CMake / Meson compiler flag Wno form

The purpose of compiler flag checks is to test if a flag is supported. Metabuild system (such as CMake and Meson) compiler flag checks must not test the “-Wno-” form of a warning flag. This is because several compilers including Clang, GCC, Intel oneAPI emit a “success” return code 0 for the “-Wno-” form of an unsupported flag.

Incorrect

check_compiler_flag(C "-Wno-badflag" has_flag)

cc = meson.get_compiler('c')
has_flag = cc.has_argument('-Wno-badflag')

The incorrect CMake and Meson example scripts above will in general always set “has_flag = true” for the “-Wno-” form of a warning flag.

Correct way

check_compiler_flag(C "-Wbadflag" has_flag)

if(has_flag)
  target_compile_options(myexe PRIVATE -Wbadflag)
endif()

cc = meson.get_compiler('c')
has_flag = cc.has_argument('-Wbadflag')

if has_flag
  executable('myexe', 'myexe.c', c_args : '-Wbadflag')
endif()