How to specify C++-module-implementation file in CMakeLists.txt?

Usage
1

Hello,
I posted the following at https://stackoverflow.com/q/79687866/5525302, but got no answer, that is why I try it here.

I want to create a c+±20-module without partitions but where the interface is in a different file than the implementation. This is my setup:

interface file ModuleTest.ixx:

export module moduleTest;
export int foo();

implementation file ModuleTest.cpp:

module moduleTest;
int foo() {
  // some implementation
}

How do I need to specify the implementation file within the corresponding target in CMakeLists.txt?

This is what I tried:

add_library(moduleTest)

target_sources(moduleTest
    PRIVATE FILE_SET CXX_MODULES FILES
    ModuleTest.ixx
    PRIVATE
    ModuleTest.cpp
)
target_compile_features(moduleTest PUBLIC cxx_std_20)
target_compile_options(moduleTest PRIVATE "-fmodules-ts")

I get this error:


moduleTest: error: failed to read compiled module: No such file or directory
moduleTest: note: compiled module file is 'gcm.cache/moduleTest.gcm'
moduleTest: note: imports must be built before being imported
moduleTest: fatal error: returning to the gate for a mechanical issue

Can I expect this to work at all? 

Thanks for any advice!
2

You may read C++20 Modules, CMake, And Shared Libraries