@propertyWrapper
struct PropertyWrapper<Wrapped> { var wrappedValue: Wrapped }

protocol SomeProtocol {
    
    typealias SpecializedPropertyWrapper<Wrapped> = PropertyWrapper<Wrapped>
    
}

struct SomeConformingType: SomeProtocol { }

struct AStruct {
    
    @SomeConformingType.SpecializedPropertyWrapper var string: String // unknown attribute 'SomeConformingType.SpecializedPropertyWrapper'
    
}