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

samples/TagHelperSample.Web/Areas/Admin/Views/Admin/Index.cshtml

@@ -0,0 +1,7 @@
+@*
+    For more information on enabling MVC for empty projects, visit http://go.microsoft.com/fwlink/?LinkID=397860
+*@
+@{
+}
+
+<a asp-action="Index" asp-controller="Home" asp-area="">Go home!</a>

samples/TagHelperSample.Web/Areas/Admin/Views/_ViewImports.cshtml

@@ -0,0 +1 @@
+@addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers

samples/TagHelperSample.Web/Controllers/AdminController.cs

@@ -0,0 +1,17 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Mvc;
+
+namespace TagHelperSample.Web.Controllers
+{
+    [Area("Admin")]
+    public class AdminController : Controller
+    {
+        public IActionResult Index()
+        {
+            return View();
+        }
+    }
+}

samples/TagHelperSample.Web/Controllers/HomeController.cs

@@ -37,6 +37,16 @@ public IActionResult Create()
             return View();
         }
 
+        // GET: /Home/Create
+        public IActionResult Link()
+        {
+            var pageLink = Url.Action("Index", new { page = (string)null });
+            var otherPageLink = Url.Action("Index", new { page = (string)"1" });
+            var yetAnotherPageLink = Url.Action("Index", new { page = "" });
+            return View();
+        }
+
+
         // POST: Home/Create
         [HttpPost]
         public IActionResult Create(User user)

samples/TagHelperSample.Web/Startup.cs

@@ -31,7 +31,20 @@ public void Configure(IApplicationBuilder app, ILoggerFactory loggerFactory)
 
             app.UseStaticFiles();
 
-            app.UseMvcWithDefaultRoute();
+            app.UseMvc(routes =>
+            {
+                routes.MapAreaRoute("Admin", "Admin", "Admin/{controller}/{action}", new
+                {
+                    controller = "Admin",
+                    action = "Index"
+                });
+
+                routes.MapRoute("Default", "{controller}/{action}", new
+                {
+                    controller = "Home",
+                    action = "Index"
+                });
+            });
         }
 
         public static void Main(string[] args)

samples/TagHelperSample.Web/Views/Home/Index.cshtml

@@ -24,6 +24,7 @@
 <script>bar();</script>
 
 <h2>Index</h2>
+<a asp-action="Index" asp-Controller="Admin" asp-area="Admin" asp-route-area="Yolo">Go to admin!</a>
 @if (Model != null && Model.Count() != 0)
 {
     <div class="form-horizontal">

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 @@ public class AnchorTagHelper : TagHelper
     {
         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 @@ public override int Order
         [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 @@ public override void Process(TagHelperContext context, TagHelperOutput output)
             {
                 if (Action != null ||
                     Controller != null ||
+                    Area != null ||
                     Route != null ||
                     Protocol != null ||
                     Host != null ||
@@ -159,6 +169,7 @@ public override void Process(TagHelperContext context, TagHelperOutput output)
                             "<a>",
                             ActionAttributeName,
                             ControllerAttributeName,
+                            AreaAttributeName,
                             RouteAttributeName,
                             ProtocolAttributeName,
                             HostAttributeName,
@@ -180,6 +191,18 @@ public override void Process(TagHelperContext context, TagHelperOutput output)
                     }
                 }
 
+                if (Area != null)
+                {
+                    if (routeValues == null)
+                    {
+                        routeValues = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase);
+                    }
+
+                    // If a user specifies asp-area and asp-route-area we want the first one to always win
+                    // so we unconditionally replace the value in the dictionary with that one.
+                    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 @@ public class FormTagHelper : TagHelper
     {
         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 @@ public override int Order
         [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 @@ public override void Process(TagHelperContext context, TagHelperOutput output)
             // 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 @@ public override void Process(TagHelperContext context, TagHelperOutput output)
                             HtmlActionAttributeName,
                             ActionAttributeName,
                             ControllerAttributeName,
+                            AreaAttributeName,
                             RouteAttributeName,
                             RouteValuesPrefix));
                 }
@@ -171,6 +180,18 @@ public override void Process(TagHelperContext context, TagHelperOutput output)
                     }
                 }
 
+                if (Area != null)
+                {
+                    if (routeValues == null)
+                    {
+                        routeValues = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase);
+                    }
+
+                    // If a user specifies asp-area and asp-route-area we want the first one to always win
+                    // so we unconditionally replace the value in the dictionary with that one.
+                    routeValues["area"] = Area;
+                }
+
                 TagBuilder tagBuilder;
                 if (Route == null)
                 {

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>