Moving the order of generated hidden tags for checkbox to end of the form

- #2994
- Affects both HtmlHelper and TagHelper scenarios
- Checkboxes not enclosed in a form will generate inline hidden tags
- Added necessary properties to FormContext
- Added some functional and unit tests

src/Microsoft.AspNet.Mvc.TagHelpers/InputTagHelper.cs

@@ -278,7 +278,15 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                 if (hiddenForCheckboxTag != null)
                 {
                     hiddenForCheckboxTag.TagRenderMode = renderingMode;
-                    output.Content.Append(hiddenForCheckboxTag);
+
+                    if (ViewContext.FormContext.CanRenderAtEndOfForm)
+                    {
+                        ViewContext.FormContext.EndOfFormContent.Add(hiddenForCheckboxTag);
+                    }
+                    else
+                    {
+                        output.Content.Append(hiddenForCheckboxTag);
+                    }
                 }
             }
         }

src/Microsoft.AspNet.Mvc.TagHelpers/RenderAtEndOfFormTagHelper.cs

@@ -0,0 +1,61 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.ComponentModel;
+using System.Threading.Tasks;
+using Microsoft.AspNet.Mvc.Rendering;
+using Microsoft.AspNet.Mvc.ViewFeatures;
+using Microsoft.AspNet.Razor.Runtime.TagHelpers;
+
+namespace Microsoft.AspNet.Mvc.TagHelpers
+{
+    /// <summary>
+    /// <see cref="ITagHelper"/> implementation targeting all form elements
+    /// to generate content before the form end tag.
+    /// </summary>
+    [EditorBrowsable(EditorBrowsableState.Never)]
+    [HtmlTargetElement("form")]
+    public class RenderAtEndOfFormTagHelper : TagHelper
+    {
+        public override int Order => -1000;
+
+        [HtmlAttributeNotBound]
+        [ViewContext]
+        public ViewContext ViewContext { get; set; }
+
+        /// <inheritdoc />
+        public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
+        {
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
+            if (output == null)
+            {
+                throw new ArgumentNullException(nameof(output));
+            }
+
+            // Push the new FormContext.
+            ViewContext.FormContext = new FormContext
+            {
+                CanRenderAtEndOfForm = true
+            };
+
+            await context.GetChildContentAsync();
+
+            var formContext = ViewContext.FormContext;
+            if (formContext.HasEndOfFormContent)
+            {
+                foreach (var content in formContext.EndOfFormContent)
+                {
+                    output.PostContent.Append(content);
+                }
+            }
+
+            // Reset the FormContext
+            ViewContext.FormContext = null;
+        }
+    }
+}

src/Microsoft.AspNet.Mvc.ViewFeatures/Rendering/MvcForm.cs

@@ -3,6 +3,8 @@
 
 using System;
 using Microsoft.AspNet.Mvc.ViewFeatures;
+using Microsoft.Extensions.WebEncoders;
+using Microsoft.Extensions.DependencyInjection;
 
 namespace Microsoft.AspNet.Mvc.Rendering
 {
@@ -19,9 +21,6 @@ namespace Microsoft.AspNet.Mvc.Rendering
             }
 
             _viewContext = viewContext;
-
-            // Push the new FormContext; GenerateEndForm() does the corresponding pop.
-            _viewContext.FormContext = new FormContext();
         }
 
         public void Dispose()
@@ -40,6 +39,7 @@ namespace Microsoft.AspNet.Mvc.Rendering
 
         protected virtual void GenerateEndForm()
         {
+            RenderEndOfFormContent();
             _viewContext.Writer.Write("</form>");
             _viewContext.FormContext = null;
         }
@@ -52,5 +52,33 @@ namespace Microsoft.AspNet.Mvc.Rendering
                 GenerateEndForm();
             }
         }
+
+        private void RenderEndOfFormContent()
+        {
+            var formContext = _viewContext.FormContext;
+            if (formContext.HasEndOfFormContent)
+            {
+                var writer = _viewContext.Writer;
+                var htmlWriter = writer as HtmlTextWriter;
+
+                IHtmlEncoder htmlEncoder = null;
+                if (htmlWriter == null)
+                {
+                    htmlEncoder = _viewContext.HttpContext.RequestServices.GetRequiredService<IHtmlEncoder>();
+                }
+
+                foreach (var content in formContext.EndOfFormContent)
+                {
+                    if (htmlWriter == null)
+                    {
+                        content.WriteTo(writer, htmlEncoder);
+                    }
+                    else
+                    {
+                        htmlWriter.Write(content);
+                    }
+                }
+            }
+        }
     }
 }

