Outbound route parameter transformer not working on ASP.NET Core MVC unless I use attribute routing

Describe the bug

An outbound route parameter transformer works only when I use attribute routing. Instead, I think it makes more sense if it worked even with the default route.

To Reproduce

Register an outbound route parameter transformer like this.

services.AddMvc(options =>
{
    var routeParameterTransformer = new MyParameterTransformer();
    var routeConvention = new RouteTokenTransformerConvention(routeParameterTransformer);
    options.Conventions.Add(routeConvention);
}).SetCompatibilityVersion(CompatibilityVersion.Version_2_2);

Where MyParameterTransformer is an implementation of IOutboundParameterTransformer.

public class MyParameterTransformer : IOutboundParameterTransformer
{
    public string TransformOutbound(object value)
    {
        if (value as string == "Home") {
            return "Welcome";
        }
        return value?.ToString();
    }
}

Now, when I visit the path /Welcome I get a 404 when I should be able to see the homepage instead. It starts working only if I use [Route("[controller]")] on the HomeController, which is inconvenient for UI applications.

Expected behavior

I’d expect the route parameter transformer to work with any route defined in the Startup class but it seems I must rely on attribute routing to make it work.

[JamesNK]

The purpose of a transformer is to apply a consistent pattern to a parameter. For example, making the controller and action parameters use camel case.

Thanks for the feedback on the documentation. I’ve made changes here - https://github.com/aspnet/Docs/pull/9987

[BrightSoul]

Ok, cool, I’m closing this issue.