[Fixes #4013] Added support for areas in 'a' and 'form' tag helpers

src/Microsoft.AspNetCore.Mvc.TagHelpers/AnchorTagHelper.cs

@@ -14,6 +14,7 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
     /// </summary>
     [HtmlTargetElement("a", Attributes = ActionAttributeName)]
     [HtmlTargetElement("a", Attributes = ControllerAttributeName)]
+    [HtmlTargetElement("a", Attributes = AreaAttributeName)]
     [HtmlTargetElement("a", Attributes = FragmentAttributeName)]
     [HtmlTargetElement("a", Attributes = HostAttributeName)]
     [HtmlTargetElement("a", Attributes = ProtocolAttributeName)]
@@ -24,6 +25,7 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
     {
         private const string ActionAttributeName = "asp-action";
         private const string ControllerAttributeName = "asp-controller";
+        private const string AreaAttributeName = "asp-area";
         private const string FragmentAttributeName = "asp-fragment";
         private const string HostAttributeName = "asp-host";
         private const string ProtocolAttributeName = "asp-protocol";
@@ -67,6 +69,13 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
         [HtmlAttributeName(ControllerAttributeName)]
         public string Controller { get; set; }
 
+        /// <summary>
+        /// The name of the area.
+        /// </summary>
+        /// <remarks>Must be <c>null</c> if <see cref="Route"/> is non-<c>null</c>.</remarks>
+        [HtmlAttributeName(AreaAttributeName)]
+        public string Area { get; set; }
+
         /// <summary>
         /// The protocol for the URL, such as &quot;http&quot; or &quot;https&quot;.
         /// </summary>
@@ -147,6 +156,7 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
             {
                 if (Action != null ||
                     Controller != null ||
+                    Area != null ||
                     Route != null ||
                     Protocol != null ||
                     Host != null ||
@@ -159,6 +169,7 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
                             "<a>",
                             ActionAttributeName,
                             ControllerAttributeName,
+                            AreaAttributeName,
                             RouteAttributeName,
                             ProtocolAttributeName,
                             HostAttributeName,
@@ -180,6 +191,17 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
                     }
                 }
 
+                if (Area != null)
+                {
+                    if (routeValues == null)
+                    {
+                        routeValues = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase);
+                    }
+
+                    // Unconditionally replace any value from asp-route-area. 
+                    routeValues["area"] = Area;
+                }
+
                 TagBuilder tagBuilder;
                 if (Route == null)
                 {

src/Microsoft.AspNetCore.Mvc.TagHelpers/FormTagHelper.cs

@@ -15,6 +15,7 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
     /// </summary>
     [HtmlTargetElement("form", Attributes = ActionAttributeName)]
     [HtmlTargetElement("form", Attributes = AntiforgeryAttributeName)]
+    [HtmlTargetElement("form", Attributes = AreaAttributeName)]
     [HtmlTargetElement("form", Attributes = ControllerAttributeName)]
     [HtmlTargetElement("form", Attributes = RouteAttributeName)]
     [HtmlTargetElement("form", Attributes = RouteValuesDictionaryName)]
@@ -23,6 +24,7 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
     {
         private const string ActionAttributeName = "asp-action";
         private const string AntiforgeryAttributeName = "asp-antiforgery";
+        private const string AreaAttributeName = "asp-area";
         private const string ControllerAttributeName = "asp-controller";
         private const string RouteAttributeName = "asp-route";
         private const string RouteValuesDictionaryName = "asp-all-route-data";
@@ -66,6 +68,12 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
         [HtmlAttributeName(ControllerAttributeName)]
         public string Controller { get; set; }
 
