Only use keyed services when keyed service provider is available

[captainsafia]

We should make sure that our keyed services implementations in the framework (SignalR, minimal APIs, MVC) all check that the target service provider supports keyed DI before resolving a keyed service from it.

[adityamandaleeka]

@benjaminpetit Can you look into this in RC2?

[BrennanConroy]

SignalR is handling this in #50248

[benjaminpetit]

MVC already do in #50145, but there is no clear exception message like for SignalR

[captainsafia]

MVC already do in #50145, but there is no clear exception message like for SignalR

How do we do this in MVC currently? I couldn't spot where we are throwing the exception from the changes in this PR.

In any case, maybe we stick this in 9.0 for now? @benjaminpetit What's the experience for users using a non-keyed service provider with keyed services? NotImplementedException?

[BrennanConroy]

Isn't it here:

aspnetcore/src/Mvc/Mvc.Core/src/ModelBinding/Binders/KeyedServicesModelBinder.cs

Lines 25 to 27 in 2335aa5

	if (keyedServices == null)
	{
	bindingContext.Result = ModelBindingResult.Failed();

[benjaminpetit]

Yes that's how it is handled. I think it's sufficient, but maybe we should do a check at startup?

[captainsafia]

Yeah, that approach is fine. We should probably set an error in the ModelState to indicate why the binding failed but that's fine to do as a follow-up.

It looks like we still need to add this check for minimal APIs. I assume it's not urgent enough for RC2?