swift::Array & swift::String linker errors

Development C++ interoperability
1

Hi everyone,

When attempting to compile with swift::Array and swift::String, on both Mac and Windows, I receive linker errors.

For example...

#include "MyLibrary-Swift.h"

void foo() {
    auto array = swift::Array<float>::init();
    return; 
}

yields..

Undefined symbols for architecture arm64:
  "Swift.Array.init() -> [A]", referenced from:
      foo() in foo.cpp.o
  "type metadata accessor for Swift.Array", referenced from:
      foo() in foo.cpp.o
      foo() in foo.cpp.o
  "type metadata for Swift.Float", referenced from:
      foo() in foo.cpp.o
      foo() in foo.cpp.o
ld: symbol(s) not found for architecture arm64

On Windows, I would suspect a missing toolchain /bin .DLL, but on Mac, I am surprised to see this.

Is there perhaps some .dylib / library that must be linked against to gain access to swift::String and swift::Array?

The project is otherwise healthy, with large numbers of Swift types being used happily from the C++ code. It's just swift::Array and swift::String causing grief!

Toolchain (Mac): swift-6.0.1-RELEASE
Clang (Mac): Apple clang version 16.0.0 (clang-1600.0.26.3)

2

Potentially related: Attempting to work with an std::string generated in Swift, in C++, yields an EXCEPTION_ACCESS_VIOLATION on Windows, though it does appear to work well on Mac.

import CxxStdlib

func foo() -> std::string {
    return "Hello world"
}

#include "BarLib-swift.h"

void baz() {
    std::string fooString = BarLib::foo(); // -> EXCEPTION_ACCESS_VIOLATION
};

I feel like there might be some piece of the puzzle I am missing, with respect to getting stable std::string / swift::String / std::Array use in C++ interop. Keen to hear ideas from any wise members of the forum!

3

Could you try to link explicitly against libswiftCore.tbd (on macOS) and swiftCore.lib on Windows? That's the library that defines those missing symbols.

4

@egor.zhdan thank you for the reply and suggestion. I was not able to find libswiftCore.tbd anywhere in swift-6.0.1-RELEASE.xctoolchain, but I did find a libswiftCore.dylib in the macOS directory, and I understand them to be equivalent.

Linking against libswiftCore.dylib resolved the linker errors on Mac, and swiftCore.lib on Windows.

In hindsight this seems obvious - I appreciate your help.