Should running C++ with swift test work? (Getting to hello world with C++ and Swift Package)

[carlynorama]

(XCode 15 beta 6, MacOS 14.0 Beta (23A5301h))

I have two projects:

• Swift + C++ together in an XCode project. Swift can see C++ fine, compiles and runs. No problem.

  • GitHub - carlynorama/CppInteropSimplestXCode: Try out including C++ in a Swift Project

• Swift Package with C++ library target and Swift library target with a Testing target. It uses an explicit module map (because I couldn't get the umbrella header style example to work, actually). It does not run tests.

module cxxLibrary {
    header "SimpleCxxFunctions.hpp"

    export *
}

• GitHub - carlynorama/CxxInteropLibrary: Project for trying out C++ Interop with Swift in the context of a Library
  When I run the test, either in Xcode via the GUI diamonds or the command line with swift test I get :

Building for debugging...
ld: Undefined symbols:
  _myFavoriteNumber, referenced from:
      InteropLibrary.NumberMaker.currentNumber() -> Swift.Int in NumberMaker.swift.o
clang: error: linker command failed with exit code 1 (use -v to see invocation)
[5/6] Linking CxxInteropLibraryPa…
error: fatalError

Package file:

// swift-tools-version: 5.9
// The swift-tools-version declares the minimum version of Swift required to build this package.

import PackageDescription

let package = Package(
    name: "CxxInteropLibrary",
    products: [
        .library(
            name: "cxxLibrary",
            targets: ["cxxLibrary"]),
        .library(
            name: "InteropLibrary",
            targets: ["InteropLibrary"])
    ],
    targets: [
        .target(
            name: "cxxLibrary"),
        .target(
            name: "InteropLibrary",
            dependencies: ["cxxLibrary"]),
            //swiftSettings: [.interoperabilityMode(.Cxx)]), have tried it both ways. 
        .testTarget(
            name: "CxxInteropLibraryTests",
            dependencies: ["InteropLibrary", "cxxLibrary"],
            swiftSettings: [.interoperabilityMode(.Cxx)])
    ]
)

Neither XCode nor the VScode extension flag any problems before the build.

Before I keep banging my head against this, should I even expect this to work with XCTests? If so is there something obvious I've done wrong?

Thank you.

[Alex_L (Alex Lorenz)]

It appears your Swift InteropLibrary target is not enabling interop and thus it thinks it is calling a C function, not a C++ function. This modified package manifest works for me locally and fixes the link issue:

let package = Package(
    name: "CxxInteropLibrary",
    products: [
        .library(
            name: "cxxLibrary",
            targets: ["cxxLibrary"]),
        .library(
            name: "InteropLibrary",
            targets: ["InteropLibrary"])
    ],
    targets: [
        .target(
            name: "cxxLibrary"),
        .target(
            name: "InteropLibrary",
            dependencies: ["cxxLibrary"],
            swiftSettings: [.interoperabilityMode(.Cxx)]),
        .testTarget(
            name: "CxxInteropLibraryTests",
            dependencies: ["InteropLibrary", "cxxLibrary"],
            swiftSettings: [.interoperabilityMode(.Cxx)])
    ]
)

[carlynorama]

Thank you. Returning that swiftSettings line to the Interop library worked!

I could have sworn I had tried that both ways but I must not have cleaned out the build folder.