From 46a3c7de1310072d6d68ab992c70b3dd588d94c8 Mon Sep 17 00:00:00 2001
From: Mike Dalessio <mike.dalessio@gmail.com>
Date: Sun, 28 Jan 2018 23:59:33 -0500
Subject: [PATCH] DocumentFragment#dup avoids unnecessary copies.

[fixes #1063]
---
 CHANGELOG.md                          |  1 +
 lib/nokogiri/xml/document_fragment.rb |  9 +++++++++
 test/xml/test_document_fragment.rb    | 14 ++++++++++++++
 3 files changed, 24 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 03093ae4ebf..d25a66ec195 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -104,6 +104,7 @@ If you're offended by what happened here, I'd kindly ask that you comment on the
 * [MRI] OpenBSD installation should be a bit easier now. [#1685] (Thanks, @jeremyevans!)
 * [MRI] Cross-built Windows gems now support Ruby 2.5
 * Node#dup supports copying a node directly to a new document. See the method documentation for details.
+* [MRI] DocumentFragment#dup is now more memory-efficient, avoiding making unnecessary copies. [#1063]
 
 
 ## Bug fixes
diff --git a/lib/nokogiri/xml/document_fragment.rb b/lib/nokogiri/xml/document_fragment.rb
index c2c5bec7350..57c266179d4 100644
--- a/lib/nokogiri/xml/document_fragment.rb
+++ b/lib/nokogiri/xml/document_fragment.rb
@@ -25,6 +25,15 @@ def initialize document, tags = nil, ctx = nil
         children.each { |child| child.parent = self }
       end
 
+      def dup
+        new_document = document.dup
+        new_fragment = XML::DocumentFragment.new(new_document)
+        children.each do |child|
+          child.dup(1, new_document).parent = new_fragment
+        end
+        new_fragment
+      end
+
       ###
       # return the name for DocumentFragment
       def name
diff --git a/test/xml/test_document_fragment.rb b/test/xml/test_document_fragment.rb
index c919ee2068f..3ff801e847d 100644
--- a/test/xml/test_document_fragment.rb
+++ b/test/xml/test_document_fragment.rb
@@ -263,6 +263,20 @@ def test_issue_1077_parsing_of_frozen_strings
         Nokogiri::XML::DocumentFragment.parse(input) # assert_nothing_raised
       end
 
+      def test_dup_creates_tree_with_identical_structure
+        original = Nokogiri::XML::DocumentFragment.parse("<div><p>hello</p></div>")
+        duplicate = original.dup
+        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
+        duplicate.at_css("div").add_child("<b>hello there</b>")
+        assert_nil original.at_css("b")
+        assert_not_nil duplicate.at_css("b")
+      end
+
       if Nokogiri.uses_libxml?
         def test_for_libxml_in_context_fragment_parsing_bug_workaround
           10.times do