Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Xml/System/Xml/Schema/Chameleonkey.cs

@@ -0,0 +1,69 @@
+//------------------------------------------------------------------------------
+// <copyright file="XmlSchemaExternal.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>
+// <owner current="true" primary="true">[....]</owner>                                                                 
+//------------------------------------------------------------------------------
+
+namespace System.Xml.Schema {
+
+    using System.Collections;
+    using System.ComponentModel;
+    using System.Diagnostics;
+    using System.Xml.Serialization;
+
+    // Case insensitive file name key for use in a hashtable.
+
+    internal class ChameleonKey {
+        internal string targetNS;
+        internal Uri chameleonLocation;
+        // Original schema (used for reference equality only)
+        //   stored only when the chameleonLocation is an empty URI in which case the location
+        //   is not a good enough identification of the schema
+        internal XmlSchema originalSchema;
+        int hashCode;
+
+        /// <summary>
+        /// Creates a new chameleon key - an identification for a chameleon schema instance
+        /// </summary>
+        /// <param name="ns">The target namespace of the instance of the chameleon schema</param>
+        /// <param name="originalSchema">The original (chameleon) schema (the one without the target namespace).
+        ///   This is used to get the location (base uri) and to identify the schema.</param>
+        public ChameleonKey(string ns, XmlSchema originalSchema) {
+            targetNS = ns;
+            chameleonLocation = originalSchema.BaseUri;
+            if (chameleonLocation.OriginalString.Length == 0) {
+                // Only store the original schema when the location is empty URI
+                //   by doing this we effectively allow multiple chameleon schemas for the same target namespace
+                //   and URI, but that only makes sense for empty URI (not specified)
+                this.originalSchema = originalSchema;
+            }
+        }
+        
+        public override int GetHashCode() {
+            if (hashCode == 0) {
+                hashCode = targetNS.GetHashCode() + chameleonLocation.GetHashCode() +
+                    (originalSchema == null ? 0 : originalSchema.GetHashCode());
+            }
+            return hashCode;
+        }
+
+        public override bool Equals(object obj) {
+            if (Ref.ReferenceEquals(this,obj)) {
+                return true;
+            }
+            ChameleonKey cKey = obj as ChameleonKey;
+            if (cKey != null) {
+                // We want to compare the target NS and the schema location. 
+                // If the location is empty (but only then) we also want to compare the original schema instance.
+                // As noted above the originalSchema is null if the chameleonLocation is non-empty. As a result we
+                // can simply compare the reference to the original schema always (regardless of the schemalocation).
+                Debug.Assert((chameleonLocation.OriginalString.Length == 0 && originalSchema != null)
+                    || (chameleonLocation.OriginalString.Length != 0 && originalSchema == null));
+                return this.targetNS.Equals(cKey.targetNS) && this.chameleonLocation.Equals(cKey.chameleonLocation) &&
+                    Ref.ReferenceEquals(originalSchema, cKey.originalSchema);
+            }
+            return false;
+        }
+    }
+}