Inferring nested associated types with opaque return types

Inference.swift

protocol A { }

struct AImpl: A {
    init() { }
}

protocol B {
    associatedtype BA: A

    var a: BA { get }
}

struct BImpl: B {
    init() { }

    var a: some A {
        return AImpl()
    }
}

protocol C: B {
    associatedtype CB: B where BA == CB.BA

    var b: CB { get }
}

extension C {
    var a: BA {
        return b.a
    }
}

struct CImpl: C { // Type 'CImpl' does not conform to protocol 'B', wants to insert typealias for BA
    var b: some B {
        return BImpl()
    }
}

//struct CImpl: C { // 'C' requires the types 'CImpl.BA' (aka 'some A') and '(some B).BA' to be equivalent
//    typealias BA = BImpl.BA
//
//    var b: some B {
//        return BImpl()
//    }
//}

//struct CImpl: C { // Works but requires being explicit with types
//    typealias BA = BImpl.BA
//
//    var b: BImpl {
//        return BImpl()
//    }
//}