src/Microsoft.AspNet.Mvc.ViewFeatures/ViewFeatures/FormContext.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using Microsoft.AspNet.Html.Abstractions;
 
 namespace Microsoft.AspNet.Mvc.ViewFeatures
 {
@@ -11,6 +12,7 @@ namespace Microsoft.AspNet.Mvc.ViewFeatures
         private readonly Dictionary<string, bool> _renderedFields =
             new Dictionary<string, bool>(StringComparer.Ordinal);
         private Dictionary<string, object> _formData;
+        private IList<IHtmlContent> _endOfFormContent;
 
         /// <summary>
         /// Property bag for any information you wish to associate with a &lt;form/&gt; in an
@@ -29,6 +31,25 @@ namespace Microsoft.AspNet.Mvc.ViewFeatures
             }
         }
 
+        public bool HasFormData => _formData != null;
+
+        public bool HasEndOfFormContent => _endOfFormContent != null;
+
+        public IList<IHtmlContent> EndOfFormContent
+        {
+            get
+            {
+                if (_endOfFormContent == null)
+                {
+                    _endOfFormContent = new List<IHtmlContent>();
+                }
+
+                return _endOfFormContent;
+            }
+        }
+
+        public bool CanRenderAtEndOfForm { get; set; }
+
         public bool RenderedField(string fieldName)
         {
             if (fieldName == null)

src/Microsoft.AspNet.Mvc.ViewFeatures/ViewFeatures/HtmlHelper.cs

@@ -272,12 +272,24 @@ namespace Microsoft.AspNet.Mvc.ViewFeatures
             FormMethod method,
             object htmlAttributes)
         {
+            // Push the new FormContext; MvcForm.GenerateEndForm() does the corresponding pop.
+            _viewContext.FormContext = new FormContext
+            {
+                CanRenderAtEndOfForm = true
+            };
+
             return GenerateForm(actionName, controllerName, routeValues, method, htmlAttributes);
         }
 
         /// <inheritdoc />
         public MvcForm BeginRouteForm(string routeName, object routeValues, FormMethod method, object htmlAttributes)
         {
+            // Push the new FormContext; MvcForm.GenerateEndForm() does the corresponding pop.
+            _viewContext.FormContext = new FormContext
+            {
+                CanRenderAtEndOfForm = true
+            };
+
             return GenerateRouteForm(routeName, routeValues, method, htmlAttributes);
         }
 
@@ -708,13 +720,24 @@ namespace Microsoft.AspNet.Mvc.ViewFeatures
                 isChecked,
                 htmlAttributes);
 
-            var hidden = _htmlGenerator.GenerateHiddenForCheckbox(ViewContext, modelExplorer, expression);
+            var hiddenForCheckboxTag = _htmlGenerator.GenerateHiddenForCheckbox(ViewContext, modelExplorer, expression);
-            if (checkbox == null || hidden == null)
+            if (checkbox == null || hiddenForCheckboxTag == null)
             {
                 return HtmlString.Empty;
             }
 
-            return new BufferedHtmlContent().Append(checkbox).Append(hidden);
+            var checkboxContent = new BufferedHtmlContent().Append(checkbox);
+
+            if (ViewContext.FormContext.CanRenderAtEndOfForm)
+            {
+                ViewContext.FormContext.EndOfFormContent.Add(hiddenForCheckboxTag);
+            }
+            else
+            {
+                checkboxContent.Append(hiddenForCheckboxTag);
+            }
+
+            return checkboxContent;
         }
 
         protected virtual string GenerateDisplayName(ModelExplorer modelExplorer, string expression)

test/Microsoft.AspNet.Mvc.FunctionalTests/compiler/resources/HtmlGenerationWebSite.HtmlGeneration_Home.EmployeeList.html

