extension Optional {
  /// Represents that an `Optional` was `nil`.
  public struct UnwrapError: Swift.Error & Equatable {
    public init() { }
  }

  @inlinable public var wrappedValue: Wrapped {
     get throws(UnwrapError) {
      switch self {
      case let wrapped?: return wrapped
      case nil: throw UnwrapError()
      }
    }
  }
}

struct GenericError<T>: Error {
  init() { }
}

struct S<T> {
  var property: Void {
    get throws(GenericError<Void>) { }
  }

  func method() throws(GenericError<Void>) { }
}

struct S<T> {
  var property: Void {
    get throws(GenericError<T>) { }
  }

  func method() throws(GenericError<T>) { }
}