when using modules - `CMake can not determine linker language for target: foo`

[shemeshg]

• error Files are not created for cppfront in the build folder

CMakeLists.txt

cmake_minimum_required(VERSION 3.28)
project(std_module_example CXX)

# Turning off extensions avoids an issue with the clang 16 compiler
# clang 17 and greater can avoid this setting
set(CMAKE_CXX_EXTENSIONS OFF)
# Set the version of C++ for the project
set(CMAKE_CXX_STANDARD 20)

add_subdirectory(cppfront)
# Create a library
add_library(foo)
# Add the module file to the library
target_sources(foo
  PUBLIC
    FILE_SET CXX_MODULES FILES
      foo.cpp2
)
# Create an executable
add_executable(hello main.cxx)
# Link to the library foo
target_link_libraries(hello foo cppfront)

main.cxx

import shalom;

int main()
{
  foo f;  
  f.helloworld();
  return 0;
}

foo.cpp2 (change to foo.cxx and it will work)

// Global module fragment where #includes can happen
module;
#include <iostream>

// first thing after the Global module fragment must be a module command
export module shalom;

export class foo {
public:
  foo();
  ~foo();
  void helloworld();
};

foo::foo() = default;
foo::~foo() = default;
void foo::helloworld() { std::cout << "hello world\n"; }

[alexreinking]

Aha looks like we have to scan the file sets too

[shemeshg]

also maybe authoring modules aren't supported yet:

hsutter/cppfront#1059

[alexreinking]

After merging #145, this build will work:

cmake_minimum_required(VERSION 3.29)
project(std_module_example CXX)

set(CMAKE_CXX_EXTENSIONS OFF)
set(CMAKE_CXX_STANDARD 20)

find_package(cppfront REQUIRED)

add_library(foo)
target_sources(
    foo
    PUBLIC
    FILE_SET CXX_MODULES
    FILES foo.cpp2
)

add_executable(main main.cxx)
target_link_libraries(main PRIVATE foo)