+        /// <summary>
+        /// The name of the area.
+        /// </summary>
+        [HtmlAttributeName(AreaAttributeName)]
+        public string Area { get; set; }
+
         /// <summary>
         /// Whether the antiforgery token should be generated.
         /// </summary>
@@ -141,7 +149,7 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
             // If "action" is already set, it means the user is attempting to use a normal <form>.
             if (output.Attributes.ContainsName(HtmlActionAttributeName))
             {
-                if (Action != null || Controller != null || Route != null || RouteValues.Count != 0)
+                if (Action != null || Controller != null || Area != null || Route != null || RouteValues.Count != 0)
                 {
                     // User also specified bound attributes we cannot use.
                     throw new InvalidOperationException(
@@ -150,6 +158,7 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
                             HtmlActionAttributeName,
                             ActionAttributeName,
                             ControllerAttributeName,
+                            AreaAttributeName,
                             RouteAttributeName,
                             RouteValuesPrefix));
                 }
@@ -171,6 +180,17 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
                     }
                 }
 
+                if (Area != null)
+                {
+                    if (routeValues == null)
+                    {
+                        routeValues = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase);
+                    }
+
+                    // Unconditionally replace any value from asp-route-area. 
+                    routeValues["area"] = Area;
+                }
+
                 TagBuilder tagBuilder;
                 if (Route == null)
                 {

src/Microsoft.AspNetCore.Mvc.TagHelpers/Properties/Resources.Designer.cs

@@ -27,7 +27,7 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
         }
 
         /// <summary>
-        /// Cannot override the '{8}' attribute for {0}. An {0} with a specified '{8}' must not have attributes starting with '{7}' or an '{1}', '{2}', '{3}', '{4}', '{5}', or '{6}' attribute.
+        /// Cannot override the '{9}' attribute for {0}. An {0} with a specified '{9}' must not have attributes starting with '{8}' or an '{1}', '{2}', '{3}', '{4}', '{5}', '{6}', or '{7}' attribute.
         /// </summary>
         internal static string AnchorTagHelper_CannotOverrideHref
         {
@@ -35,15 +35,15 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
         }
 
         /// <summary>
-        /// Cannot override the '{8}' attribute for {0}. An {0} with a specified '{8}' must not have attributes starting with '{7}' or an '{1}', '{2}', '{3}', '{4}', '{5}', or '{6}' attribute.
+        /// Cannot override the '{9}' attribute for {0}. An {0} with a specified '{9}' must not have attributes starting with '{8}' or an '{1}', '{2}', '{3}', '{4}', '{5}', '{6}', or '{7}' attribute.
         /// </summary>
-        internal static string FormatAnchorTagHelper_CannotOverrideHref(object p0, object p1, object p2, object p3, object p4, object p5, object p6, object p7, object p8)
+        internal static string FormatAnchorTagHelper_CannotOverrideHref(object p0, object p1, object p2, object p3, object p4, object p5, object p6, object p7, object p8, object p9)
         {
-            return string.Format(CultureInfo.CurrentCulture, GetString("AnchorTagHelper_CannotOverrideHref"), p0, p1, p2, p3, p4, p5, p6, p7, p8);
+            return string.Format(CultureInfo.CurrentCulture, GetString("AnchorTagHelper_CannotOverrideHref"), p0, p1, p2, p3, p4, p5, p6, p7, p8, p9);
         }
 
         /// <summary>
-        /// Cannot override the '{1}' attribute for {0}. A {0} with a specified '{1}' must not have attributes starting with '{5}' or an '{2}' or '{3}' or '{4}' attribute.
+        /// Cannot override the '{1}' attribute for {0}. A {0} with a specified '{1}' must not have attributes starting with '{6}' or an '{2}' or '{3}' or '{4}' or '{5}' attribute.
         /// </summary>
         internal static string FormTagHelper_CannotOverrideAction
         {
@@ -51,11 +51,11 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
         }
 
