From 6ed589f47d2ff04cf5be13455b96315a2778d00d Mon Sep 17 00:00:00 2001
From: Pranav K <prkrishn@hotmail.com>
Date: Tue, 28 Nov 2017 17:52:22 -0800
Subject: [PATCH] Add a <partial /> tag helper

Fixes #5916
---
 .../PartialTagHelper.cs                       | 113 ++++++
 .../Properties/Resources.Designer.cs          |  14 +
 .../Resources.resx                            |   3 +
 ...ation_Home.ProductListUsingTagHelpers.html |  64 +++
 .../PartialTagHelperTest.cs                   | 382 ++++++++++++++++++
 .../HtmlGeneration_HomeController.cs          |   2 +
 .../ProductListUsingTagHelpers.cshtml         |  30 ++
 7 files changed, 608 insertions(+)
 create mode 100644 src/Microsoft.AspNetCore.Mvc.TagHelpers/PartialTagHelper.cs
 create mode 100644 test/Microsoft.AspNetCore.Mvc.FunctionalTests/compiler/resources/HtmlGenerationWebSite.HtmlGeneration_Home.ProductListUsingTagHelpers.html
 create mode 100644 test/Microsoft.AspNetCore.Mvc.TagHelpers.Test/PartialTagHelperTest.cs
 create mode 100644 test/WebSites/HtmlGenerationWebSite/Views/HtmlGeneration_Home/ProductListUsingTagHelpers.cshtml

diff --git a/src/Microsoft.AspNetCore.Mvc.TagHelpers/PartialTagHelper.cs b/src/Microsoft.AspNetCore.Mvc.TagHelpers/PartialTagHelper.cs
new file mode 100644
index 0000000000..1a04a61ff2
--- /dev/null
+++ b/src/Microsoft.AspNetCore.Mvc.TagHelpers/PartialTagHelper.cs
@@ -0,0 +1,113 @@
+// 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.IO;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Mvc.Rendering;
+using Microsoft.AspNetCore.Mvc.ViewEngines;
+using Microsoft.AspNetCore.Mvc.ViewFeatures;
+using Microsoft.AspNetCore.Mvc.ViewFeatures.Internal;
+using Microsoft.AspNetCore.Razor.TagHelpers;
+
+namespace Microsoft.AspNetCore.Mvc.TagHelpers
+{
+    /// <summary>
+    /// Renders a partial view.
+    /// </summary>
+    [HtmlTargetElement("partial", Attributes = "name", TagStructure = TagStructure.WithoutEndTag)]
+    public class PartialTagHelper : TagHelper
+    {
+        private readonly ICompositeViewEngine _viewEngine;
+        private readonly IViewBufferScope _viewBufferScope;
+
+        public PartialTagHelper(
+            ICompositeViewEngine viewEngine,
+            IViewBufferScope viewBufferScope)
+        {
+            _viewEngine = viewEngine ?? throw new ArgumentNullException(nameof(viewEngine));
+            _viewBufferScope = viewBufferScope ?? throw new ArgumentNullException(nameof(viewBufferScope));
+        }
+
+        /// <summary>
+        /// The name of the partial view used to create the HTML markup.
+        /// </summary>
+        public string Name { get; set; }
+
+        /// <summary>
+        /// A model to pass into the partial view.
+        /// </summary>
+        public object Model { get; set; }
+
+        /// <summary>
+        /// A <see cref="ViewDataDictionary"/> to pass into the partial view.
+        /// </summary>
+        public ViewDataDictionary ViewData { get; set; }
+
+        [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(context));
+            }
+
+            var viewBuffer = new ViewBuffer(_viewBufferScope, Name, ViewBuffer.PartialViewPageSize);
+            using (var writer = new ViewBufferTextWriter(viewBuffer, Encoding.UTF8))
+            {
+                await RenderPartialViewAsync(writer);
+
+                // Reset the TagName. We don't want `partial` to render.
