Interop: Cannot return `swift::Optional<swift::String>` from C++ function

[ADKaster]

Description

Is it intended that the bound types swift::Optional and swift::String cannot be used to return swift types to swift?

Attempting to do so results in the swift::Optional<T> for some T being replaced with Never

/Users/andrew/Source/test/swift-return-swift-type/exe/Helper.swift:5:11: error: 'getValue()' is unavailable: return type is unavailable in Swift
3 | func printThings()
4 | {
5 |     print(getValue())
  |           `- error: 'getValue()' is unavailable: return type is unavailable in Swift
6 |     print(getString())
7 | }

exe.getValue:2:13: note: 'getValue()' has been explicitly marked unavailable here
1 | @available(*, unavailable, message: "return type is unavailable in Swift")
2 | public func getValue() -> Never
  |             `- note: 'getValue()' has been explicitly marked unavailable here

/Users/andrew/Source/test/swift-return-swift-type/exe/Helper.swift:6:11: error: 'getString()' is unavailable: return type is unavailable in Swift
4 | {
5 |     print(getValue())
6 |     print(getString())
  |           `- error: 'getString()' is unavailable: return type is unavailable in Swift
7 | }
8 | 

exe.getString:2:13: note: 'getString()' has been explicitly marked unavailable here
1 | @available(*, unavailable, message: "return type is unavailable in Swift")
2 | public func getString() -> Never
  |             `- note: 'getString()' has been explicitly marked unavailable here

Reproduction

This test case requires a few files, which I have uploaded here:

https://github.com/ADKaster/swift-return-swift-type

The results can be reproduced with

cmake -B build -GNinja
cmake --build build
# or ninja -C build

In the example, a few things are happening:

• We have a shared library, shlib, with one swift file "Color.swift".
• The shlib exports a bridging header, "shlib-Swift.h"
• We have an executable, exe, that has a helper file, Helper.h
• The helper file exports two functions, getValue() and getString() that each return swift::Optional<T> for some T.
• The exe has a swift file, Helper.swift, that tries to print the return values of getValue() and getString()

Helper.h

#pragma once

#include "Color.h"
#include "shlib-Swift.h"

swift::Optional<int> getValue() noexcept;
swift::Optional<swift::String> getString() noexcept;

Helper.cpp

#include "Helper.h"

swift::Optional<int> getValue() noexcept { return swift::Optional<int>::some(42); }
swift::Optional<swift::String> getString() noexcept { return swift::Optional<swift::String>::none(); }

Helper.swift

import exe

func printThings()
{
    print(getValue())
    print(getString())
}

Expected behavior

The program should compile successfully and print "42\nnone\n"

Environment

swift-driver version: 1.113 Apple Swift version 6.0 (swiftlang-6.0.0.7.6 clang-1600.0.24.1)
Target: arm64-apple-macosx14.0

Additional information

No response

[Xazax-hun]

I will take a look at this.

[paaspaas00]

@Xazax-hun any news on this one?

[Xazax-hun]

Unfortunately, I am swamped with some other tasks at the moment. I hope to get back to this at some point but probably that would be in the Swift 6.3 timeframe. Are you blocked on this?