@@ -24,7 +24,7 @@ EmployeeName_0</textarea>
 </div>
 <div>
     <label class="employee" for="z0__Remote">Remote</label>
-    <input data-val="true" data-val-required="The Remote field is required." id="z0__Remote" name="[0].Remote" type="checkbox" value="true" /><input name="[0].Remote" type="hidden" value="false" />
+    <input data-val="true" data-val-required="The Remote field is required." id="z0__Remote" name="[0].Remote" type="checkbox" value="true" />
 </div>
 <div>
     <label class="employee" for="z0__OfficeNumber">OfficeNumber</label>
@@ -55,7 +55,7 @@ EmployeeName_1</textarea>
 </div>
 <div>
     <label class="employee" for="z1__Remote">Remote</label>
-    <input data-val="true" data-val-required="The Remote field is required." id="z1__Remote" name="[1].Remote" type="checkbox" value="true" /><input name="[1].Remote" type="hidden" value="false" />
+    <input data-val="true" data-val-required="The Remote field is required." id="z1__Remote" name="[1].Remote" type="checkbox" value="true" />
 </div>
 <div>
     <label class="employee" for="z1__OfficeNumber">OfficeNumber</label>
@@ -86,7 +86,7 @@ EmployeeName_2</textarea>
 </div>
 <div>
     <label class="employee" for="z2__Remote">Remote</label>
-    <input checked="checked" data-val="true" data-val-required="The Remote field is required." id="z2__Remote" name="[2].Remote" type="checkbox" value="true" /><input name="[2].Remote" type="hidden" value="false" />
+    <input checked="checked" data-val="true" data-val-required="The Remote field is required." id="z2__Remote" name="[2].Remote" type="checkbox" value="true" />
 </div>
 <div>
     <label class="employee" for="z2__OfficeNumber">OfficeNumber</label>
@@ -94,5 +94,5 @@ EmployeeName_2</textarea>
 <option>1002</option>
 </select>
 </div>            <input type="submit" />
-</form></body>
+<input name="[0].Remote" type="hidden" value="false" /><input name="[1].Remote" type="hidden" value="false" /><input name="[2].Remote" type="hidden" value="false" /></form></body>
 </html>

test/Microsoft.AspNet.Mvc.FunctionalTests/compiler/resources/HtmlGenerationWebSite.HtmlGeneration_Home.Order.Encoded.html

@@ -33,7 +33,7 @@
         </div>
         <div>
             <label class="order" for="HtmlEncode[[NeedSpecialHandle]]">HtmlEncode[[NeedSpecialHandle]]</label>
-            <input checked="HtmlEncode[[checked]]" data-val="HtmlEncode[[true]]" data-val-required="HtmlEncode[[The NeedSpecialHandle field is required.]]" id="HtmlEncode[[NeedSpecialHandle]]" name="HtmlEncode[[NeedSpecialHandle]]" type="HtmlEncode[[checkbox]]" value="HtmlEncode[[true]]" /><input name="HtmlEncode[[NeedSpecialHandle]]" type="HtmlEncode[[hidden]]" value="HtmlEncode[[false]]" />
+            <input checked="HtmlEncode[[checked]]" data-val="HtmlEncode[[true]]" data-val-required="HtmlEncode[[The NeedSpecialHandle field is required.]]" id="HtmlEncode[[NeedSpecialHandle]]" name="HtmlEncode[[NeedSpecialHandle]]" type="HtmlEncode[[checkbox]]" value="HtmlEncode[[true]]" />
         </div>
         <div>
             <label class="order" for="HtmlEncode[[PaymentMethod]]">HtmlEncode[[PaymentMethod]]</label>
@@ -75,6 +75,6 @@
 </ul></div>
         <input type="HtmlEncode[[hidden]]" id="HtmlEncode[[Customer_Key]]" name="HtmlEncode[[Customer.Key]]" value="HtmlEncode[[KeyA]]" />
         <input type="submit" />
-    <input name="HtmlEncode[[__RequestVerificationToken]]" type="HtmlEncode[[hidden]]" value="{0}" /></form>
+    <input name="HtmlEncode[[__RequestVerificationToken]]" type="HtmlEncode[[hidden]]" value="{0}" /><input name="HtmlEncode[[NeedSpecialHandle]]" type="HtmlEncode[[hidden]]" value="HtmlEncode[[false]]" /></form>
 </body>
 </html>

test/Microsoft.AspNet.Mvc.FunctionalTests/compiler/resources/HtmlGenerationWebSite.HtmlGeneration_Home.Order.html

