Imported Upstream version 3.6.0

Former-commit-id: da6be194a6b1221998fc28233f2503bd61dd9d14

external/aspnetwebstack/src/System.Web.WebPages/TemplateStack.cs

@@ -0,0 +1,61 @@
+// Copyright (c) Microsoft Corporation. All rights reserved. See License.txt in the project root for license information.
+
+using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
+using System.Linq;
+
+namespace System.Web.WebPages
+{
+    /// <summary>
+    /// Template stacks store a stack of template files. WebPageExecutingBase implements this type, so when executing Plan9 or Mvc WebViewPage,
+    /// the stack would contain instances of the page. 
+    /// The stack can be queried to identify properties of the current executing file such as the virtual path of the file.
+    /// </summary>
+    [SuppressMessage("Microsoft.Naming", "CA1711:IdentifiersShouldNotHaveIncorrectSuffix", Justification = "TemplateStack is a stack")]
+    public static class TemplateStack
+    {
+        private static readonly object _contextKey = new object();
+
+        public static ITemplateFile GetCurrentTemplate(HttpContextBase httpContext)
+        {
+            if (httpContext == null)
+            {
+                throw new ArgumentNullException("httpContext");
+            }
+            return GetStack(httpContext).FirstOrDefault();
+        }
+
+        public static ITemplateFile Pop(HttpContextBase httpContext)
+        {
+            if (httpContext == null)
+            {
+                throw new ArgumentNullException("httpContext");
+            }
+            return GetStack(httpContext).Pop();
+        }
+
+        public static void Push(HttpContextBase httpContext, ITemplateFile templateFile)
+        {
+            if (templateFile == null)
+            {
+                throw new ArgumentNullException("templateFile");
+            }
+            if (httpContext == null)
+            {
+                throw new ArgumentNullException("httpContext");
+            }
+            GetStack(httpContext).Push(templateFile);
+        }
+
+        private static Stack<ITemplateFile> GetStack(HttpContextBase httpContext)
+        {
+            var stack = httpContext.Items[_contextKey] as Stack<ITemplateFile>;
+            if (stack == null)
+            {
+                stack = new Stack<ITemplateFile>();
+                httpContext.Items[_contextKey] = stack;
+            }
+            return stack;
+        }
+    }
+}