RedirectToPage doesn't trim /Index from URL

Fixes #6080

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

@@ -88,6 +88,8 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
                         Name = selector.AttributeRouteModel.Name,
                         Order = selector.AttributeRouteModel.Order ?? 0,
                         Template = selector.AttributeRouteModel.Template,
+                        SuppressLinkGeneration = selector.AttributeRouteModel.SuppressLinkGeneration,
+                        SuppressPathMatching = selector.AttributeRouteModel.SuppressPathMatching,
                     },
                     DisplayName = $"Page: {model.ViewEnginePath}",
                     FilterDescriptors = filters,
@@ -95,7 +97,7 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
                     RelativePath = model.RelativePath,
                     RouteValues = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase)
                     {
-                        { "page", model.ViewEnginePath},
+                        { "page", model.ViewEnginePath },
                     },
                     ViewEnginePath = model.ViewEnginePath,
                 });

src/Microsoft.AspNetCore.Mvc.RazorPages/Internal/PageSelectorModel.cs

@@ -20,11 +20,16 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
                     model.RelativePath));
             }
 
-            model.Selectors.Add(CreateSelectorModel(model.ViewEnginePath, routeTemplate));
+            var selectorModel = CreateSelectorModel(model.ViewEnginePath, routeTemplate);
+            model.Selectors.Add(selectorModel);
 
             var fileName = Path.GetFileName(model.RelativePath);
             if (string.Equals(IndexFileName, fileName, StringComparison.OrdinalIgnoreCase))
             {
+                // For pages ending in /Index.cshtml, we want to allow incoming routing, but
+                // force outgoing routes to match to the path sans /Index.
+                selectorModel.AttributeRouteModel.SuppressLinkGeneration = true;
+
                 var parentDirectoryPath = model.ViewEnginePath;
                 var index = parentDirectoryPath.LastIndexOf('/');
                 if (index == -1)

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

@@ -142,5 +142,33 @@ namespace Microsoft.AspNetCore.Mvc.FunctionalTests
             // Assert
             Assert.Equal(expected, response.Trim());
         }
+
+        [Fact]
+        public async Task RedirectFromPage_RedirectsToPathWithoutIndexSegment()
+        {
+            //Arrange
+            var expected = "/Redirects";
+
+            // Act
+            var response = await Client.GetAsync("/Redirects/Index");
+
+            // Assert
+            Assert.Equal(HttpStatusCode.Redirect, response.StatusCode);
+            Assert.Equal(expected, response.Headers.Location.ToString());
+        }
+
+        [Fact]
+        public async Task RedirectFromPage_ToIndex_RedirectsToPathWithoutIndexSegment()
+        {
+            //Arrange
+            var expected = "/Redirects";
+
+            // Act
+            var response = await Client.GetAsync("/Redirects/RedirectToIndex");
+
+            // Assert
+            Assert.Equal(HttpStatusCode.Redirect, response.StatusCode);
+            Assert.Equal(expected, response.Headers.Location.ToString());
+        }
     }
 }

test/WebSites/RazorPagesWebSite/Pages/Redirects/Index.cshtml

@@ -0,0 +1,7 @@
+@page "{formaction?}"
+@functions
+{
+    public IActionResult OnGet() => RedirectToPage();
+
+    public IActionResult OnGetRedirectToIndex() => RedirectToPage("/Redirects/Index");
+}