Mingw: `mingw_unicode()` doesn't always fix undefined references to WinMain

[aminya]

https://github.com/aminya/cpp_vcpkg_project/pull/9

I have written a macro in project_options to try to fix the WinMain issue in MinGW. But adding -municode as a compile option doesn't fix the issue. Adding it as a link option causes linking to the fail with undefined reference to wWinMain. Other compilers don't need such flags, and I am not sure why we should do this for MinGW.

macro(mingw_unicode)
  is_mingw(_is_mingw)
  if(${_is_mingw})
    include(CheckCXXCompilerFlag)
    check_cxx_compiler_flag("-municode" _cxx_supports_municode)
    if(${_cxx_supports_municode})
      message(STATUS "Enabling Unicode for MinGW in the current project to fix undefined references to WinMain")
      add_compile_definitions("UNICODE" "_UNICODE")
      add_compile_options("-municode")
    endif()
  endif()
endmacro()

https://github.com/aminya/cpp_vcpkg_project/runs/6542106054?check_suite_focus=true#step:6:203

[6/18] Linking CXX executable my_exe\test\Debug\my_exe_helpers_tests.exe
FAILED: my_exe/test/Debug/my_exe_helpers_tests.exe 
cmd.exe /C "cd . && C:\Users\runneradmin\gcc\mingw64\bin\g++.exe -g  my_exe/test/CMakeFiles/my_exe_helpers_tests.dir/Debug/tests.cpp.obj -o my_exe\test\Debug\my_exe_helpers_tests.exe -Wl,--out-implib,my_exe\test\Debug\libmy_exe_helpers_tests.dll.a -Wl,--major-image-version,0,--minor-image-version,0  vcpkg_installed/x64-mingw-static/debug/lib/libfmtd.a  --coverage  -lkernel32 -luser32 -lgdi32 -lwinspool -lshell32 -lole32 -loleaut32 -luuid -lcomdlg32 -ladvapi32 && cd ."
c:/users/runneradmin/gcc/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/11.3.0/../../../../x86_64-w64-mingw32/bin/ld.exe: c:/users/runneradmin/gcc/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/11.3.0/../../../../x86_64-w64-mingw32/lib/../lib/libmingw32.a(lib64_libmingw32_a-crt0_c.o):crt0_c.c:(.text+0x46): undefined reference to `WinMain'
collect2.exe: error: ld returned 1 exit status
[7/18] Linking CXX executable my_lib\test\Debug\my_lib_tests.exe
FAILED: my_lib/test/Debug/my_lib_tests.exe my_lib/test/my_lib_tests_tests-84286ba.cmake D:/a/cpp_vcpkg_project/cpp_vcpkg_project/build/my_lib/test/my_lib_tests_tests-84286ba.cmake 
cmd.exe /C "cd . && C:\Users\runneradmin\gcc\mingw64\bin\g++.exe -g  my_lib/test/CMakeFiles/my_lib_tests.dir/Debug/tests.cpp.obj -o my_lib\test\Debug\my_lib_tests.exe -Wl,--out-implib,my_lib\test\Debug\libmy_lib_tests.dll.a -Wl,--major-image-version,0,--minor-image-version,0  my_lib/Debug/libmy_lib.a  --coverage  vcpkg_installed/x64-mingw-static/debug/lib/libfmtd.a  -lkernel32 -luser32 -lgdi32 -lwinspool -lshell32 -lole32 -loleaut32 -luuid -lcomdlg32 -ladvapi32 && cmd.exe /C "cd /D D:\a\cpp_vcpkg_project\cpp_vcpkg_project\build\my_lib\test && C:\Users\runneradmin\cmake\cmake-3.23.1-windows-x86_64\bin\cmake.exe -D TEST_TARGET=my_lib_tests -D TEST_EXECUTABLE=D:/a/cpp_vcpkg_project/cpp_vcpkg_project/build/my_lib/test/Debug/my_lib_tests.exe -D TEST_EXECUTOR= -D TEST_WORKING_DIR=D:/a/cpp_vcpkg_project/cpp_vcpkg_project/build/my_lib/test -D TEST_SPEC= -D TEST_EXTRA_ARGS= -D TEST_PROPERTIES= -D TEST_PREFIX= -D TEST_SUFFIX= -D TEST_LIST=my_lib_tests_TESTS -D TEST_REPORTER=xml -D TEST_OUTPUT_DIR= -D TEST_OUTPUT_PREFIX= -D TEST_OUTPUT_SUFFIX= -D CTEST_FILE=D:/a/cpp_vcpkg_project/cpp_vcpkg_project/build/my_lib/test/my_lib_tests_tests-84286ba.cmake -P D:/a/cpp_vcpkg_project/cpp_vcpkg_project/build/vcpkg_installed/x64-mingw-static/share/catch2/CatchAddTests.cmake""
c:/users/runneradmin/gcc/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/11.3.0/../../../../x86_64-w64-mingw32/bin/ld.exe: c:/users/runneradmin/gcc/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/11.3.0/../../../../x86_64-w64-mingw32/lib/../lib/libmingw32.a(lib64_libmingw32_a-crt0_c.o):crt0_c.c:(.text+0x46): undefined reference to `WinMain'
collect2.exe: error: ld returned 1 exit status
[8/18] Building CXX object my_header_lib/test/constexpr/CMakeFiles/my_header_lib_relaxed_constexpr_tests.dir/Debug/constexpr_tests.cpp.obj
Checking D:\a\cpp_vcpkg_project\cpp_vcpkg_project\my_header_lib\test\constexpr\constexpr_tests.cpp ...
Checking D:\a\cpp_vcpkg_project\cpp_vcpkg_project\my_header_lib\test\constexpr\constexpr_tests.cpp: CATCH_CONFIG_MAIN=1;CATCH_CONFIG_RUNTIME_STATIC_REQUIRE=1;FMT_LOCALE=1;UNICODE=1;_UNICODE=1;CMAKE_INTDIR="Debug"...
ninja: build stopped: subcommand failed.
task: Failed to run task "coverage": task: Failed to run task "build_template": exit status 1

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[aminya]

Reported here: https://sourceforge.net/p/mingw-w64/bugs/942/

[aminya]

This is a catch2 bug. This can be fixed by defining DO_NOT_USE_WMAIN when using catch2.