Pre-Pitch: Explicit protocol fulfilment with the 'conformance' keyword

[tera]

+1 for the pitch. As a bike shed name also consider "conforming":

conforming func foo() {...}

@gwendal.roue

In some valid programs, the method that fulfills the conformance is not declared at a location where the compiler has enough static information to accept the conformance keyword. In the code below, we can't use the 'conformance' keyword here, because when Q.foo is compiled, the P protocol is not statically known to be conformed to.

protocol P { func foo() }
protocol Q { }
extension Q { func foo() { } } // <-
struct T: P, Q { }

I wonder how we handle this situation with override and could we do the same with conformance?