Correct Endpoint ignored by EndpointRoutingMiddleware

Describe the bug

In UseEndpoints, I have a custom MapBlog and mvc route mappings

The MapBlog maps blog/{**slug} to a new IApplicationBuilder which uses a proxy middleware.

Some of the route mappings contain multiple constraints, and this somehow removes blog/{**slug} from consideration.

Example of this: {a:regex(^defaultValue$}/{b:regex(^defaultValue$}

In reality the endpoints in my project are more complex than this, but this is enough to reproduce

To Reproduce

https://github.com/serenata-keith-mifsud/AspNetCore3.1RoutingIssue

static async Task EmptyResponse(HttpContext context)
            {
                await context.Response.WriteAsync($"Hello World from {context.GetEndpoint().DisplayName}!");
            }

app.UseEndpoints(endpoints =>
            {
                endpoints.Map("blog/{**blog}", endpoints.CreateApplicationBuilder().Use(next => EmptyResponse).Build()).WithDisplayName("Blog");
                endpoints.MapControllerRoute("HomePage", "/", new { controller = "Home", action = "Index" }).WithDisplayName("HomePage");
                endpoints.MapControllerRoute("TwoConstraints", "{a:regex(^a$)}/{b:regex(^b$)}", new { controller = "Home", action = "Index" }).WithDisplayName("TwoConstaints");
            });

Microsoft.AspNetCore.Routing.Matching.DfaMatcher: Debug: 1 candidate(s) found for the request path ‘/blog/post’ Microsoft.AspNetCore.Routing.Matching.DfaMatcher: Debug: Endpoint ‘TwoConstaints’ with route pattern ‘{a:regex(^a$)}/{b:regex(^b$)}’ was rejected by constraint ‘a’:‘Microsoft.AspNetCore.Routing.Constraints.RegexInlineRouteConstraint’ with value ‘blog’ for the request path ‘/blog/post’ Microsoft.AspNetCore.Routing.Matching.DfaMatcher: Debug: Endpoint ‘TwoConstaints’ with route pattern ‘{a:regex(^a$)}/{b:regex(^b$)}’ is not valid for the request path ‘/blog/post’ Microsoft.AspNetCore.Routing.EndpointRoutingMiddleware: Debug: Request did not match any endpoints

Further technical details

Runtime Environment: OS Name: Windows OS Version: 10.0.18362 OS Platform: Windows RID: win10-x64 Base Path: C:\Program Files\dotnet\sdk\3.1.100\

Host (useful for support): Version: 3.1.0 Commit: 65f04fb6db

.NET Core SDKs installed: 2.0.2 [C:\Program Files\dotnet\sdk] 2.1.202 [C:\Program Files\dotnet\sdk] 2.1.509 [C:\Program Files\dotnet\sdk] 2.1.802 [C:\Program Files\dotnet\sdk] 2.2.402 [C:\Program Files\dotnet\sdk] 3.0.100 [C:\Program Files\dotnet\sdk] 3.1.100 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed: Microsoft.AspNetCore.All 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All] Microsoft.AspNetCore.All 2.1.14 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All] Microsoft.AspNetCore.All 2.2.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All] Microsoft.AspNetCore.All 2.2.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All] Microsoft.AspNetCore.App 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 2.1.14 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 2.2.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 2.2.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 3.0.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.NETCore.App 2.0.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 2.1.14 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 2.2.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 2.2.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 3.0.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.WindowsDesktop.App 3.0.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App] Microsoft.WindowsDesktop.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

IDE: Microsoft Visual Studio Professional 2019 Version 16.4.0

[serenata-keith-mifsud]

Yes thank you, had to use the switch as described here https://github.com/dotnet/aspnetcore/issues/21114

[mkArtakMSFT]

This should already be fixed in the latest 3.1 patch.