Add ability to modify UseRouting/UseEndpoint behavior for WebApplicationBuilder

[BrennanConroy]

Fixes #35147
Fixes #35281
Pre-req for #34146

UseRouting will not replace the EndpointRouteBuilder if a "global" one exists, this allows us to set a global one that will effectively ignore users calling UseRouting a second time (or multiple times themselves) so we can have all routes on the same route builder.

UseEndpoints also honors the global builder so it wont throw in some of it's checks that were specific to the default route builder.

Lastly, we use the new global route builder concept in WebApplicationBuilder so we can safely wrap users code in UseRouting/UseEndpoints and put all routes onto a single route builder.

[davidfowl]

We also need to avoid copying the __GlobalEndpointRouteBuilder properties when we call ApplicationBuilder.New(). We only need to do this in the WebApplication implementation though.

[davidfowl]

I think we should leave this (possibly).

Suggested change

_builtApplication.Properties.Remove(WebApplication.GlobalEndpointRouteBuilderKey);

[davidfowl]

After playing with this, here's another scenario that's broken that we need to preserve. The scenario here is that I have a static file called /foo.txt in the wwwroot:

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.UseStaticFiles();

app.UseRouting();

app.MapGet("/foo.txt", () => "This is a route");

app.Run();

After this change, we'll get "This is a route", if I hit /foo.txt instead of "This is a static file". This is because we unconditionally add UseRouting. We need to not call UseRouting if it's already been called because that lets the user control when route matching happens if they want to.

[javiercn]

After this change, we'll get "This is a route", if I hit /foo.txt instead of "This is a static file". This is because we unconditionally add UseRouting. We need to not call UseRouting if it's already been called because that lets the user control when route matching happens if they want to

That's a good catch we didn't thought of.

There are two questions:

• Implicit routing and teaching middleware about it (should static files know that the route decision was made implicitly and to serve the file even though and endpoint was set?)
• Should we cave in and avoid implicit routing? (Add the extra use routing call explicitly at the right time and do the UseEndpoints implicitly)

[davidfowl]

Implicit routing and teaching middleware about it (should static files know that the route decision was made implicitly and to serve the file even though and endpoint was set?)

I like this, but in .NET 7.

Should we cave in and avoid implicit routing? (Add the extra use routing call explicitly at the right time and do the UseEndpoints implicitly)

No I think we should do what we did before. Only add the implicit UseRouting if it's not defined by the application. This means we need a way to detect if it's been called.

[javiercn]

No I think we should do what we did before. Only add the implicit UseRouting if it's not defined by the application. This means e need a way to detect if it's been called.

Can we do that? (Is that something we get to do with the "double pipeline" trick?

[davidfowl]

Can we do that? (Is that something we get to do with the "double pipeline" trick?

I think we'd just update the call to UseRouting to set another property in the app builder so we can detect it. This is what we were doing previously.

[davidfowl]

We don't have coverage for this? File an issue.

[BrennanConroy]

#35423