Add namespace attributes when necessary

* ext/java/nokogiri/XmlNode.java (relink_namespace): Add a namespace attribute
  to the new adopted node, if the current scope namespace URI or prefix don't
  match the new node's namespace.

Fixes #1774

ext/java/nokogiri/XmlNode.java

@@ -472,10 +472,31 @@ public void relink_namespace(ThreadContext context) {
         String nsURI = e.lookupNamespaceURI(prefix);
         this.node = NokogiriHelpers.renameNode(e, nsURI, e.getNodeName());
 
-        if (nsURI == null || nsURI.isEmpty()) {
+        if (nsURI == null || nsURI == "") {
             return;
         }
 
+        String currentPrefix = e.getParentNode().lookupPrefix(nsURI);
+        String currentURI = e.getParentNode().lookupNamespaceURI(prefix);
+        boolean isDefault = e.getParentNode().isDefaultNamespace(nsURI);
+
+        // add xmlns attribute if this is a new root node or if the node's
+        // namespace isn't a default namespace in the new document
+        if (e.getParentNode().getNodeType() == Node.DOCUMENT_NODE) {
+          // this is the root node, so we must set the namespaces attributes
+          // anyway
+          e.setAttribute(prefix == null ? "xmlns":"xmlns:"+prefix, nsURI);
+        } else if (prefix == null) {
+           if (!isDefault)
+             // this is a default namespace but isn't the default where this
+             // node is being added
+             e.setAttribute("xmlns", nsURI);
+        } else if (currentPrefix != prefix || currentURI != nsURI) {
+          // this is a prefixed namespace but doens't have the same prefix or
+          // the prefix is set to a diffent URI
+          e.setAttribute("xmlns:"+prefix, nsURI);
+        }
+
         if (e.hasAttributes()) {
             NamedNodeMap attrs = e.getAttributes();
 

test/xml/test_node_reparenting.rb

@@ -224,6 +224,59 @@ class TestNodeReparenting < Nokogiri::TestCase
               node.add_child(child)
               assert @doc.at('//xmlns:second')
             end
+
+            describe "and a child node was added to a new doc with the a different namespace using the same prefix" do
+              before do
+                @doc = Nokogiri::XML %Q{<root xmlns:bar="http://tenderlovemaking.com/"><bar:first/></root>}
+                new_doc = Nokogiri::XML %Q{<newroot xmlns:bar="http://flavorjon.es/"/>}
+                assert node = @doc.at("//tenderlove:first", tenderlove: "http://tenderlovemaking.com/")
+                new_doc.root.add_child node
+                @doc = new_doc
+              end
+
+              it "serializes the doc with the proper default namespace" do
+                assert_match /<bar:first\ xmlns:bar="http:\/\/tenderlovemaking.com\/"\/>/, @doc.to_xml
+              end
+            end
+
+            describe "and a child node was added to a new doc with the same default namespaces" do
+              before do
+                new_doc = Nokogiri::XML %Q{<newroot xmlns="http://tenderlovemaking.com/"/>}
+                assert node = @doc.at("//tenderlove:first", tenderlove: "http://tenderlovemaking.com/")
+                new_doc.root.add_child node
+                @doc = new_doc
+              end
+
+              it "serializes the doc with the proper default namespace" do
+                assert_match /<first>/, @doc.to_xml
+              end
+            end
+
+            describe "and a child node was added to a new doc without any default namespaces" do
+              before do
+                new_doc = Nokogiri::XML "<newroot/>"
+                assert node = @doc.at("//tenderlove:first", tenderlove: "http://tenderlovemaking.com/")
+                new_doc.root.add_child node
+                @doc = new_doc
+              end
+
+              it "serializes the doc with the proper default namespace" do
+                assert_match /<first xmlns=\"http:\/\/tenderlovemaking.com\/\">/, @doc.to_xml
+              end
+            end
+
+            describe "and a child node became the root of a new doc" do
+              before do
+                new_doc = Nokogiri::XML::Document.new
+                assert node = @doc.at("//tenderlove:first", tenderlove: "http://tenderlovemaking.com/")
+                new_doc.root = node
+                @doc = new_doc
+              end
+
+              it "serializes the doc with the proper default namespace" do
+                assert_match /<first xmlns=\"http:\/\/tenderlovemaking.com\/\">/, @doc.to_xml
+              end
+            end
           end
 
           describe "given a parent node with a default and non-default namespace" do