         /// <summary>
-        /// Cannot override the '{1}' attribute for {0}. A {0} with a specified '{1}' must not have attributes starting with '{5}' or an '{2}' or '{3}' or '{4}' attribute.
+        /// Cannot override the '{1}' attribute for {0}. A {0} with a specified '{1}' must not have attributes starting with '{6}' or an '{2}' or '{3}' or '{4}' or '{5}' attribute.
         /// </summary>
-        internal static string FormatFormTagHelper_CannotOverrideAction(object p0, object p1, object p2, object p3, object p4, object p5)
+        internal static string FormatFormTagHelper_CannotOverrideAction(object p0, object p1, object p2, object p3, object p4, object p5, object p6)
         {
-            return string.Format(CultureInfo.CurrentCulture, GetString("FormTagHelper_CannotOverrideAction"), p0, p1, p2, p3, p4, p5);
+            return string.Format(CultureInfo.CurrentCulture, GetString("FormTagHelper_CannotOverrideAction"), p0, p1, p2, p3, p4, p5, p6);
         }
 
         /// <summary>

src/Microsoft.AspNetCore.Mvc.TagHelpers/Resources.resx

@@ -121,10 +121,10 @@
     <value>Cannot determine an '{4}' attribute for {0}. An {0} with a specified '{1}' must not have an '{2}' or '{3}' attribute.</value>
   </data>
   <data name="AnchorTagHelper_CannotOverrideHref" xml:space="preserve">
-    <value>Cannot override the '{8}' attribute for {0}. An {0} with a specified '{8}' must not have attributes starting with '{7}' or an '{1}', '{2}', '{3}', '{4}', '{5}', or '{6}' attribute.</value>
+    <value>Cannot override the '{9}' attribute for {0}. An {0} with a specified '{9}' must not have attributes starting with '{8}' or an '{1}', '{2}', '{3}', '{4}', '{5}', '{6}', or '{7}' attribute.</value>
   </data>
   <data name="FormTagHelper_CannotOverrideAction" xml:space="preserve">
-    <value>Cannot override the '{1}' attribute for {0}. A {0} with a specified '{1}' must not have attributes starting with '{5}' or an '{2}' or '{3}' or '{4}' attribute.</value>
+    <value>Cannot override the '{1}' attribute for {0}. A {0} with a specified '{1}' must not have attributes starting with '{6}' or an '{2}' or '{3}' or '{4}' or '{5}' attribute.</value>
   </data>
   <data name="InputTagHelper_InvalidExpressionResult" xml:space="preserve">
     <value>Unexpected '{1}' expression result type '{2}' for {0}. '{1}' must be of type '{3}' if '{4}' is '{5}'.</value>

test/Microsoft.AspNetCore.Mvc.TagHelpers.Test/AnchorTagHelperTest.cs

@@ -187,6 +187,178 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
             Assert.True(output.Content.IsEmpty);
         }
 
