includes(doc, '<inner xmlns="http://inner-namespace.org/">')
      # TODO: THE NEXT LINE FAILS ON JRUBY!!
      assert_includes(doc, '<element>in inner namespace</element>')
      # TODO: THE NEXT LINE PASSES ON JRUBY, BUT SHOULD FAIL!!
      # assert_includes(doc, '<element xmlns="http://outer-namespace.org/">in inner namespace</element>')
      assert_includes(doc, '<another>back in outer namespace</another>')
    end

This PR includes test cases which cover this issue: #3456. They are made to pass for now using if Nokogiri.jruby?

[flavorjones]

I alluded to this in my review of #3456 but if we're not testing Builder behavior, I'd prefer to write this test as a simple parse of an input string:

    it 'handles nested default namespaces' do
      doc = Nokogiri::XML::Document.parse(<<~XML).to_xml(save_with: Nokogiri::XML::Node::SaveOptions::AS_XML)
        <root xmlns="http://outer-namespace.org/">
          <outer>in outer namespace</outer>
          <inner xmlns="http://inner-namespace.org/">
            <element>in inner namespace</element>
          </inner>
          <another>back in outer namespace</another>
        </root>
      XML

      assert_includes(doc, '<root xmlns="http://outer-namespace.org/">')
      assert_includes(doc, '<outer>in outer namespace</outer>')
      assert_includes(doc, '<inner xmlns="http://inner-namespace.org/">')
      # TODO: THE NEXT LINE FAILS ON JRUBY!!
      assert_includes(doc, '<element>in inner namespace</element>')
      # TODO: THE NEXT LINE PASSES ON JRUBY, BUT SHOULD FAIL!!
      # assert_includes(doc, '<element xmlns="http://outer-namespace.org/">in inner namespace</element>')
      assert_includes(doc, '<another>back in outer namespace</another>')
    end

but when I do this, the test passes on both CRuby and JRuby. My point here is that writing the test as simply as possible helps understand where the bug is originating.

In this case, it seems to be a bug in node reparenting (which is how Builder works under the hood), and not a parser bug or a serialization bug.

The most descriptive test I could write for this particular reparenting bug is:

    it "foo" do
      doc = Nokogiri::XML(<<~XML)
        <root xmlns='http://outer-namespace.org'>
          <inner xmlns='http://inner-namespace.org'/>
        </root>
      XML
      
      node = doc.create_element("element")
      doc.root.elements.first.add_child(node)

      assert_equal("http://inner-namespace.org", node.namespace.href)
    end

which passes on CRuby and fails on JRuby.