[gxml] GChildNode next/previouse element sibling using libxml2

[Daniel Espinosa Ortiz <despinosa src gnome org>]

commit 2449699c6537956c287255f1727293824f61e3c5
Author: Daniel Espinosa <esodan gmail com>
Date:   Sat Sep 2 22:27:33 2017 -0500

    GChildNode next/previouse element sibling using libxml2
    
    libxml2 has previous/next_element_sibling methods, so
    using them instead.
    
    One of more Fixes for Bug #785279

 gxml/GHtml.vala         |    1 +
 gxml/GXmlChildNode.vala |   30 ++++++++----------------------
 test/GElementTest.vala  |   31 +++++++++++++++++++++++++++++++
 3 files changed, 40 insertions(+), 22 deletions(-)
---
diff --git a/gxml/GHtml.vala b/gxml/GHtml.vala
index d315ea7..810c3c1 100644
--- a/gxml/GHtml.vala
+++ b/gxml/GHtml.vala
@@ -23,6 +23,7 @@
  */
 
 using Gee;
+using Xml;
 
 namespace GXml {
        /**
diff --git a/gxml/GXmlChildNode.vala b/gxml/GXmlChildNode.vala
index 19de0e3..efef54f 100644
--- a/gxml/GXmlChildNode.vala
+++ b/gxml/GXmlChildNode.vala
@@ -42,32 +42,18 @@ public class GXml.GNonDocumentChildNode : GXml.GChildNode,
   // DomNonDocumentTypeChildNode
   public DomElement? previous_element_sibling {
     owned get {
-      if (parent_node != null) {
-        var i = parent_node.child_nodes.index_of (this);
-        if (i == 0)
-          return null;
-        for (var j = i; j >= 1; j--) {
-          var n = parent_node.child_nodes.item (j - 1);
-          if (n is DomElement)
-                       return n as DomElement;
-        }
-      }
-      return null;
+      if (_node == null) return null;
+      var n = _node->previous_element_sibling ();
+      if (n == null) return null;
+      return new GElement (owner_document as GDocument, n);
     }
   }
   public DomElement? next_element_sibling {
     owned get {
-      if (parent_node != null) {
-        var i = parent_node.child_nodes.index_of (this);
-        if (i == parent_node.child_nodes.length - 1)
-          return null;
-        for (var j = i; j < parent_node.child_nodes.length - 1; j--) {
-          var n = parent_node.child_nodes.item (j + 1);
-          if (n is DomElement)
-            return (DomElement) n;
-        }
-      }
-      return null;
+      if (_node == null) return null;
+      var n = _node->next_element_sibling ();
+      if (n == null) return null;
+      return new GElement (owner_document as GDocument, n);
     }
   }
 }
diff --git a/test/GElementTest.vala b/test/GElementTest.vala
index 139510e..0a9be27 100644
--- a/test/GElementTest.vala
+++ b/test/GElementTest.vala
@@ -157,5 +157,36 @@ class GElementTest : GXmlTest  {
                                        assert_not_reached ();
                                }
                });
+               Test.add_func ("/gxml/gelement/previous_element_sibling", () => {
+                       try {
+                               var doc = new GDocument.from_string ("<root> <child/> <child/></root>");
+                               assert (doc.document_element != null);
+                               assert (doc.document_element.parent_node is GXml.Node);
+                               assert (doc.document_element.parent_node is GXml.Document);
+                               assert (doc.document_element.child_nodes[0] != null);
+                               assert (doc.document_element.child_nodes[0].parent_node != null);
+                               assert (doc.document_element.child_nodes[0].parent_node.node_name == "root");
+                               assert (doc.document_element.child_nodes[0] is DomText);
+                               assert (doc.document_element.child_nodes[1] != null);
+                               assert (doc.document_element.child_nodes[1] is DomElement);
+                               assert (doc.document_element.child_nodes[1].node_name == "child");
+                               assert ((doc.document_element.child_nodes[1] as 
DomElement).next_element_sibling != null);
+                               assert ((doc.document_element.child_nodes[1] as 
DomElement).next_element_sibling is DomElement);
+                               assert ((doc.document_element.child_nodes[1] as 
DomElement).next_element_sibling.node_name == "child");
+                               assert (doc.document_element.child_nodes[2] != null);
+                               assert (doc.document_element.child_nodes[2].parent_node != null);
+                               assert (doc.document_element.child_nodes[2].parent_node.node_name == "root");
+                               assert (doc.document_element.child_nodes[2] is DomText);
+                               assert (doc.document_element.child_nodes[3] != null);
+                               assert (doc.document_element.child_nodes[3] is DomElement);
+                               assert (doc.document_element.child_nodes[3].node_name == "child");
+                               assert ((doc.document_element.child_nodes[3] as 
DomElement).previous_element_sibling != null);
+                               assert ((doc.document_element.child_nodes[3] as 
DomElement).previous_element_sibling is DomElement);
+                               assert ((doc.document_element.child_nodes[3] as 
DomElement).previous_element_sibling.node_name == "child");
+                               } catch (GLib.Error e) {
+                                       Test.message (e.message);
+                                       assert_not_reached ();
+                               }
+               });
        }
 }