Fix #6140 - Allow linking between controller and page

The issue here is that route values used for action selection are
'global'. That means that pages need to have a 'null' route value for
'action' and controllers need to have a 'null' route value for pages. This
is the same way that areas work.

The fix is to move the 'merge' of route values up to a level where pages
and controllers can work together. Since ADPs use the russian-doll
pattern, the fix is to run this 'merge' in the controller ADP, but after
all of the ADs have been created.

src/Microsoft.AspNetCore.Mvc.Core/Internal/ControllerActionDescriptorBuilder.cs

@@ -34,8 +34,6 @@ namespace Microsoft.AspNetCore.Mvc.Internal
         {
             var actions = new List<ControllerActionDescriptor>();
 
-            var routeValueKeys = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
-
             var methodInfoMap = new MethodToActionMap();
 
             var routeTemplateErrors = new List<string>();
@@ -64,7 +62,7 @@ namespace Microsoft.AspNetCore.Mvc.Internal
                         actionDescriptor.ControllerTypeInfo = controller.ControllerType;
 
                         AddApiExplorerInfo(actionDescriptor, application, controller, action);
-                        AddRouteValues(routeValueKeys, actionDescriptor, controller, action);
+                        AddRouteValues(actionDescriptor, controller, action);
                         AddProperties(actionDescriptor, action, controller, application);
 
                         actionDescriptor.BoundProperties = controllerPropertyDescriptors;
@@ -108,12 +106,6 @@ namespace Microsoft.AspNetCore.Mvc.Internal
                     // attribute routes with a given name have the same template.
                     AddActionToNamedGroup(actionsByRouteName, attributeRouteInfo.Name, actionDescriptor);
                 }
-
-                // Add a route value with 'null' for each user-defined route value in the set to all the
-                // actions that don't have that value. For example, if a controller defines
-                // an area, all actions that don't belong to an area must have a route
-                // value that prevents them from matching an incoming request when area is specified.
-                AddGlobalRouteValues(actionDescriptor, routeValueKeys);
             }
 
             if (attributeRoutingConfigurationErrors.Any())
@@ -409,7 +401,6 @@ namespace Microsoft.AspNetCore.Mvc.Internal
         }
 
         public static void AddRouteValues(
-            ISet<string> keys,
             ControllerActionDescriptor actionDescriptor,
             ControllerModel controller,
             ActionModel action)
@@ -421,8 +412,6 @@ namespace Microsoft.AspNetCore.Mvc.Internal
             // generating a link.
             foreach (var kvp in action.RouteValues)
             {
-                keys.Add(kvp.Key);
-
                 // Skip duplicates
                 if (!actionDescriptor.RouteValues.ContainsKey(kvp.Key))
                 {
@@ -432,8 +421,6 @@ namespace Microsoft.AspNetCore.Mvc.Internal
 
             foreach (var kvp in controller.RouteValues)
             {
-                keys.Add(kvp.Key);
-
                 // Skip duplicates - this also means that a value on the action will take precedence
                 if (!actionDescriptor.RouteValues.ContainsKey(kvp.Key))
                 {
@@ -483,19 +470,6 @@ namespace Microsoft.AspNetCore.Mvc.Internal
             }
         }
 
-        private static void AddGlobalRouteValues(
-            ControllerActionDescriptor actionDescriptor,
-            ISet<string> removalConstraints)
-        {
-            foreach (var key in removalConstraints)
-            {
-                if (!actionDescriptor.RouteValues.ContainsKey(key))
-                {
-                    actionDescriptor.RouteValues.Add(key, string.Empty);
-                }
-            }
-        }
-
         private static void AddActionToNamedGroup(
             IDictionary<string, IList<ActionDescriptor>> actionsByRouteName,
             string routeName,