+                output.TagName = null;
+                output.Content.SetHtmlContent(viewBuffer);
+            }
+        }
+
+        private async Task RenderPartialViewAsync(TextWriter writer)
+        {
+            var viewEngineResult = _viewEngine.GetView(ViewContext.ExecutingFilePath, Name, isMainPage: false);
+            var getViewLocations = viewEngineResult.SearchedLocations;
+            if (!viewEngineResult.Success)
+            {
+                viewEngineResult = _viewEngine.FindView(ViewContext, Name, isMainPage: false);
+            }
+
+            if (!viewEngineResult.Success)
+            {
+                var searchedLocations = Enumerable.Concat(getViewLocations, viewEngineResult.SearchedLocations);
+                var locations = string.Empty;
+                if (searchedLocations.Any())
+                {
+                    locations += Environment.NewLine + string.Join(Environment.NewLine, searchedLocations);
+                }
+
+                throw new InvalidOperationException(
+                    Resources.FormatViewEngine_PartialViewNotFound(Name, locations));
+            }
+
+            var view = viewEngineResult.View;
+            using (view as IDisposable)
+            {
+                // Determine which ViewData we should use to construct a new ViewData
+                var baseViewData = ViewData ?? ViewContext.ViewData;
+                var model = Model ?? ViewContext.ViewData.Model;
+
+                var newViewData = new ViewDataDictionary<object>(baseViewData, model);
+                var partialViewContext = new ViewContext(ViewContext, view, newViewData, writer);
+
+                await view.RenderAsync(partialViewContext);
+            }
+        }
+    }
+}
diff --git a/src/Microsoft.AspNetCore.Mvc.TagHelpers/Properties/Resources.Designer.cs b/src/Microsoft.AspNetCore.Mvc.TagHelpers/Properties/Resources.Designer.cs
index 411940c2a9..c590669745 100644
--- a/src/Microsoft.AspNetCore.Mvc.TagHelpers/Properties/Resources.Designer.cs
+++ b/src/Microsoft.AspNetCore.Mvc.TagHelpers/Properties/Resources.Designer.cs
@@ -178,6 +178,20 @@ internal static string ArgumentCannotContainHtmlSpace
         internal static string FormatArgumentCannotContainHtmlSpace()
             => GetString("ArgumentCannotContainHtmlSpace");
 
+        /// <summary>
+        /// The partial view '{0}' was not found. The following locations were searched:{1}
+        /// </summary>
+        internal static string ViewEngine_PartialViewNotFound
+        {
+            get => GetString("ViewEngine_PartialViewNotFound");
+        }
+
+        /// <summary>
+        /// The partial view '{0}' was not found. The following locations were searched:{1}
+        /// </summary>
+        internal static string FormatViewEngine_PartialViewNotFound(object p0, object p1)
+            => string.Format(CultureInfo.CurrentCulture, GetString("ViewEngine_PartialViewNotFound"), p0, p1);
+
         private static string GetString(string name, params string[] formatterNames)
         {
             var value = _resourceManager.GetString(name);
diff --git a/src/Microsoft.AspNetCore.Mvc.TagHelpers/Resources.resx b/src/Microsoft.AspNetCore.Mvc.TagHelpers/Resources.resx
index 7242ee001b..e93c480395 100644
--- a/src/Microsoft.AspNetCore.Mvc.TagHelpers/Resources.resx
+++ b/src/Microsoft.AspNetCore.Mvc.TagHelpers/Resources.resx
@@ -153,4 +153,7 @@
   <data name="ArgumentCannotContainHtmlSpace" xml:space="preserve">
     <value>Value cannot contain HTML space characters.</value>
   </data>
+  <data name="ViewEngine_PartialViewNotFound" xml:space="preserve">
+    <value>The partial view '{0}' was not found. The following locations were searched:{1}</value>
+  </data>
 </root>
\ No newline at end of file
diff --git a/test/Microsoft.AspNetCore.Mvc.FunctionalTests/compiler/resources/HtmlGenerationWebSite.HtmlGeneration_Home.ProductListUsingTagHelpers.html b/test/Microsoft.AspNetCore.Mvc.FunctionalTests/compiler/resources/HtmlGenerationWebSite.HtmlGeneration_Home.ProductListUsingTagHelpers.html
new file mode 100644
index 0000000000..afa2cc3bc6
--- /dev/null
