CMake/Modules/CheckCompilerFlag.cmake

# Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
# file Copyright.txt or https://cmake.org/licensing for details.

#[=======================================================================[.rst:
CheckCompilerFlag
---------------------

.. versionadded:: 3.19

Check whether the compiler supports a given flag.

.. command:: check_compiler_flag

  .. code-block:: cmake

    check_compiler_flag(<lang> <flag> <var>)

Check that the ``<flag>`` is accepted by the compiler without a diagnostic.
Stores the result in an internal cache entry named ``<var>``.

This command temporarily sets the ``CMAKE_REQUIRED_DEFINITIONS`` variable
and calls the ``check_source_compiles(<LANG>`` function from the
:module:`CheckSourceCompiles` module.  See documentation of that
module for a listing of variables that can otherwise modify the build.

A positive result from this check indicates only that the compiler did not
issue a diagnostic message when given the flag.  Whether the flag has any
effect or even a specific one is beyond the scope of this module.

.. note::
  Since the :command:`try_compile` command forwards flags from variables
  like :variable:`CMAKE_<LANG>_FLAGS <CMAKE_<LANG>_FLAGS>`, unknown flags
  in such variables may cause a false negative for this check.
#]=======================================================================]

include_guard(GLOBAL)
include(CheckSourceCompiles)
include(CMakeCheckCompilerFlagCommonPatterns)

cmake_policy(PUSH)
cmake_policy(SET CMP0054 NEW) # if() quoted variables not dereferenced
cmake_policy(SET CMP0057 NEW) # if() supports IN_LIST

function(CHECK_COMPILER_FLAG _lang _flag _var)

  if(_lang STREQUAL C)
    set(_lang_src "int main(void) { return 0; }")
    set(_lang_fail_regex FAIL_REGEX "command[ -]line option .* is valid for .* but not for C")
  elseif(_lang STREQUAL CXX)
    set(_lang_src "int main() { return 0; }")
    set(_lang_fail_regex FAIL_REGEX "command[ -]line option .* is valid for .* but not for C\\+\\+")
  elseif(_lang STREQUAL Fortran)
    set(_lang_src "       program test\n       stop\n       end program")
    set(_lang_fail_regex FAIL_REGEX "command[ -]line option .* is valid for .* but not for Fortran")
  elseif(_lang STREQUAL OBJC)
    set(_lang_src [=[
#ifndef __OBJC__
#  error "Not an Objective-C compiler"
#endif
int main(void) { return 0; }]=])
    set(_lang_fail_regex FAIL_REGEX "command[ -]line option .* is valid for .* but not for Objective-C" # GNU
                         FAIL_REGEX "argument unused during compilation: .*") # Clang
  elseif(_lang STREQUAL OBJCXX)
    set(_lang_src [=[
#ifndef __OBJC__
#  error "Not an Objective-C++ compiler"
#endif
int main(void) { return 0; }]=])
    set(_lang_fail_regex FAIL_REGEX "command[ -]line option .* is valid for .* but not for Objective-C\\+\\+" # GNU
                         FAIL_REGEX "argument unused during compilation: .*") # Clang
  else()
    message (SEND_ERROR "check_compiler_flag: ${_lang}: unknown language.")
    return()
  endif()

  get_property (_supported_languages GLOBAL PROPERTY ENABLED_LANGUAGES)
  if (NOT _lang IN_LIST _supported_languages)
    message (SEND_ERROR "check_compiler_flag: ${_lang}: needs to be enabled before use.")
    return()
  endif()

  set(CMAKE_REQUIRED_DEFINITIONS ${_flag})

  # Normalize locale during test compilation.
  set(_locale_vars LC_ALL LC_MESSAGES LANG)
  foreach(v IN LISTS _locale_vars)
    set(_locale_vars_saved_${v} "$ENV{${v}}")
    set(ENV{${v}} C)
  endforeach()

  check_compiler_flag_common_patterns(_common_patterns)
  check_source_compiles(${_lang}
    "${_lang_src}"
    ${_var}
    ${_lang_fail_regex}
    ${_common_patterns}
    )

  foreach(v IN LISTS _locale_vars)
    set(ENV{${v}} ${_locale_vars_saved_${v}})
  endforeach()
  set(${_var} "${${_var}}" PARENT_SCOPE)
endfunction ()

cmake_policy(POP)