feat/fix: introduce Document#namespace_inheritance attr

When true, reparented elements without a namespace will inherit their
new parent's namespace (if one exists). Defaults to +false+.

This is part of addressing the behavior change introduced in v1.12 by
1f483f0, allowing us to switch it on or off per-document. See #2317.

ext/java/nokogiri/XmlDocumentFragment.java

@@ -34,8 +34,6 @@
 public class XmlDocumentFragment extends XmlNode
 {
 
-  private XmlElement fragmentContext;
-
   public
   XmlDocumentFragment(Ruby ruby)
   {
@@ -75,10 +73,6 @@ public class XmlDocumentFragment extends XmlNode
     fragment.setDocument(context, doc);
     fragment.setNode(context.runtime, doc.getDocument().createDocumentFragment());
 
-    //TODO: Get namespace definitions from doc.
-    if (args.length == 3 && args[2] != null && args[2] instanceof XmlElement) {
-      fragment.fragmentContext = (XmlElement)args[2];
-    }
     Helpers.invoke(context, fragment, "initialize", args);
     return fragment;
   }
@@ -158,12 +152,6 @@ public class XmlDocumentFragment extends XmlNode
     return null;
   }
 
-  public XmlElement
-  getFragmentContext()
-  {
-    return fragmentContext;
-  }
-
   @Override
   public void
   relink_namespace(ThreadContext context)

ext/java/nokogiri/XmlNode.java

@@ -12,6 +12,7 @@
 import org.apache.xerces.dom.CoreDocumentImpl;
 import org.jruby.Ruby;
 import org.jruby.RubyArray;
+import org.jruby.RubyBoolean;
 import org.jruby.RubyClass;
 import org.jruby.RubyFixnum;
 import org.jruby.RubyInteger;
@@ -421,7 +422,14 @@ public class XmlNode extends RubyObject
     String nsURI = e.lookupNamespaceURI(prefix);
     this.node = NokogiriHelpers.renameNode(e, nsURI, e.getNodeName());
 
-    if (nsURI == null || nsURI.isEmpty()) { return; }
+    if (nsURI == null || nsURI.isEmpty()) {
+      RubyBoolean ns_inherit =
+        (RubyBoolean)document(context.runtime).getInstanceVariable("@namespace_inheritance");
+      if (ns_inherit.isTrue()) {
+        set_namespace(context, ((XmlNode)parent(context)).namespace(context));
+      }
+      return;
+    }
 
     String currentPrefix = e.getParentNode().lookupPrefix(nsURI);
     String currentURI = e.getParentNode().lookupNamespaceURI(prefix);
@@ -1743,24 +1751,11 @@ protected enum AdoptScheme {
       e.appendChild(otherNode);
       otherNode = e;
     } else {
-      addNamespaceURIIfNeeded(otherNode);
       parent.appendChild(otherNode);
     }
     return new Node[] { otherNode };
   }
 
-  private void
-  addNamespaceURIIfNeeded(Node child)
-  {
-    if (this instanceof XmlDocumentFragment && ((XmlDocumentFragment) this).getFragmentContext() != null) {
-      XmlElement fragmentContext = ((XmlDocumentFragment) this).getFragmentContext();
-      String namespace_uri = fragmentContext.node.getNamespaceURI();
-      if (namespace_uri != null && namespace_uri.length() > 0) {
-        NokogiriHelpers.renameNode(child, namespace_uri, child.getNodeName());
-      }
-    }
-  }
-
   protected void
   adoptAsPrevSibling(ThreadContext context,
                      Node parent,

ext/nokogiri/xml_node.c

@@ -69,6 +69,13 @@ relink_namespace(xmlNodePtr reparented)
   /* Avoid segv when relinking against unlinked nodes. */
   if (reparented->type != XML_ELEMENT_NODE || !reparented->parent) { return; }
 
+  /* Make sure that our reparented node has the correct namespaces */
+  if (!reparented->ns &&
+      (reparented->doc != (xmlDocPtr)reparented->parent) &&
+      (rb_iv_get(DOC_RUBY_OBJECT(reparented->doc), "@namespace_inheritance") == Qtrue)) {
+    xmlSetNs(reparented, reparented->parent->ns);
+  }
+
   /* Search our parents for an existing definition */
   if (reparented->nsDef) {
     xmlNsPtr curr = reparented->nsDef;

lib/nokogiri/xml/document.rb

@@ -113,9 +113,55 @@ def self.parse string_or_io, url = nil, encoding = nil, options = ParseOptions::
       # A list of Nokogiri::XML::SyntaxError found when parsing a document
       attr_accessor :errors
 