+++ b/test/Microsoft.AspNetCore.Mvc.FunctionalTests/compiler/resources/HtmlGenerationWebSite.HtmlGeneration_Home.ProductListUsingTagHelpers.html
@@ -0,0 +1,64 @@
+<html>
+<head>
+    <meta charset="utf-8" />
+</head>
+<body>
+    <form action="/HtmlGeneration_Product" method="post">
+            <div>
+                <label class="product" for="z0__product_HomePage">HomePage</label>
+                <input type="url" size="50" disabled="disabled" readonly="readonly" id="z0__product_HomePage" name="[0].product.HomePage" value="http://www.contoso.com/" />
+            </div>
+            
+<div>
+    <label class="product" for="z0__Number">Number</label>
+    <input type="number" data-val="true" data-val-required="The Number field is required." id="z0__Number" name="[0].Number" value="0" />
+</div>
+<div>
+    <label class="product" for="z0__ProductName">ProductName</label>
+    <input type="text" data-val="true" data-val-required="The ProductName field is required." id="z0__ProductName" name="[0].ProductName" value="Product_0" />
+</div>
+<div>
+    <label class="product" for="z0__Description">Description</label>
+    <textarea rows="4" cols="50" class="product" id="z0__Description" name="[0].Description">
+</textarea>
+</div>
+            <div>
+                <label class="product" for="z1__product_HomePage">HomePage</label>
+                <input type="url" size="50" disabled="disabled" readonly="readonly" id="z1__product_HomePage" name="[1].product.HomePage" value="" />
+            </div>
+            
+<div>
+    <label class="product" for="z1__Number">Number</label>
+    <input type="number" data-val="true" data-val-required="The Number field is required." id="z1__Number" name="[1].Number" value="1" />
+</div>
+<div>
+    <label class="product" for="z1__ProductName">ProductName</label>
+    <input type="text" data-val="true" data-val-required="The ProductName field is required." id="z1__ProductName" name="[1].ProductName" value="Product_1" />
+</div>
+<div>
+    <label class="product" for="z1__Description">Description</label>
+    <textarea rows="4" cols="50" class="product" id="z1__Description" name="[1].Description">
+</textarea>
+</div>
+            <div>
+                <label class="product" for="z2__product_HomePage">HomePage</label>
+                <input type="url" size="50" disabled="disabled" readonly="readonly" id="z2__product_HomePage" name="[2].product.HomePage" value="" />
+            </div>
+            
+<div>
+    <label class="product" for="z2__Number">Number</label>
+    <input type="number" data-val="true" data-val-required="The Number field is required." id="z2__Number" name="[2].Number" value="2" />
+</div>
+<div>
+    <label class="product" for="z2__ProductName">ProductName</label>
+    <input type="text" data-val="true" data-val-required="The ProductName field is required." id="z2__ProductName" name="[2].ProductName" value="Product_2" />
+</div>
+<div>
+    <label class="product" for="z2__Description">Description</label>
+    <textarea rows="4" cols="50" class="product" id="z2__Description" name="[2].Description">
+Product_2 description</textarea>
+</div>
+        <input type="submit" />
+    <input name="__RequestVerificationToken" type="hidden" value="{0}" /></form>
+</body>
+</html>
diff --git a/test/Microsoft.AspNetCore.Mvc.TagHelpers.Test/PartialTagHelperTest.cs b/test/Microsoft.AspNetCore.Mvc.TagHelpers.Test/PartialTagHelperTest.cs
new file mode 100644
index 0000000000..54c58cc8aa
--- /dev/null
+++ b/test/Microsoft.AspNetCore.Mvc.TagHelpers.Test/PartialTagHelperTest.cs
@@ -0,0 +1,382 @@
+// 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.Collections.Generic;
+using System.IO;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Mvc.Abstractions;
+using Microsoft.AspNetCore.Mvc.ModelBinding;
+using Microsoft.AspNetCore.Mvc.Rendering;
+using Microsoft.AspNetCore.Mvc.TestCommon;
+using Microsoft.AspNetCore.Mvc.ViewEngines;
+using Microsoft.AspNetCore.Mvc.ViewFeatures;
+using Microsoft.AspNetCore.Mvc.ViewFeatures.Internal;
+using Microsoft.AspNetCore.Razor.TagHelpers;
+using Microsoft.AspNetCore.Routing;