+        [Fact]
+        public async Task ProcessAsync_AddsAreaToRouteValuesAndCallsIntoActionLinkWithExpectedParameters()
+        {
+            // Arrange
+            var context = new TagHelperContext(
+                allAttributes: new TagHelperAttributeList(
+                    Enumerable.Empty<TagHelperAttribute>()),
+                items: new Dictionary<object, object>(),
+                uniqueId: "test");
+            var output = new TagHelperOutput(
+                "a",
+                attributes: new TagHelperAttributeList(),
+                getChildContentAsync: (useCachedResult, encoder) =>
+                {
+                    var tagHelperContent = new DefaultTagHelperContent();
+                    tagHelperContent.SetContent("Something");
+                    return Task.FromResult<TagHelperContent>(tagHelperContent);
+                });
+            output.Content.SetContent(string.Empty);
+
+            var generator = new Mock<IHtmlGenerator>();
+            var expectedRouteValues = new Dictionary<string, object> { { "area", "Admin" } };
+
+            generator
+                .Setup(mock => mock.GenerateActionLink(
+                    It.IsAny<ViewContext>(),
+                    string.Empty,
+                    "Index",
+                    "Home",
+                    "http",
+                    "contoso.com",
+                    "hello=world",
+                    expectedRouteValues,
+                    null))
+                .Returns(new TagBuilder("a"))
+                .Verifiable();
+            var anchorTagHelper = new AnchorTagHelper(generator.Object)
+            {
+                Action = "Index",
+                Controller = "Home",
+                Area = "Admin",
+                Fragment = "hello=world",
+                Host = "contoso.com",
+                Protocol = "http",
+            };
+
+            // Act
+            await anchorTagHelper.ProcessAsync(context, output);
+
+            // Assert
+            generator.Verify();
+
+            Assert.Equal("a", output.TagName);
+            Assert.Empty(output.Attributes);
+            Assert.True(output.Content.IsEmpty);
+        }
+
+        [Fact]
+        public async Task ProcessAsync_AspAreaOverridesAspRouteArea()
+        {
+            // Arrange
+            var context = new TagHelperContext(
+                allAttributes: new TagHelperAttributeList(
+                    Enumerable.Empty<TagHelperAttribute>()),
+                items: new Dictionary<object, object>(),
+                uniqueId: "test");
+            var output = new TagHelperOutput(
+                "a",
+                attributes: new TagHelperAttributeList(),
+                getChildContentAsync: (useCachedResult, encoder) =>
+                {
+                    var tagHelperContent = new DefaultTagHelperContent();
+                    tagHelperContent.SetContent("Something");
+                    return Task.FromResult<TagHelperContent>(tagHelperContent);
+                });
+            output.Content.SetContent(string.Empty);
+
+            var generator = new Mock<IHtmlGenerator>();
+            var expectedRouteValues = new Dictionary<string, object> { { "area", "Admin" } };
+
+            generator
+                .Setup(mock => mock.GenerateActionLink(
+                    It.IsAny<ViewContext>(),
+                    string.Empty,
+                    "Index",
+                    "Home",
+                    "http",
+                    "contoso.com",
+                    "hello=world",
+                    expectedRouteValues,
+                    null))
+                .Returns(new TagBuilder("a"))
+                .Verifiable();
+            var anchorTagHelper = new AnchorTagHelper(generator.Object)
+            {
+                Action = "Index",
+                Controller = "Home",
+                Area = "Admin",
+                Fragment = "hello=world",
+                Host = "contoso.com",
+                Protocol = "http",
+                RouteValues = new Dictionary<string, string> { { "area", "Home" } }
+            };
+
+            // Act
+            await anchorTagHelper.ProcessAsync(context, output);
+
+            // Assert
+            generator.Verify();
+
+            Assert.Equal("a", output.TagName);
+            Assert.Empty(output.Attributes);
+            Assert.True(output.Content.IsEmpty);
+        }
+
+        [Fact]
+        public async Task ProcessAsync_EmptyStringOnAspAreaIsPassedThroughToRouteValues()
+        {
+            // Arrange
+            var context = new TagHelperContext(
+                allAttributes: new TagHelperAttributeList(
+                    Enumerable.Empty<TagHelperAttribute>()),
+                items: new Dictionary<object, object>(),
+                uniqueId: "test");
+            var output = new TagHelperOutput(
+                "a",
+                attributes: new TagHelperAttributeList(),
+                getChildContentAsync: (useCachedResult, encoder) =>
+                {
+                    var tagHelperContent = new DefaultTagHelperContent();
+                    tagHelperContent.SetContent("Something");
+                    return Task.FromResult<TagHelperContent>(tagHelperContent);
+                });
+            output.Content.SetContent(string.Empty);
+
+            var generator = new Mock<IHtmlGenerator>();
+            var expectedRouteValues = new Dictionary<string, object> { { "area", string.Empty } };
+
+            generator
+                .Setup(mock => mock.GenerateActionLink(
+                    It.IsAny<ViewContext>(),
+                    string.Empty,
+                    "Index",
+                    "Home",
+                    "http",
+                    "contoso.com",
+                    "hello=world",
+                    expectedRouteValues,
+                    null))
+                .Returns(new TagBuilder("a"))
+                .Verifiable();
+            var anchorTagHelper = new AnchorTagHelper(generator.Object)
+            {
+                Action = "Index",
+                Controller = "Home",
+                Area = string.Empty,
+                Fragment = "hello=world",
+                Host = "contoso.com",
+                Protocol = "http"
+            };
+
+            // Act
+            await anchorTagHelper.ProcessAsync(context, output);
+
+            // Assert
+            generator.Verify();
+
+            Assert.Equal("a", output.TagName);
+            Assert.Empty(output.Attributes);
+            Assert.True(output.Content.IsEmpty);
+        }
+
         [Theory]
         [InlineData("Action")]
         [InlineData("Controller")]
@@ -221,7 +393,7 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
 
