Is your feature request related to a problem? Please describe.

Route parameters in an ASP.NET Core Web API can be marked as optional with a ?, e.g.,

app.MapGet("/test1/{foo?}", (string? foo) => foo ?? "none"); // "/test1" returns "none"

If a route parameter marked as optional is followed by a non-optional route segment, the optional annotation is ignored. E.g.,

app.MapGet("/test2/{foo?}/bar", (string? foo) => foo ?? "none"); // "/test2//bar" returns 404

It is not immediately obvious (to me at least) that it would not be possible to have an optional parameter within a route, and there is no run-time error or warning when doing this.

The behavior appears to be the same for nullable value types (e.g. int?).

Describe the solution you'd like

An analyzer that checks for routes containing optional parameters followed by non-optional route segments, and provides an appropriate warning.

I also couldn't find any mention in the documentation stating that this is not possible.

Additional context

Optional route parameters are allowed to be followed by other optional parameters, so the analyzer should consider this case. E.g.,

app.MapGet("/test3/{foo?}/{bar?}", (string? foo, string? bar) => foo ?? bar ?? "none"); // "/test3" returns "none"