+using Microsoft.Extensions.WebEncoders.Testing;
+using Moq;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Mvc.TagHelpers
+{
+    public class PartialTagHelperTest
+    {
+        [Fact]
+        public async Task ProcessAsync_RendersPartialView_IfGetViewReturnsView()
+        {
+            // Arrange
+            var expected = "Hello world!";
+            var bufferScope = new TestViewBufferScope();
+            var partialName = "_Partial";
+            var model = new object();
+            var viewContext = GetViewContext();
+
+            var view = new Mock<IView>();
+            view.Setup(v => v.RenderAsync(It.IsAny<ViewContext>()))
+                .Callback((ViewContext v) =>
+                {
+                    v.Writer.Write(expected);
+                })
+                .Returns(Task.CompletedTask);
+
+            var viewEngine = new Mock<ICompositeViewEngine>();
+            viewEngine.Setup(v => v.GetView(It.IsAny<string>(), partialName, false))
+                .Returns(ViewEngineResult.Found(partialName, view.Object));
+
+            var tagHelper = new PartialTagHelper(viewEngine.Object, bufferScope)
+            {
+                Name = partialName,
+                Model = model,
+                ViewContext = viewContext,
+            };
+            var tagHelperContext = GetTagHelperContext();
+            var output = GetTagHelperOutput();
+
+            // Act
+            await tagHelper.ProcessAsync(tagHelperContext, output);
+
+            // Assert
+            var content = HtmlContentUtilities.HtmlContentToString(output.Content, new HtmlTestEncoder());
+            Assert.Equal(expected, content);
+        }
+
+        [Fact]
+        public async Task ProcessAsync_RendersPartialView_IfFindViewReturnsView()
+        {
+            // Arrange
+            var expected = "Hello world!";
+            var bufferScope = new TestViewBufferScope();
+            var partialName = "_Partial";
+            var model = new object();
+            var viewContext = GetViewContext();
+
+            var view = new Mock<IView>();
+            view.Setup(v => v.RenderAsync(It.IsAny<ViewContext>()))
+                .Callback((ViewContext v) =>
+                {
+                    v.Writer.Write(expected);
+                })
+                .Returns(Task.CompletedTask);
+
+            var viewEngine = new Mock<ICompositeViewEngine>();
+            viewEngine.Setup(v => v.GetView(It.IsAny<string>(), partialName, false))
+                .Returns(ViewEngineResult.NotFound(partialName, new[] { partialName }));
+
+            viewEngine.Setup(v => v.FindView(viewContext, partialName, false))
+                .Returns(ViewEngineResult.Found(partialName, view.Object));
+
+            var tagHelper = new PartialTagHelper(viewEngine.Object, bufferScope)
+            {
+                Name = partialName,
+                Model = model,
+                ViewContext = viewContext,
+            };
+            var tagHelperContext = GetTagHelperContext();
+            var output = GetTagHelperOutput();
+
+            // Act
+            await tagHelper.ProcessAsync(tagHelperContext, output);
+
+            // Assert
+            var content = HtmlContentUtilities.HtmlContentToString(output.Content, new HtmlTestEncoder());
+            Assert.Equal(expected, content);
+        }
+
+        [Fact]
+        public async Task ProcessAsync_UsesViewDataFromContext()
+        {
+            // Arrange
+            var expected = "Hello world!";
+            var bufferScope = new TestViewBufferScope();
+            var partialName = "_Partial";
+            var model = new object();
+            var viewContext = GetViewContext();
+            viewContext.ViewData["key"] = expected;
+
+            var view = new Mock<IView>();
+            view.Setup(v => v.RenderAsync(It.IsAny<ViewContext>()))
+                .Callback((ViewContext v) =>
+                {
+                    v.Writer.Write(v.ViewData["key"]);
+                })
+                .Returns(Task.CompletedTask);
+
+            var viewEngine = new Mock<ICompositeViewEngine>();