+      # When true, reparented elements without a namespace will inherit their new parent's
+      # namespace (if one exists). Defaults to +false+.
+      #
+      # @example Default behavior of namespace inheritance
+      #   xml = <<~EOF
+      #           <root xmlns:foo="http://nokogiri.org/default_ns/test/foo">
+      #             <foo:parent>
+      #             </foo:parent>
+      #           </root>
+      #         EOF
+      #   doc = Nokogiri::XML(xml)
+      #   parent = doc.at_xpath("//foo:parent", "foo" => "http://nokogiri.org/default_ns/test/foo")
+      #   parent.add_child("<child></child>")
+      #   doc.to_xml
+      #   # => <?xml version="1.0"?>
+      #   #    <root xmlns:foo="http://nokogiri.org/default_ns/test/foo">
+      #   #      <foo:parent>
+      #   #        <child/>
+      #   #      </foo:parent>
+      #   #    </root>
+      #
+      # @example Setting namespace inheritance to +true+
+      #   xml = <<~EOF
+      #           <root xmlns:foo="http://nokogiri.org/default_ns/test/foo">
+      #             <foo:parent>
+      #             </foo:parent>
+      #           </root>
+      #         EOF
+      #   doc = Nokogiri::XML(xml)
+      #   doc.namespace_inheritance = true
+      #   parent = doc.at_xpath("//foo:parent", "foo" => "http://nokogiri.org/default_ns/test/foo")
+      #   parent.add_child("<child></child>")
+      #   doc.to_xml
+      #   # => <?xml version="1.0"?>
+      #   #    <root xmlns:foo="http://nokogiri.org/default_ns/test/foo">
+      #   #      <foo:parent>
+      #   #        <foo:child/>
+      #   #      </foo:parent>
+      #   #    </root>
+      #
+      # @return [Boolean]
+      #
+      # @since v1.12.4
+      attr_accessor :namespace_inheritance
+
       def initialize *args # :nodoc:
         @errors     = []
         @decorators = nil
+        @namespace_inheritance = false
       end
 
       ##

test/xml/test_document.rb

@@ -15,6 +15,13 @@ class TestDocument < Nokogiri::TestCase
 
         let(:xml) { Nokogiri::XML.parse(File.read(XML_FILE), XML_FILE) }
 
+        def test_default_namespace_inheritance
+          doc = Nokogiri::XML::Document.new
+          refute(doc.namespace_inheritance)
+          doc.namespace_inheritance = true
+          assert(doc.namespace_inheritance)
+        end
+
         def test_dtd_with_empty_internal_subset
           doc = Nokogiri::XML(<<~eoxml)
             <?xml version="1.0"?>

test/xml/test_node_reparenting.rb

@@ -557,6 +557,37 @@ def coerce(data)
               end
             end
           end
+
+          describe "given a parent node with a non-default namespace" do
+            let(:doc) do
+              Nokogiri::XML(<<~EOF)
+                <root xmlns:foo="http://nokogiri.org/default_ns/test/foo">
+                  <foo:parent>
+                  </foo:parent>
+                </root>
+              EOF
+            end
+            let(:parent) { doc.at_xpath("//foo:parent", "foo" => "http://nokogiri.org/default_ns/test/foo") }
+
+            describe "and namespace_inheritance is off" do
+              it "inserts a child node that does not inherit the parent's namespace" do
+                refute(doc.namespace_inheritance)
+                child = parent.add_child("<child></child>").first
+                puts doc.to_xml
+                puts child.namespace.inspect
+                assert_nil(child.namespace)
+              end
+            end
+
+            describe "and namespace_inheritance is on" do
+              it "inserts a child node that inherits the parent's namespace" do
+                doc.namespace_inheritance = true
+                child = parent.add_child("<child></child>").first
+                assert_not_nil(child.namespace)
+                assert_equal("http://nokogiri.org/default_ns/test/foo", child.namespace.href)
+              end
+            end
+          end
         end
 
         describe "#add_previous_sibling" do