src/Microsoft.AspNetCore.Mvc.Core/Internal/ControllerActionDescriptorProvider.cs

@@ -66,6 +66,36 @@ namespace Microsoft.AspNetCore.Mvc.Internal
         /// <inheritdoc />
         public void OnProvidersExecuted(ActionDescriptorProviderContext context)
         {
+            // After all of the providers have run, we need to provide a 'null' for each all of route values that 
+            // participate in action selection.
+            //
+            // This is important for scenarios like Razor Pages, that use the 'page' route value. An action that
+            // uses 'page' shouldn't match when 'action' is set, and an action that uses 'action' shouldn't match when
+            // 'page is specified.
+            //
+            // Or for another example, consider areas. A controller that's not in an area needs a 'null' value for
+            // area so it can't match when the route produces an 'area' value.
+            var keys = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
+            for (var i = 0; i < context.Results.Count; i++)
+            {
+                var action = context.Results[i];
+                foreach (var key in action.RouteValues.Keys)
+                {
+                    keys.Add(key);
+                }
+            }
+
+            for (var i = 0; i < context.Results.Count; i++)
+            {
+                var action = context.Results[i];
+                foreach (var key in keys)
+                {
+                    if (!action.RouteValues.ContainsKey(key))
+                    {
+                        action.RouteValues.Add(key, null);
+                    }
+                }
+            }
         }
 
         internal protected IEnumerable<ControllerActionDescriptor> GetDescriptors()

src/Microsoft.AspNetCore.Mvc.RazorPages/Infrastructure/PageActionDescriptorProvider.cs

@@ -28,7 +28,7 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
             _pagesOptions = pagesOptionsAccessor.Value;
         }
 
-        public int Order { get; set; }
+        public int Order { get; set; } = -900; // Run after the default MVC provider, but before others.
 
         public void OnProvidersExecuting(ActionDescriptorProviderContext context)
         {

test/Microsoft.AspNetCore.Mvc.Core.Test/Internal/ControllerActionDescriptorProviderTests.cs

@@ -277,11 +277,11 @@ namespace Microsoft.AspNetCore.Mvc.Internal
 
             var descriptorWithoutValue = Assert.Single(
                 descriptors,
-                ad => ad.RouteValues.Any(kvp => kvp.Key == "key" && string.IsNullOrEmpty(kvp.Value)));
+                ad => !ad.RouteValues.ContainsKey("key"));
 
             var descriptorWithValue = Assert.Single(
                 descriptors,
-                ad => ad.RouteValues.Any(kvp => kvp.Key == "key" && kvp.Value == "value"));
+                ad => ad.RouteValues.ContainsKey("key"));
 
             // Assert
             Assert.Equal(2, descriptors.Length);
@@ -303,7 +303,7 @@ namespace Microsoft.AspNetCore.Mvc.Internal
                     c.Key == "key" &&
                     c.Value == "value");
 
-            Assert.Equal(3, descriptorWithoutValue.RouteValues.Count);
+            Assert.Equal(2, descriptorWithoutValue.RouteValues.Count);
             Assert.Single(
                 descriptorWithoutValue.RouteValues,
                 c =>
@@ -314,11 +314,6 @@ namespace Microsoft.AspNetCore.Mvc.Internal
                 c =>
                     c.Key == "action" &&
                     c.Value == "OnlyPost");
-            Assert.Single(
-                descriptorWithoutValue.RouteValues,
-                c =>
-                    c.Key == "key" &&
-                    c.Value == string.Empty);
         }
 
         [Fact]
@@ -932,7 +927,7 @@ namespace Microsoft.AspNetCore.Mvc.Internal
 
             var indexAction = Assert.Single(actionDescriptors, ad => ad.ActionName.Equals("Index"));
 
-            Assert.Equal(5, indexAction.RouteValues.Count);
+            Assert.Equal(3, indexAction.RouteValues.Count);
 
             var controllerDefault = Assert.Single(indexAction.RouteValues, rd => rd.Key.Equals("controller", StringComparison.OrdinalIgnoreCase));
             Assert.Equal("ConventionalAndAttributeRoutedActionsWithArea", controllerDefault.Value);
@@ -942,12 +937,6 @@ namespace Microsoft.AspNetCore.Mvc.Internal
 
             var areaDefault = Assert.Single(indexAction.RouteValues, rd => rd.Key.Equals("area", StringComparison.OrdinalIgnoreCase));
             Assert.Equal("Home", areaDefault.Value);
-
-            var mvRouteValueDefault = Assert.Single(indexAction.RouteValues, rd => rd.Key.Equals("key", StringComparison.OrdinalIgnoreCase));
-            Assert.Equal(string.Empty, mvRouteValueDefault.Value);
-
-            var anotherRouteValue = Assert.Single(indexAction.RouteValues, rd => rd.Key.Equals("second", StringComparison.OrdinalIgnoreCase));
-            Assert.Equal(string.Empty, anotherRouteValue.Value);
         }
 