+            viewEngine.Setup(v => v.GetView(It.IsAny<string>(), partialName, false))
+                .Returns(ViewEngineResult.NotFound(partialName, new[] { partialName }));
+
+            viewEngine.Setup(v => v.FindView(viewContext, partialName, false))
+                .Returns(ViewEngineResult.Found(partialName, view.Object));
+
+            var tagHelper = new PartialTagHelper(viewEngine.Object, bufferScope)
+            {
+                Name = partialName,
+                Model = model,
+                ViewContext = viewContext,
+            };
+            var tagHelperContext = GetTagHelperContext();
+            var output = GetTagHelperOutput();
+
+            // Act
+            await tagHelper.ProcessAsync(tagHelperContext, output);
+
+            // Assert
+            var content = HtmlContentUtilities.HtmlContentToString(output.Content, new HtmlTestEncoder());
+            Assert.Equal(expected, content);
+        }
+
+        [Fact]
+        public async Task ProcessAsync_UsesPassedInViewData_WhenNotNull()
+        {
+            // Arrange
+            var expected = "Hello world!";
+            var bufferScope = new TestViewBufferScope();
+            var partialName = "_Partial";
+            var model = new object();
+            var viewData = new ViewDataDictionary(new TestModelMetadataProvider(), new ModelStateDictionary());
+            viewData["key"] = expected;
+            var viewContext = GetViewContext();
+            viewContext.ViewData["key"] = "ViewContext";
+
+
+            var view = new Mock<IView>();
+            view.Setup(v => v.RenderAsync(It.IsAny<ViewContext>()))
+                .Callback((ViewContext v) =>
+                {
+                    v.Writer.Write(v.ViewData["key"]);
+                })
+                .Returns(Task.CompletedTask);
+
+            var viewEngine = new Mock<ICompositeViewEngine>();
+            viewEngine.Setup(v => v.GetView(It.IsAny<string>(), partialName, false))
+                .Returns(ViewEngineResult.Found(partialName, view.Object));
+
+            var tagHelper = new PartialTagHelper(viewEngine.Object, bufferScope)
+            {
+                Name = partialName,
+                Model = model,
+                ViewContext = viewContext,
+                ViewData = viewData,
+            };
+            var tagHelperContext = GetTagHelperContext();
+            var output = GetTagHelperOutput();
+
+            // Act
+            await tagHelper.ProcessAsync(tagHelperContext, output);
+
+            // Assert
+            var content = HtmlContentUtilities.HtmlContentToString(output.Content, new HtmlTestEncoder());
+            Assert.Equal(expected, content);
+        }
+
+        [Fact]
+        public async Task ProcessAsync_UsesPassedInModel()
+        {
+            // Arrange
+            var expected = "Hello world!";
+            var bufferScope = new TestViewBufferScope();
+            var partialName = "_Partial";
+            var model = new object();
+            var viewContext = GetViewContext();
+            viewContext.ViewData.Model = new object();
+
+            var view = new Mock<IView>();
+            view.Setup(v => v.RenderAsync(It.IsAny<ViewContext>()))
+                .Callback((ViewContext v) =>
+                {
+                    Assert.Same(model, v.ViewData.Model);
+                    v.Writer.Write(expected);
+                })
+                .Returns(Task.CompletedTask);
+
+            var viewEngine = new Mock<ICompositeViewEngine>();
+            viewEngine.Setup(v => v.GetView(It.IsAny<string>(), partialName, false))
+                .Returns(ViewEngineResult.Found(partialName, view.Object));
+
+            var tagHelper = new PartialTagHelper(viewEngine.Object, bufferScope)
+            {
+                Name = partialName,
+                ViewContext = viewContext,
+                Model = model,
+            };
+            var tagHelperContext = GetTagHelperContext();
+            var output = GetTagHelperOutput();
+
+            // Act
+            await tagHelper.ProcessAsync(tagHelperContext, output);
+
+            // Assert
