import Foundation

class A {}
struct B {}
protocol P {
    associatedtype C
    associatedtype D
}

class E<T: P> where T.C == A {
    enum Hoge {
        case a
    }

    func foo(completion: @escaping (A) -> Void) {
        bar(hoge: .a, completion: completion)
    }

    func bar(hoge: Hoge, completion: @escaping (T.D) -> Void) {
    }
}

x.swift:16:20: error: member 'a' in 'E<_>.Hoge' produces result of type 'E<T>.Hoge', but context expects 'E<_>.Hoge'
        bar(hoge: .a, completion: completion)
                   ^