@@ -33,7 +33,7 @@
         </div>
         <div>
             <label class="order" for="NeedSpecialHandle">NeedSpecialHandle</label>
-            <input checked="checked" data-val="true" data-val-required="The NeedSpecialHandle field is required." id="NeedSpecialHandle" name="NeedSpecialHandle" type="checkbox" value="true" /><input name="NeedSpecialHandle" type="hidden" value="false" />
+            <input checked="checked" data-val="true" data-val-required="The NeedSpecialHandle field is required." id="NeedSpecialHandle" name="NeedSpecialHandle" type="checkbox" value="true" />
         </div>
         <div>
             <label class="order" for="PaymentMethod">PaymentMethod</label>
@@ -75,6 +75,6 @@
 </ul></div>
         <input type="hidden" id="Customer_Key" name="Customer.Key" value="KeyA" />
         <input type="submit" />
-    <input name="__RequestVerificationToken" type="hidden" value="{0}" /></form>
+    <input name="__RequestVerificationToken" type="hidden" value="{0}" /><input name="NeedSpecialHandle" type="hidden" value="false" /></form>
 </body>
 </html>

test/Microsoft.AspNet.Mvc.FunctionalTests/compiler/resources/HtmlGenerationWebSite.HtmlGeneration_Home.OrderUsingHtmlHelpers.Encoded.html

@@ -33,7 +33,7 @@
         </div>
         <div>
             <label class="HtmlEncode[[order]]" for="HtmlEncode[[NeedSpecialHandle]]">HtmlEncode[[NeedSpecialHandle]]</label>
-            <input checked="HtmlEncode[[checked]]" data-val="HtmlEncode[[true]]" data-val-required="HtmlEncode[[The NeedSpecialHandle field is required.]]" id="HtmlEncode[[NeedSpecialHandle]]" name="HtmlEncode[[NeedSpecialHandle]]" type="HtmlEncode[[checkbox]]" value="HtmlEncode[[true]]" /><input name="HtmlEncode[[NeedSpecialHandle]]" type="HtmlEncode[[hidden]]" value="HtmlEncode[[false]]" />
+            <input checked="HtmlEncode[[checked]]" data-val="HtmlEncode[[true]]" data-val-required="HtmlEncode[[The NeedSpecialHandle field is required.]]" id="HtmlEncode[[NeedSpecialHandle]]" name="HtmlEncode[[NeedSpecialHandle]]" type="HtmlEncode[[checkbox]]" value="HtmlEncode[[true]]" />
         </div>
         <div>
             <label class="HtmlEncode[[order]]" for="HtmlEncode[[PaymentMethod]]">HtmlEncode[[PaymentMethod]]</label>
@@ -74,5 +74,5 @@
 </ul></div>
         <input id="HtmlEncode[[Customer_Key]]" name="HtmlEncode[[Customer.Key]]" type="HtmlEncode[[hidden]]" value="HtmlEncode[[KeyA]]" />
         <input type="submit"/>
-    <input name="HtmlEncode[[__RequestVerificationToken]]" type="HtmlEncode[[hidden]]" value="{0}" /></form></body>
+    <input name="HtmlEncode[[__RequestVerificationToken]]" type="HtmlEncode[[hidden]]" value="{0}" /><input name="HtmlEncode[[NeedSpecialHandle]]" type="HtmlEncode[[hidden]]" value="HtmlEncode[[false]]" /></form></body>
 </html>

test/Microsoft.AspNet.Mvc.FunctionalTests/compiler/resources/HtmlGenerationWebSite.HtmlGeneration_Home.OrderUsingHtmlHelpers.html

@@ -33,7 +33,7 @@
         </div>
         <div>
             <label class="order" for="NeedSpecialHandle">NeedSpecialHandle</label>
-            <input checked="checked" data-val="true" data-val-required="The NeedSpecialHandle field is required." id="NeedSpecialHandle" name="NeedSpecialHandle" type="checkbox" value="true" /><input name="NeedSpecialHandle" type="hidden" value="false" />
+            <input checked="checked" data-val="true" data-val-required="The NeedSpecialHandle field is required." id="NeedSpecialHandle" name="NeedSpecialHandle" type="checkbox" value="true" />
         </div>
         <div>
             <label class="order" for="PaymentMethod">PaymentMethod</label>
@@ -74,5 +74,5 @@
 </ul></div>
         <input id="Customer_Key" name="Customer.Key" type="hidden" value="KeyA" />
         <input type="submit"/>
-    <input name="__RequestVerificationToken" type="hidden" value="{0}" /></form></body>
+    <input name="__RequestVerificationToken" type="hidden" value="{0}" /><input name="NeedSpecialHandle" type="hidden" value="false" /></form></body>
 </html>