+            var content = HtmlContentUtilities.HtmlContentToString(output.Content, new HtmlTestEncoder());
+            Assert.Equal(expected, content);
+        }
+
+        [Fact]
+        public async Task ProcessAsync_UsesModelOnViewContextViewData_WhenModelPropertyIsNull()
+        {
+            // Arrange
+            var expected = "Hello world!";
+            var bufferScope = new TestViewBufferScope();
+            var partialName = "_Partial";
+            var model = new object();
+            var viewContext = GetViewContext();
+            viewContext.ViewData.Model = model;
+
+            var view = new Mock<IView>();
+            view.Setup(v => v.RenderAsync(It.IsAny<ViewContext>()))
+                .Callback((ViewContext v) =>
+                {
+                    Assert.Same(model, v.ViewData.Model);
+                    v.Writer.Write(expected);
+                })
+                .Returns(Task.CompletedTask);
+
+            var viewEngine = new Mock<ICompositeViewEngine>();
+            viewEngine.Setup(v => v.GetView(It.IsAny<string>(), partialName, false))
+                .Returns(ViewEngineResult.Found(partialName, view.Object));
+
+            var tagHelper = new PartialTagHelper(viewEngine.Object, bufferScope)
+            {
+                Name = partialName,
+                ViewContext = viewContext,
+            };
+            var tagHelperContext = GetTagHelperContext();
+            var output = GetTagHelperOutput();
+
+            // Act
+            await tagHelper.ProcessAsync(tagHelperContext, output);
+
+            // Assert
+            var content = HtmlContentUtilities.HtmlContentToString(output.Content, new HtmlTestEncoder());
+            Assert.Equal(expected, content);
+        }
+
+        [Fact]
+        public async Task ProcessAsync_DisposesViewInstance()
+        {
+            // Arrange
+            var expected = "Hello world!";
+            var bufferScope = new TestViewBufferScope();
+            var partialName = "_Partial";
+            var model = new object();
+            var viewContext = GetViewContext();
+
+            var disposable = new Mock<IDisposable>();
+            disposable.Setup(d => d.Dispose()).Verifiable();
+            var view = disposable.As<IView>();
+
+            view.Setup(v => v.RenderAsync(It.IsAny<ViewContext>()))
+                .Callback((ViewContext v) =>
+                {
+                    v.Writer.Write(expected);
+                })
+                .Returns(Task.CompletedTask);
+
+            var viewEngine = new Mock<ICompositeViewEngine>();
+            viewEngine.Setup(v => v.GetView(It.IsAny<string>(), partialName, false))
+                .Returns(ViewEngineResult.Found(partialName, view.Object));
+
+            var tagHelper = new PartialTagHelper(viewEngine.Object, bufferScope)
+            {
+                Name = partialName,
+                Model = model,
+                ViewContext = viewContext,
+            };
+            var tagHelperContext = GetTagHelperContext();
+            var output = GetTagHelperOutput();
+
+            // Act
+            await tagHelper.ProcessAsync(tagHelperContext, output);
+
+            // Assert
+            disposable.Verify();
+        }
+
+        [Fact]
+        public async Task ProcessAsync_Throws_IfGetViewAndFindReturnNotFoundResults()
+        {
+            // Arrange
+            var bufferScope = new TestViewBufferScope();
+            var partialName = "_Partial";
+            var expected = string.Join(Environment.NewLine,
+                $"The partial view '{partialName}' was not found. The following locations were searched:",
+                "NotFound1",
+                "NotFound2",
+                "NotFound3",
+                "NotFound4");
+            var viewData = new ViewDataDictionary(new TestModelMetadataProvider(), new ModelStateDictionary());
+            var viewContext = GetViewContext();
+
+            var view = Mock.Of<IView>();
+            var viewEngine = new Mock<ICompositeViewEngine>();
+            viewEngine.Setup(v => v.GetView(It.IsAny<string>(), partialName, false))