         [Fact]
@@ -1355,6 +1344,42 @@ namespace Microsoft.AspNetCore.Mvc.Internal
             Assert.Single(action.ActionConstraints, a => a is ConstraintAttribute);
         }
 
+        [Fact]
+        public void OnProviderExecuted_AddsGlobalRouteValues()
+        {
+            // Arrange
+            var context = new ActionDescriptorProviderContext();
+            context.Results.Add(new ActionDescriptor()
+            {
+                RouteValues = new Dictionary<string, string>()
+                {
+                    { "controller", "Home" },
+                    { "action", "Index" },
+                }
+            });
+            context.Results.Add(new ActionDescriptor()
+            {
+                RouteValues = new Dictionary<string, string>()
+                {
+                    { "page", "/Some/Page" }
+                }
+            });
+
+            var provider = GetProvider();
+
+            // Act
+            provider.OnProvidersExecuted(context);
+
+            // Assert
+            Assert.True(context.Results[0].RouteValues.ContainsKey("page"));
+            Assert.Null(context.Results[0].RouteValues["page"]);
+
+            Assert.True(context.Results[1].RouteValues.ContainsKey("controller"));
+            Assert.Null(context.Results[1].RouteValues["controller"]);
+            Assert.True(context.Results[1].RouteValues.ContainsKey("action"));
+            Assert.Null(context.Results[1].RouteValues["action"]);
+        }
+
         private ControllerActionDescriptorProvider GetProvider(
             TypeInfo controllerTypeInfo,
             IEnumerable<IFilterMetadata> filters = null)

test/Microsoft.AspNetCore.Mvc.FunctionalTests/RazorPagesTest.cs

@@ -791,6 +791,34 @@ Microsoft.AspNetCore.Mvc.ViewFeatures.ViewDataDictionary`1[AspNetCore._InjectedP
             Assert.Equal(expected, response.Headers.Location.ToString());
         }
 
+        [Fact]
+        public async Task Controller_RedirectToPage()
+        {
+            // Arrange
+            var expected = "/RedirectToController?param=17";
+
+            // Act
+            var response = await Client.GetAsync("/RedirectToPage");
+
+            // Assert
+            Assert.Equal(HttpStatusCode.Redirect, response.StatusCode);
+            Assert.Equal(expected, response.Headers.Location.ToString());
+        }
+
+        [Fact]
+        public async Task Page_RedirectToController()
+        {
+            // Arrange
+            var expected = "/RedirectToPage?param=92";
+
+            // Act
+            var response = await Client.GetAsync("/RedirectToController");
+
+            // Assert
+            Assert.Equal(HttpStatusCode.Redirect, response.StatusCode);
+            Assert.Equal(expected, response.Headers.Location.ToString());
+        }
+
         private async Task AddAntiforgeryHeaders(HttpRequestMessage request)
         {
             var getResponse = await Client.GetAsync(request.RequestUri);

test/WebSites/RazorPagesWebSite/Controllers/RedirectController.cs

@@ -0,0 +1,16 @@
+// 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 Microsoft.AspNetCore.Mvc;
+
+namespace RazorPagesWebSite
+{
+    public class RedirectController : Controller
+    {
+        [HttpGet("/RedirectToPage")]
+        public IActionResult RedirectToPage()
+        {
+            return RedirectToRoute(new { page = "/RedirectToController", param = 17 });
+        }
+    }
+}

test/WebSites/RazorPagesWebSite/RedirectToController.cshtml

@@ -0,0 +1,8 @@
+@page
+
+@functions {
+    public IActionResult OnGet()
+    {
+        return new RedirectToRouteResult(new { controller = "Redirect", action = "RedirectToPage", param = 92 });
+    }
+}