fix: Node#dup adds the new node to the document's node cache (#3363)

**What problem is this PR intended to solve?**

`Node#dup` adds the new node to the document's node cache to make sure
it's marked properly. Fixes #3359.

Also, we make sure the new node is decorated if necessary with its
document's decorators.


**Have you included adequate test coverage?**

Yes! HUGE thanks to @byroot for doing the work to create a tight
reproduction. 🙇


**Does this change affect the behavior of either the C or the Java
implementations?**

Both bugfixes affect the C implementation only.

ext/nokogiri/xml_node.c

@@ -969,6 +969,7 @@ rb_xml_node_initialize_copy_with_args(VALUE rb_self, VALUE rb_other, VALUE rb_le
   xmlNodePtr c_self, c_other;
   int c_level;
   xmlDocPtr c_new_parent_doc;
+  VALUE rb_node_cache;
 
   Noko_Node_Get_Struct(rb_other, xmlNode, c_other);
   c_level = (int)NUM2INT(rb_level);
@@ -980,6 +981,10 @@ rb_xml_node_initialize_copy_with_args(VALUE rb_self, VALUE rb_other, VALUE rb_le
   _xml_node_data_ptr_set(rb_self, c_self);
   noko_xml_document_pin_node(c_self);
 
+  rb_node_cache = DOC_NODE_CACHE(c_new_parent_doc);
+  rb_ary_push(rb_node_cache, rb_self);
+  rb_funcall(rb_new_parent_doc, id_decorate, 1, rb_self);
+
   return rb_self;
 }
 

test/xml/test_document_fragment.rb

@@ -301,6 +301,20 @@ def test_dup_creates_tree_with_identical_structure
           assert_equal(original.to_html, duplicate.to_html)
         end
 
+        def test_dup_creates_tree_with_identical_structure_stress
+          # https://github.com/sparklemotion/nokogiri/issues/3359
+          skip_unless_libxml2("this is testing CRuby GC behavior")
+
+          original = Nokogiri::XML::DocumentFragment.parse("<div><p>hello</p></div>")
+          duplicate = original.dup
+
+          stress_memory_while do
+            duplicate.to_html
+          end
+
+          assert_equal(original.to_html, duplicate.to_html)
+        end
+
         def test_dup_creates_mutable_tree
           original = Nokogiri::XML::DocumentFragment.parse("<div><p>hello</p></div>")
           duplicate = original.dup

test/xml/test_node.rb

@@ -243,15 +243,20 @@ def test_dup_different_parent_document
           doc1 = XML::Document.parse("<root><div><p>hello</p></div></root>")
           doc2 = XML::Document.parse("<div></div>")
 
+          x = Module.new { def awesome!; end }
+          doc2.decorators(XML::Node) << x
+          doc2.decorate!
+
           div = doc1.at_css("div")
           copy = div.dup(1, doc2)
 
           assert_same(doc2, copy.document)
-          assert_equal(1, copy.children.length) # deep copy
+          assert_equal(1, copy.children.length, "expected a deep copy")
+          assert_respond_to(copy, :awesome!, "expected decorators to be copied")
 
           copy = div.dup(0, doc2)
 
-          assert_equal(0, copy.children.length) # shallow copy
+          assert_equal(0, copy.children.length, "expected a shallow copy")
         end
 
         def test_subclass_dup