CMake/Modules/CheckLanguage.cmake

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

#[=======================================================================[.rst:
CheckLanguage
-------------

Check if a language can be enabled

Usage:

::

  check_language(<lang>)

where ``<lang>`` is a language that may be passed to :command:`enable_language`
such as ``Fortran``.  If :variable:`CMAKE_<LANG>_COMPILER` is already defined
the check does nothing.  Otherwise it tries enabling the language in a
test project.  The result is cached in :variable:`CMAKE_<LANG>_COMPILER`
as the compiler that was found, or ``NOTFOUND`` if the language cannot be
enabled.

Example:

::

  check_language(Fortran)
  if(CMAKE_Fortran_COMPILER)
    enable_language(Fortran)
  else()
    message(STATUS "No Fortran support")
  endif()
#]=======================================================================]

include_guard(GLOBAL)

macro(check_language lang)
  if(NOT DEFINED CMAKE_${lang}_COMPILER)
    set(_desc "Looking for a ${lang} compiler")
    message(STATUS ${_desc})
    file(REMOVE_RECURSE ${CMAKE_CURRENT_BINARY_DIR}/CMakeFiles/Check${lang})
    file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/CMakeFiles/Check${lang}/CMakeLists.txt"
      "cmake_minimum_required(VERSION ${CMAKE_VERSION})
project(Check${lang} ${lang})
file(WRITE \"\${CMAKE_CURRENT_BINARY_DIR}/result.cmake\"
  \"set(CMAKE_${lang}_COMPILER \\\"\${CMAKE_${lang}_COMPILER}\\\")\\n\"
  )
")
    if(CMAKE_GENERATOR_INSTANCE)
      set(_D_CMAKE_GENERATOR_INSTANCE "-DCMAKE_GENERATOR_INSTANCE:INTERNAL=${CMAKE_GENERATOR_INSTANCE}")
    else()
      set(_D_CMAKE_GENERATOR_INSTANCE "")
    endif()
    execute_process(
      WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/CMakeFiles/Check${lang}
      COMMAND ${CMAKE_COMMAND} . -G ${CMAKE_GENERATOR}
                                 -A "${CMAKE_GENERATOR_PLATFORM}"
                                 -T "${CMAKE_GENERATOR_TOOLSET}"
                                 ${_D_CMAKE_GENERATOR_INSTANCE}
      OUTPUT_VARIABLE output
      ERROR_VARIABLE output
      RESULT_VARIABLE result
      )
    include(${CMAKE_CURRENT_BINARY_DIR}/CMakeFiles/Check${lang}/result.cmake OPTIONAL)
    if(CMAKE_${lang}_COMPILER AND "${result}" STREQUAL "0")
      file(APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeOutput.log
        "${_desc} passed with the following output:\n"
        "${output}\n")
    else()
      set(CMAKE_${lang}_COMPILER NOTFOUND)
      file(APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeError.log
        "${_desc} failed with the following output:\n"
        "${output}\n")
    endif()
    message(STATUS "${_desc} - ${CMAKE_${lang}_COMPILER}")
    set(CMAKE_${lang}_COMPILER "${CMAKE_${lang}_COMPILER}" CACHE FILEPATH "${lang} compiler")
    mark_as_advanced(CMAKE_${lang}_COMPILER)
  endif()
endmacro()