protocol P {
    associatedtype A
}
struct G<A>: P {}
protocol I {
    associatedtype A
    associatedtype C: P
    init(_: C)
}
struct F<C: P>: I {
    typealias A = C.A
    init(_: C) {}
}
extension I where C == G<Int> {
    static var int: Self { return .init(.init()) }
}
extension I where C == G<A>, A: Numeric {
    static var numeric: Self { return .init(.init()) }
}
func foo<C: P>(_: F<C>, a: C.A.Type = C.A.self) {}
func test() {
    // works when G.A is specified as a constraint on the extension
    foo(.int)
    // does not work when G.A is specified in the expression context
    foo(.numeric, a: Int.self) // Generic parameter 'C' could not be inferred
}