Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.ComponentModel.DataAnnotations/DataAnnotations/AppSettings.cs

@@ -0,0 +1,52 @@
+//------------------------------------------------------------------------------
+// <copyright file="AppSettings.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>
+//------------------------------------------------------------------------------
+
+// AppSettings.cs
+//
+
+using System;
+using System.Collections.Specialized;
+using System.Configuration;
+using System.Diagnostics.CodeAnalysis;
+
+namespace System.ComponentModel.DataAnnotations {
+    internal static class AppSettings {
+#if MONO
+        internal static readonly bool DisableRegEx = false;
+#else
+        private static volatile bool _settingsInitialized = false;
+        private static object _appSettingsLock = new object();
+        private static void EnsureSettingsLoaded() {
+            if (!_settingsInitialized) {
+                lock (_appSettingsLock) {
+                    if (!_settingsInitialized) {
+                        NameValueCollection settings = null;
+
+                        try {
+                            settings = ConfigurationManager.AppSettings;
+                        }
+                        catch (ConfigurationErrorsException) { }
+                        finally {
+                            if (settings == null || !Boolean.TryParse(settings["dataAnnotations:dataTypeAttribute:disableRegEx"], out _disableRegEx))
+                                _disableRegEx = false;
+
+                            _settingsInitialized = true;
+                        }
+                    }
+                }
+            }
+        }
+
+        private static bool _disableRegEx;
+        internal static bool DisableRegEx {
+            get {
+                EnsureSettingsLoaded();
+                return _disableRegEx;
+            }
+        }
+#endif
+    }
+}