Statically linking an executable with JPEG XL enabled breaks the build at link time

[nightmareci]

I'm working on a project where I want to CMake-consume (via FetchContent), build, and statically link all the dependencies (SDL, all the satellite libraries) for distributed release builds. Enabling JPEG XL breaks the build though, as it needs C++, and C++ doesn't get enabled properly in this setup, so the build output throws a bunch of C++ linking errors. For now, adding an enable_language(CXX) gets it working, but that doesn't really seem correct, I don't think a CMake project (mine) consuming another (SDL_image) should have to do that, if my project's code doesn't include any C++. So, somehow, C++ needs to get enabled so the final statically linked executable can get the C++ code linked in.

I've encountered this bug with both SDL2 and SDL3.

[madebr]

This is a CMake quirk you're encountering. We do enable_language(CXX) in our cmake script. This sets the LINKER_LANGUAGE property of the SDL_image targets to CXX.

For some reason CMake needs enable_language(CXX) at the same (or higher) level when using any target that uses c++. I cannot immediately find an issue at CMake's issue tracker.

This minimal CMake project reproduces your issue:

C executable using a C++ static library

```cmake cmake_minimum_required(VERSION 3.25) project(masterproject LANGUAGES C) file(WRITE subproject/CMakeLists.txt [=====[ cmake_minimum_required(VERSION 3.25) project(subproject LANGUAGES C CXX) file(WRITE lib.cpp [=[ #include extern "C" { int exists(const char *filename) { std::error_code ec; return std::filesystem::exists(filename, ec); } } ]=]) add_library(sublibrary STATIC lib.cpp) target_link_libraries(sublibrary stdc++fs) set_property(TARGET sublibrary PROPERTY CXX_STANDARD 17) ]=====]) file(WRITE main.c [=[ #include extern int exists(const char *filename); int main(int argc, char *argv[]) { if (argc < 2) { fprintf(stderr, "Need argument\n"); return 1; } printf("Exists: %d\n", exists(argv[1])); return 0; } ]=]) add_subdirectory(subproject) add_executable(main main.c) target_link_libraries(main PRIVATE sublibrary) # Uncomment the following line to fix the link error # enable_language(CXX) ```

[madebr]

I'm closing this issue. Let's hope a future CMake release fixes this.