Fix PageRouteTransformerConvention with custom page routes (#8576)

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

@@ -129,8 +129,10 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
             var pageRouteMetadata = selectorModel.EndpointMetadata.OfType<PageRouteMetadata>().SingleOrDefault();
             if (pageRouteMetadata == null)
             {
-                // Selector does not have expected metadata. Should never reach here
+                // Selector does not have expected metadata
-                throw new InvalidOperationException("Page selector did not have page route metadata.");
+                // This selector was likely configured by AddPageRouteModelConvention
+                // Use the existing explicitly configured template
+                return selectorModel.AttributeRouteModel.Template;
             }
 
             var segments = pageRouteMetadata.PageRoute.Split('/');

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

@@ -147,6 +147,18 @@ namespace Microsoft.AspNetCore.Mvc.FunctionalTests
             Assert.Equal("Hello from World", body);
         }
 
+        [Fact]
+        public async Task Page_PageRouteTransformer_PageWithConfiguredRoute()
+        {
+            // Arrange & Act
+            var response = await Client.GetAsync("http://localhost/PageRouteTransformer/NewConventionRoute/World");
+
+            // Assert
+            Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+            var body = await response.Content.ReadAsStringAsync();
+            Assert.Equal("Hello from World", body);
+        }
+
         [Fact]
         public virtual async Task ConventionalRoutedController_ActionIsReachable()
         {

test/WebSites/RoutingWebSite/Pages/LGAnotherPage.cshtml

@@ -1,4 +1,2 @@
 @page "{id?}"
 @model RoutingWebSite.Pages.LGAnotherPageModel
-@{
-}

test/WebSites/RoutingWebSite/Pages/LGPage.cshtml

@@ -1,4 +1,2 @@
 @page "{id?}"
 @model BasicWebSite.Pages.LGPageModel
-@{
-}

test/WebSites/RoutingWebSite/Pages/PageRouteTransformer/Index.cshtml

@@ -1,3 +1 @@
 @page
-@{
-}

test/WebSites/RoutingWebSite/Pages/PageRouteTransformer/PageWithConfiguredRoute.cshtml

@@ -0,0 +1,2 @@
+@page "ExtraPath/{id?}"
+Hello from @ViewContext.RouteData.Values["id"]

test/WebSites/RoutingWebSite/Pages/PageRouteTransformer/TestPage.cshtml

@@ -1,4 +1,2 @@
 @page "ExtraPath/{id?}"
-@{
-}
 Hello from @ViewContext.RouteData.Values["id"]

test/WebSites/RoutingWebSite/Startup.cs

@@ -28,6 +28,7 @@ namespace RoutingWebSite
                 })
                 .AddRazorPagesOptions(options =>
                 {
+                    options.Conventions.AddPageRoute("/PageRouteTransformer/PageWithConfiguredRoute", "/PageRouteTransformer/NewConventionRoute/{id?}");
                     options.Conventions.AddFolderRouteModelConvention("/PageRouteTransformer", model =>
                     {
                         pageRouteTransformerConvention.Apply(model);

test/WebSites/RoutingWebSite/StartupWith21Compat.cs

@@ -26,6 +26,7 @@ namespace RoutingWebSite
                 .AddMvc()
                 .AddRazorPagesOptions(options =>
                 {
+                    options.Conventions.AddPageRoute("/PageRouteTransformer/PageWithConfiguredRoute", "/PageRouteTransformer/NewConventionRoute/{id?}");
                     options.Conventions.AddFolderRouteModelConvention("/PageRouteTransformer", model =>
                     {
                         pageRouteTransformerConvention.Apply(model);