+                .Returns(ViewEngineResult.NotFound(partialName, new[] { "NotFound1", "NotFound2" }));
+
+            viewEngine.Setup(v => v.FindView(viewContext, partialName, false))
+                .Returns(ViewEngineResult.NotFound(partialName, new[] { $"NotFound3", $"NotFound4" }));
+
+            var tagHelper = new PartialTagHelper(viewEngine.Object, bufferScope)
+            {
+                Name = partialName,
+                ViewContext = viewContext,
+                ViewData = viewData,
+            };
+            var tagHelperContext = GetTagHelperContext();
+            var output = GetTagHelperOutput();
+
+            // Act & Assert
+            var exception = await Assert.ThrowsAsync<InvalidOperationException>(
+                () => tagHelper.ProcessAsync(tagHelperContext, output));
+            Assert.Equal(expected, exception.Message);
+        }
+
+        private static ViewContext GetViewContext()
+        {
+            return new ViewContext(
+                new ActionContext(new DefaultHttpContext(), new RouteData(), new ActionDescriptor()),
+                NullView.Instance,
+                new ViewDataDictionary(new TestModelMetadataProvider(), new ModelStateDictionary()),
+                Mock.Of<ITempDataDictionary>(),
+                TextWriter.Null,
+                new HtmlHelperOptions());
+        }
+
+        private static TagHelperContext GetTagHelperContext()
+        {
+            return new TagHelperContext(
+                "partial",
+                new TagHelperAttributeList(),
+                new Dictionary<object, object>(),
+                Guid.NewGuid().ToString("N"));
+        }
+
+        private static TagHelperOutput GetTagHelperOutput()
+        {
+            return new TagHelperOutput(
+                "partial",
+                new TagHelperAttributeList(),
+                (_, __) => Task.FromResult<TagHelperContent>(new DefaultTagHelperContent()));
+        }
+    }
+}
diff --git a/test/WebSites/HtmlGenerationWebSite/Controllers/HtmlGeneration_HomeController.cs b/test/WebSites/HtmlGenerationWebSite/Controllers/HtmlGeneration_HomeController.cs
index 3736f9554c..3402b1fbdf 100644
--- a/test/WebSites/HtmlGenerationWebSite/Controllers/HtmlGeneration_HomeController.cs
+++ b/test/WebSites/HtmlGenerationWebSite/Controllers/HtmlGeneration_HomeController.cs
@@ -108,6 +108,8 @@ public IActionResult ProductList()
             return View(_products);
         }
 
+        public IActionResult ProductListUsingTagHelpers() => View(_products);
+
         public IActionResult EmployeeList()
         {
             var employees = new List<Employee>
diff --git a/test/WebSites/HtmlGenerationWebSite/Views/HtmlGeneration_Home/ProductListUsingTagHelpers.cshtml b/test/WebSites/HtmlGenerationWebSite/Views/HtmlGeneration_Home/ProductListUsingTagHelpers.cshtml
new file mode 100644
index 0000000000..218277c8e4
--- /dev/null
+++ b/test/WebSites/HtmlGenerationWebSite/Views/HtmlGeneration_Home/ProductListUsingTagHelpers.cshtml
@@ -0,0 +1,30 @@
+@using HtmlGenerationWebSite.Models
+@model IEnumerable<Product>
+
+@addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers
+
+<html>
+<head>
+    <meta charset="utf-8" />
+</head>
+<body>
+    <form asp-action="Index" asp-controller="HtmlGeneration_Product" asp-antiforgery="true">
+    @{
+        var index = 0;
+        var fieldPrefix = ViewData.TemplateInfo.HtmlFieldPrefix;
+        foreach (var product in Model)
+        {
+            @* Update HtmlFieldPrefix so generated for, id and name attribute values are correct. *@
+            ViewData.TemplateInfo.HtmlFieldPrefix = fieldPrefix + string.Format("[{0}]", index++);
+            <div>
+                <label asp-for="@product.HomePage" class="product"></label>
+                <input asp-for="@product.HomePage" type="url" size="50" disabled="disabled" readonly="readonly" />
+            </div>
+            <partial name="_ProductPartial" model="@product" />
+            ViewData.TemplateInfo.HtmlFieldPrefix = fieldPrefix;
+        }
+        <input type="submit" />
+    }
+    </form>
+</body>
+</html>