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

[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_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 <filesystem>

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 <stdio.h>
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.