test/Microsoft.AspNet.Mvc.TagHelpers.Test/RenderAtEndOfFormTagHelperTest.cs

@@ -0,0 +1,90 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.AspNet.Mvc.Rendering;
+using Microsoft.AspNet.Razor.Runtime.TagHelpers;
+using Xunit;
+
+namespace Microsoft.AspNet.Mvc.TagHelpers
+{
+    public class RenderAtEndOfFormTagHelperTest
+    {
+        public static TheoryData RenderAtEndOfFormTagHelperData
+        {
+            get
+            {
+                // tagBuilderList, expectedOutput
+                return new TheoryData<List<TagBuilder>, string>
+                {
+                    {
+                        new List<TagBuilder>
+                        {
+                            GetTagBuilder("input", "SomeName", "hidden", "false", TagRenderMode.SelfClosing)
+                        },
+                        @"<input name=""SomeName"" type=""hidden"" value=""false"" />"
+                    },
+                    {
+                        new List<TagBuilder>
+                        {
+                            GetTagBuilder("input", "SomeName", "hidden", "false", TagRenderMode.SelfClosing),
+                            GetTagBuilder("input", "SomeOtherName", "hidden", "false", TagRenderMode.SelfClosing)
+                        },
+                        @"<input name=""SomeName"" type=""hidden"" value=""false"" />" + 
+                        @"<input name=""SomeOtherName"" type=""hidden"" value=""false"" />"
+                    }
+                };
+            }
+        }
+
+        [Theory]
+        [MemberData(nameof(RenderAtEndOfFormTagHelperData))]
+        public async Task Process_AddsHiddenInputTag_FromEndOfFormContent(List<TagBuilder> tagBuilderList, string expectedOutput)
+        {
+            // Arrange
+            var viewContext = new ViewContext();
+            var tagHelperOutput = new TagHelperOutput(
+                tagName: "form",
+                attributes: new TagHelperAttributeList());
+
+            var tagHelperContext = new TagHelperContext(
+                Enumerable.Empty<IReadOnlyTagHelperAttribute>(),
+                new Dictionary<object, object>(),
+                "someId",
+                (useCachedResult) =>
+                {
+                    Assert.True(viewContext.FormContext.CanRenderAtEndOfForm);
+                    foreach (var item in tagBuilderList)
+                    {
+                        viewContext.FormContext.EndOfFormContent.Add(item);
+                    }
+
+                    return Task.FromResult<TagHelperContent>(new DefaultTagHelperContent());
+                });
+
+            var tagHelper = new RenderAtEndOfFormTagHelper
+            {
+                ViewContext = viewContext
+            };
+
+            // Act
+            await tagHelper.ProcessAsync(context: tagHelperContext, output: tagHelperOutput);
+
+            // Assert
+            Assert.Equal(expectedOutput, tagHelperOutput.PostContent.GetContent());
+        }
+
+        private static TagBuilder GetTagBuilder(string tag, string name, string type, string value, TagRenderMode mode)
+        {
+            var tagBuilder = new TagBuilder(tag);
+            tagBuilder.MergeAttribute("name", name);
+            tagBuilder.MergeAttribute("type", type);
+            tagBuilder.MergeAttribute("value", value);
+            tagBuilder.TagRenderMode = mode;
+
+            return tagBuilder;
+        }
+    }
+}

test/Microsoft.AspNet.Mvc.ViewFeatures.Test/Rendering/HtmlHelperCheckboxTest.cs

@@ -5,11 +5,12 @@
 using System;
 using System.Collections.Generic;
 using System.ComponentModel.DataAnnotations;
-using System.Globalization;
+using System.IO;
 using Microsoft.AspNet.Mvc.ModelBinding;
 using Microsoft.AspNet.Mvc.TestCommon;
 using Microsoft.AspNet.Mvc.ViewFeatures;
 using Microsoft.AspNet.Routing;
+using Microsoft.Extensions.WebEncoders.Testing;
 using Xunit;
 
 namespace Microsoft.AspNet.Mvc.Rendering
@@ -127,6 +128,32 @@ namespace Microsoft.AspNet.Mvc.Rendering
             Assert.Equal(expected, HtmlContentUtilities.HtmlContentToString(html));
         }
 