             var expectedErrorMessage = "Cannot override the 'href' attribute for <a>. An <a> with a specified " +
                                        "'href' must not have attributes starting with 'asp-route-' or an " +
-                                       "'asp-action', 'asp-controller', 'asp-route', 'asp-protocol', 'asp-host', or " +
+                                       "'asp-action', 'asp-controller', 'asp-area', 'asp-route', 'asp-protocol', 'asp-host', or " +
                                        "'asp-fragment' attribute.";
 
             var context = new TagHelperContext(

test/Microsoft.AspNetCore.Mvc.TagHelpers.Test/FormTagHelperTest.cs

@@ -283,6 +283,175 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
             Assert.Empty(output.PostContent.GetContent());
         }
 
+        [Fact]
+        public async Task ProcessAsync_AspAreaAddsAreaToRouteValues()
+        {
+            // Arrange
+            var viewContext = CreateViewContext();
+            var context = new TagHelperContext(
+                allAttributes: new TagHelperAttributeList(
+                    Enumerable.Empty<TagHelperAttribute>()),
+                items: new Dictionary<object, object>(),
+                uniqueId: "test");
+            var output = new TagHelperOutput(
+                "form",
+                attributes: new TagHelperAttributeList(),
+                getChildContentAsync: (useCachedResult, encoder) =>
+                {
+                    var tagHelperContent = new DefaultTagHelperContent();
+                    tagHelperContent.SetContent("Something");
+                    return Task.FromResult<TagHelperContent>(tagHelperContent);
+                });
+
+            var expectedRouteValues = new Dictionary<string, object> { { "area", "Admin" } };
+            var generator = new Mock<IHtmlGenerator>(MockBehavior.Strict);
+            generator
+                .Setup(mock => mock.GenerateForm(
+                    viewContext,
+                    "Index",
+                    "Home",
+                    expectedRouteValues,
+                    null,
+                    null))
+                .Returns(new TagBuilder("form"))
+                .Verifiable();
+            var formTagHelper = new FormTagHelper(generator.Object)
+            {
+                Action = "Index",
+                Antiforgery = false,
+                Controller = "Home",
+                Area = "Admin",
+                ViewContext = viewContext,
+            };
+
+            // Act
+            await formTagHelper.ProcessAsync(context, output);
+
+            // Assert
+            generator.Verify();
+
+            Assert.Equal("form", output.TagName);
+            Assert.Equal(TagMode.StartTagAndEndTag, output.TagMode);
+            Assert.Empty(output.Attributes);
+            Assert.Empty(output.PreElement.GetContent());
+            Assert.Empty(output.PreContent.GetContent());
+            Assert.True(output.Content.IsEmpty);
+            Assert.Empty(output.PostContent.GetContent());
+        }
+
+        [Fact]
+        public async Task ProcessAsync_EmptyStringOnAspAreaIsPassedThroughToRouteValues()
+        {
+            // Arrange
+            var viewContext = CreateViewContext();
+            var context = new TagHelperContext(
+                allAttributes: new TagHelperAttributeList(
+                    Enumerable.Empty<TagHelperAttribute>()),
+                items: new Dictionary<object, object>(),
+                uniqueId: "test");
+            var output = new TagHelperOutput(
+                "form",
+                attributes: new TagHelperAttributeList(),
+                getChildContentAsync: (useCachedResult, encoder) =>
+                {
+                    var tagHelperContent = new DefaultTagHelperContent();
+                    tagHelperContent.SetContent("Something");
+                    return Task.FromResult<TagHelperContent>(tagHelperContent);
+                });
+
+            var expectedRouteValues = new Dictionary<string, object> { { "area", string.Empty } };
+            var generator = new Mock<IHtmlGenerator>(MockBehavior.Strict);
+            generator
+                .Setup(mock => mock.GenerateForm(
