Update @inject to support keyed services

[javiercn]

We added support for keyed services on the runtime as part of dotnet/aspnetcore#50561. We should consider what syntax we want to use when this is exposed through the @inject directive.

Some options are:

• @inject Key Type PropertyName.
• @inject Type Key PropertyName.
• @inject Type(Key) PropertyName.

This would be for Blazor and Razor pages, since both added support for it.

[javiercn]

/cc @SteveSanderson @MackinnonBuck

[ebekker]

@inject Type("Key") PropertyName
@* or *@
@inject Type["Key"] PropertyName

But either way I think the key needs to be quoted to distinguish a literal string from a reference to a const, e.g.:

@inject Type(Global.ServiceKey) PropertyName
@* or *@
@inject Type[Global.ServiceKey] PropertyName

static class Global
{
    public const string ServiceKey = "Key";
}

[burkenyo]

Hi there, will this feature make it into .NET 8?

[david-at-solve]

Or maybe something like

@inject(Key = "MyKey") MyType MyName

which alignes more to the traditional

[Inject(Key = "MyKey")] private MyType MyName { get; set; }

?

Or as a general alternative it could be helpful to attach all kinds of attributes to the generated property, which could also be non-key-related ones. This could then look like this:
@inject [Key("MyKey"), OtherAttribute] MyType MyPropName

Of course you would have to rethink the name of the "key identifying attribute".