+        [Fact]
+        public void CheckBox_WithCanRenderAtEndOfFormSet_DoesNotGenerateInlineHiddenTag()
+        {
+            // Arrange
+            // Mono issue - https://github.com/aspnet/External/issues/19
+            var expected = PlatformNormalizer.NormalizeContent(
+                @"<input checked=""HtmlEncode[[checked]]"" data-val=""HtmlEncode[[true]]"" " +
+                @"data-val-required=""HtmlEncode[[The Boolean field is required.]]"" id=""HtmlEncode[[Property1]]"" " +
+                @"name=""HtmlEncode[[Property1]]"" type=""HtmlEncode[[checkbox]]"" " +
+                @"value=""HtmlEncode[[true]]"" />");
+            var helper = DefaultTemplatesUtilities.GetHtmlHelper(GetTestModelViewData());
+            helper.ViewContext.FormContext.CanRenderAtEndOfForm = true;
+
+            // Act
+            var html = helper.CheckBox("Property1", isChecked: true, htmlAttributes: null);
+
+            // Assert
+            Assert.True(helper.ViewContext.FormContext.HasEndOfFormContent);
+            Assert.Equal(expected, HtmlContentUtilities.HtmlContentToString(html));
+            var writer = new StringWriter();
+            var hiddenTag = Assert.Single(helper.ViewContext.FormContext.EndOfFormContent);
+            hiddenTag.WriteTo(writer, new CommonTestEncoder());
+            Assert.Equal("<input name=\"HtmlEncode[[Property1]]\" type=\"HtmlEncode[[hidden]]\" value=\"HtmlEncode[[false]]\" />",
+                writer.ToString());
+        }
+
         [Fact]
         public void CheckBoxUsesAttemptedValueFromModelState()
         {

test/Microsoft.AspNet.Mvc.ViewFeatures.Test/Rendering/HtmlHelperFormTest.cs

@@ -2,12 +2,15 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 #if MOCK_SUPPORT
+using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 using Microsoft.AspNet.Http;
 using Microsoft.AspNet.Mvc.Routing;
 using Microsoft.AspNet.Mvc.ViewFeatures;
+using Microsoft.Extensions.WebEncoders;
+using Microsoft.Extensions.WebEncoders.Testing;
 using Moq;
 using Xunit;
 
@@ -318,6 +321,37 @@ namespace Microsoft.AspNet.Mvc.Rendering
             urlHelper.Verify();
         }
 
+        [Fact]
+        public void EndForm_RendersHiddenTagForCheckBox()
+        {
+            // Arrange
+            var htmlHelper = DefaultTemplatesUtilities.GetHtmlHelper();
+            var serviceProvider = new Mock<IServiceProvider>();
+            serviceProvider.Setup(s => s.GetService(typeof(IHtmlEncoder))).Returns(new CommonTestEncoder());
+            var viewContext = htmlHelper.ViewContext;
+            viewContext.HttpContext.RequestServices = serviceProvider.Object;
+
+            var writer = viewContext.Writer as StringWriter;
+            Assert.NotNull(writer);
+            var builder = writer.GetStringBuilder();
+
+            var tagBuilder = new TagBuilder("input");
+            tagBuilder.MergeAttribute("name", "SomeName");
+            tagBuilder.MergeAttribute("type", "hidden");
+            tagBuilder.MergeAttribute("value", "false");
+            tagBuilder.TagRenderMode = TagRenderMode.SelfClosing;
+
+            htmlHelper.ViewContext.FormContext.EndOfFormContent.Add(tagBuilder);
+
+            // Act
+            htmlHelper.EndForm();
+
+            // Assert
+            Assert.Equal(
+                "<input name=\"HtmlEncode[[SomeName]]\" type=\"HtmlEncode[[hidden]]\" value=\"HtmlEncode[[false]]\" /></form>",
+                builder.ToString());
+        }
+
         private string GetHtmlAttributesAsString(object htmlAttributes)
         {
             var dictionary = HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes);

test/WebSites/HtmlGenerationWebSite/Views/HtmlGeneration_Home/Order.cshtml

@@ -11,6 +11,7 @@
 @addTagHelper "Microsoft.AspNet.Mvc.TagHelpers.SelectTagHelper, Microsoft.AspNet.Mvc.TagHelpers"
 @addTagHelper "Microsoft.AspNet.Mvc.TagHelpers.ValidationMessageTagHelper, Microsoft.AspNet.Mvc.TagHelpers"
 @addTagHelper "Microsoft.AspNet.Mvc.TagHelpers.ValidationSummaryTagHelper, Microsoft.AspNet.Mvc.TagHelpers"
+@addTagHelper "Microsoft.AspNet.Mvc.TagHelpers.RenderAtEndOfFormTagHelper, Microsoft.AspNet.Mvc.TagHelpers"
 
 <html>
 <head>