Raw route values should be restored after template binder failing binding values when generating a url

[Tratcher]

From @anobaka on December 6, 2016 7:20

Minimal repro steps

1. Create a sample .net core web application.
2. Modify the app.UseMvc... line to:

app.UseMvc(routes =>
{
    routes.MapRoute(
        name: "test",
        template: "{area?}/{controller=Home}/{action=Index}/{id?}"
    );
    routes.MapRoute(
        name: "default",
        template: "{controller=Home}/{action=Index}/{id?}");
});

3. Add TestController and an Index action in it.
4. Add var a = Url.Action("Index", "Test"); in Index Action of HomeController.
5. Run app and visit /.

Expected result

local variable a should be /Test

Actual result

the value of a is /

Further technical details

I checked the source of Routing and found that the raw route values will not be restored after template binder failed binding values. So when the default router was tring to generate url, there was action:Index only left in route values, so it used the default controller Home.
ref:
https://github.com/aspnet/Routing/blob/rel/1.1.0/src/Microsoft.AspNetCore.Routing/Template/TemplateBinder.cs#L238
https://github.com/aspnet/Routing/blob/rel/1.1.0/src/Microsoft.AspNetCore.Routing/Template/TemplateBinder.cs#L279
I think the logic is that all routers should try to bind raw route values to generate url, but not the route values modified by previous router, so the raw route values should be restored after each router binding or routers should use the copy of the raw route values.

Thanks.

Copied from original issue: dotnet/aspnetcore#1860

[javiercn]

@rynowak

[rynowak]

@Eilon - we should investigate this, if there's a bug here this is a good 1.1.1 candidate.

[Eilon]

I'm able to reproduce this and it definitely looks wrong.

[Eilon]

@kichalla can you investigate a fix for this? We're going to consider this for 1.1.1, so please don't merge until we get patch approval for this (especially depending on how risky the fix is).

[kichalla]

Looking into it now...