Can't get c++ library to use the correct compiler

Using Swift
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1

I’m trying to use a system library written in C++ in my swift app on linux. Every time I try to build I get an error saying that the header “functional” does not exist. I’ve made a simple example package with a c++ module that only uses functional just to test, and now I’m convinced that swift is trying to compile it with a normal c compiler.

Package.swift

// swift-tools-version: 5.10

import PackageDescription

let package = Package(
    name: "myapp",
    products: [
        .executable(
            name: "myapp",
            targets: ["myapp"])
    ],
    targets: [
        .executableTarget(
            name: "myapp",
            dependencies: [
                "libmyexample"
            ]),
        .systemLibrary(
            name: "libmyexample"),
    ],
    cxxLanguageStandard: .cxx14
)

module.modulemap

module libmyexample [system] {
    header "libmyexample.hpp"

    export *
}

libmyexample.hpp

#include <functional>

class Example {
public:
    int memberFunction(int x) {
        return x;
    }
};

int callMemberFunction() {
    Example example;
    auto boundFunc = std::bind(&Example::memberFunction, &example, std::placeholders::_1);
    return boundFunc(30);
}

These are the errors I’m getting when running swift build:

Building for debugging...
error: emit-module command failed with exit code 1 (use -v to see invocation)
<module-includes>:1:10: note: in file included from <module-includes>:1:
#include "libmyexample.hpp"
         ^
/home/hbaker/TestCXXImport/Sources/libmyexample/libmyexample.hpp:1:10: error: 'functional' file not found
#include <functional>
         ^
/home/hbaker/TestCXXImport/Sources/myapp/main.swift:1:8: error: could not build C module 'libmyexample'
import libmyexample
       ^
<module-includes>:1:10: note: in file included from <module-includes>:1:
#include "libmyexample.hpp"
         ^
/home/hbaker/TestCXXImport/Sources/libmyexample/libmyexample.hpp:1:10: error: 'functional' file not found
#include <functional>
         ^
/home/hbaker/TestCXXImport/Sources/myapp/main.swift:1:8: error: could not build C module 'libmyexample'
import libmyexample
       ^
error: fatalError

I’ve also tested to see if classes alone work, but I get this error about the class as well:

/home/hbaker/TestCXXImport/Sources/libmyexample/libmyexample.hpp:3:1: error: unknown type name 'class'
class Example {
^

I can’t find any way to force swift to use the c++ compiler instead. I’ve tried the cxxLanguageStandard: .cxx14 line in Package.swift but that had no effect. I’ve also tried requiring cplusplus14 in the module map, but it fails to build saying module 'libmyexample' requires feature ‘cplusplus14’.

2

Take a look at the doc, it appears you're missing some steps from there.

3

Whoops, I completely forgot about the interoperabilityMode setting. Thanks.