+                    viewContext,
+                    "Index",
+                    "Home",
+                    expectedRouteValues,
+                    null,
+                    null))
+                .Returns(new TagBuilder("form"))
+                .Verifiable();
+            var formTagHelper = new FormTagHelper(generator.Object)
+            {
+                Action = "Index",
+                Antiforgery = false,
+                Controller = "Home",
+                Area = string.Empty,
+                ViewContext = viewContext,
+            };
+
+            // Act
+            await formTagHelper.ProcessAsync(context, output);
+
+            // Assert
+            generator.Verify();
+
+            Assert.Equal("form", output.TagName);
+            Assert.Equal(TagMode.StartTagAndEndTag, output.TagMode);
+            Assert.Empty(output.Attributes);
+            Assert.Empty(output.PreElement.GetContent());
+            Assert.Empty(output.PreContent.GetContent());
+            Assert.True(output.Content.IsEmpty);
+            Assert.Empty(output.PostContent.GetContent());
+        }
+
+        [Fact]
+        public async Task ProcessAsync_AspAreaOverridesAspRouteArea()
+        {
+            // Arrange
+            var viewContext = CreateViewContext();
+            var context = new TagHelperContext(
+                allAttributes: new TagHelperAttributeList(
+                    Enumerable.Empty<TagHelperAttribute>()),
+                items: new Dictionary<object, object>(),
+                uniqueId: "test");
+            var output = new TagHelperOutput(
+                "form",
+                attributes: new TagHelperAttributeList(),
+                getChildContentAsync: (useCachedResult, encoder) =>
+                {
+                    var tagHelperContent = new DefaultTagHelperContent();
+                    tagHelperContent.SetContent("Something");
+                    return Task.FromResult<TagHelperContent>(tagHelperContent);
+                });
+
+            var expectedRouteValues = new Dictionary<string, object> { { "area", "Admin" } };
+            var generator = new Mock<IHtmlGenerator>(MockBehavior.Strict);
+            generator
+                .Setup(mock => mock.GenerateForm(
+                    viewContext,
+                    "Index",
+                    "Home",
+                    expectedRouteValues,
+                    null,
+                    null))
+                .Returns(new TagBuilder("form"))
+                .Verifiable();
+            var formTagHelper = new FormTagHelper(generator.Object)
+            {
+                Action = "Index",
+                Antiforgery = false,
+                Controller = "Home",
+                Area = "Admin",
+                RouteValues = new Dictionary<string, string> { { "area", "Client" } },
+                ViewContext = viewContext,
+            };
+
+            // Act
+            await formTagHelper.ProcessAsync(context, output);
+
+            // Assert
+            generator.Verify();
+
+            Assert.Equal("form", output.TagName);
+            Assert.Equal(TagMode.StartTagAndEndTag, output.TagMode);
+            Assert.Empty(output.Attributes);
+            Assert.Empty(output.PreElement.GetContent());
+            Assert.Empty(output.PreContent.GetContent());
+            Assert.True(output.Content.IsEmpty);
+            Assert.Empty(output.PostContent.GetContent());
+        }
+
         [Fact]
         public async Task ProcessAsync_CallsIntoGenerateRouteFormWithExpectedParameters()
         {
@@ -415,7 +584,7 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
 
             var expectedErrorMessage = "Cannot override the 'action' attribute for <form>. A <form> with a specified " +
                                        "'action' must not have attributes starting with 'asp-route-' or an " +
-                                       "'asp-action' or 'asp-controller' or 'asp-route' attribute.";
+                                       "'asp-action' or 'asp-controller' or 'asp-area' or 'asp-route' attribute.";
 
             var context = new TagHelperContext(
                 allAttributes: new TagHelperAttributeList(