Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Xml/System/Xml/XPath/Internal/NamespaceQuery.cs

@@ -0,0 +1,68 @@
+//------------------------------------------------------------------------------
+// <copyright file="NamespaceQuery.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>                                                                
+// <owner current="true" primary="true">[....]</owner>
+//------------------------------------------------------------------------------
+
+namespace MS.Internal.Xml.XPath {
+    using System;
+    using System.Xml;
+    using System.Xml.XPath;
+    using System.Diagnostics;
+    using System.Globalization;
+
+    internal sealed class NamespaceQuery : BaseAxisQuery {
+        private bool onNamespace;
+        
+        public NamespaceQuery(Query qyParent, string Name, string Prefix, XPathNodeType Type) : base(qyParent, Name, Prefix, Type) {}
+        private NamespaceQuery(NamespaceQuery other) : base(other) {
+            this.onNamespace = other.onNamespace;
+        }
+
+        public override void Reset() {
+            onNamespace = false;
+            base.Reset();
+        }
+
+        public override XPathNavigator Advance() {
+            while (true) {
+                if (!onNamespace) {
+                    currentNode = qyInput.Advance();
+                    if (currentNode == null) {
+                        return null;
+                    }
+                    position = 0;
+                    currentNode = currentNode.Clone();
+                    onNamespace = currentNode.MoveToFirstNamespace();
+                } else {
+                    onNamespace = currentNode.MoveToNextNamespace();
+                }
+
+                if (onNamespace) {
+                    if (matches(currentNode)) {
+                        position++;
+                        return currentNode;
+                    }
+                }
+            } // while
+        } // Advance
+
+        public override bool matches(XPathNavigator e) {
+            Debug.Assert(e.NodeType == XPathNodeType.Namespace);
+            if (e.Value.Length == 0) {
+                Debug.Assert(e.LocalName.Length == 0, "Only xmlns='' can have empty string as a value");
+                // Namespace axes never returns xmlns='', 
+                // because it's not a NS declaration but rather undeclaration.
+                return false;               
+            }
+            if (NameTest) {
+                return Name.Equals(e.LocalName);
+            } else {
+                return true;
+            }
+        }
+                    
+        public override XPathNodeIterator Clone() { return new NamespaceQuery(this); }
+    }
+}