Modules/CheckLanguage.cmake

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

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

This module provides the ``check_language()`` macro to check whether a language
can be enabled using the :command:`enable_language` or :command:`project`
commands.

.. command:: check_language

  .. code-block:: cmake

    check_language(<lang>)

  This macro attempts to enable the language ``<lang>`` in a test project and
  records the results in the following cache variables:

  :variable:`CMAKE_<LANG>_COMPILER`
    If the language can be enabled, this variable is set to the compiler
    that was found.  If the language cannot be enabled, this variable is
    set to ``NOTFOUND``.

    If this variable is already set, either explicitly or cached by
    a previous call, the check is skipped.

  :variable:`CMAKE_<LANG>_HOST_COMPILER`
    This variable is set when ``<lang>`` is ``CUDA`` or ``HIP``.

    If the check detects an explicit host compiler that is required for
    compilation, this variable will be set to that compiler.
    If the check detects that no explicit host compiler is needed,
    this variable will be cleared.

    If this variable is already set, its value is preserved only if
    :variable:`CMAKE_<LANG>_COMPILER` is also set.
    Otherwise, the check runs and overwrites
    :variable:`CMAKE_<LANG>_HOST_COMPILER` with a new result.
    Note that :variable:`CMAKE_<LANG>_HOST_COMPILER` documents it should
    not be set without also setting
    :variable:`CMAKE_<LANG>_COMPILER` to a NVCC compiler.

  :variable:`CMAKE_<LANG>_PLATFORM <CMAKE_HIP_PLATFORM>`
    This variable is set to the detected GPU platform when ``<lang>`` is ``HIP``.

    If this variable is already set, its value is always preserved.  Only
    compatible values will be considered for :variable:`CMAKE_<LANG>_COMPILER`.

Examples
^^^^^^^^

This module is useful when a project does not always require a specific language
but may need to enable it for certain parts.  The following example checks for
the availability of the ``Fortran`` language and enables it if possible:

.. code-block:: cmake

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

include_guard(GLOBAL)

block(SCOPE_FOR POLICIES)
cmake_policy(SET CMP0126 NEW)

macro(check_language lang)
  if(NOT DEFINED CMAKE_${lang}_COMPILER)
    set(_desc "Looking for a ${lang} compiler")
    message(CHECK_START "${_desc}")
    file(REMOVE_RECURSE ${CMAKE_CURRENT_BINARY_DIR}/CMakeFiles/Check${lang})

    set(extra_compiler_variables)
    if("${lang}" MATCHES "^(CUDA|HIP)$" AND NOT CMAKE_GENERATOR MATCHES "Visual Studio")
      set(extra_compiler_variables "set(CMAKE_${lang}_HOST_COMPILER \\\"\${CMAKE_${lang}_HOST_COMPILER}\\\")")
    endif()

    if("${lang}" STREQUAL "HIP")
      list(APPEND extra_compiler_variables "set(CMAKE_${lang}_PLATFORM \\\"\${CMAKE_${lang}_PLATFORM}\\\")")
    endif()

    list(TRANSFORM extra_compiler_variables PREPEND "\"")
    list(TRANSFORM extra_compiler_variables APPEND "\\n\"")
    list(JOIN extra_compiler_variables "\n  " extra_compiler_variables)

    set(_cl_content
      "cmake_minimum_required(VERSION ${CMAKE_VERSION})
set(CMAKE_MODULE_PATH \"${CMAKE_MODULE_PATH}\")
project(Check${lang} ${lang})
file(WRITE \"\${CMAKE_CURRENT_BINARY_DIR}/result.cmake\"
  \"set(CMAKE_${lang}_COMPILER \\\"\${CMAKE_${lang}_COMPILER}\\\")\\n\"
  ${extra_compiler_variables}
  )"
    )

    file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/CMakeFiles/Check${lang}/CMakeLists.txt"
      "${_cl_content}")
    if(CMAKE_GENERATOR_INSTANCE)
      set(_D_CMAKE_GENERATOR_INSTANCE "-DCMAKE_GENERATOR_INSTANCE:INTERNAL=${CMAKE_GENERATOR_INSTANCE}")
    else()
      set(_D_CMAKE_GENERATOR_INSTANCE "")
    endif()
    if(CMAKE_GENERATOR MATCHES "^(Xcode$|Green Hills MULTI$|Visual Studio)")
      set(_D_CMAKE_MAKE_PROGRAM "")
    else()
      set(_D_CMAKE_MAKE_PROGRAM "-DCMAKE_MAKE_PROGRAM:FILEPATH=${CMAKE_MAKE_PROGRAM}")
    endif()
    if(CMAKE_TOOLCHAIN_FILE)
      set(_D_CMAKE_TOOLCHAIN_FILE "-DCMAKE_TOOLCHAIN_FILE:FILEPATH=${CMAKE_TOOLCHAIN_FILE}")
    else()
      set(_D_CMAKE_TOOLCHAIN_FILE "")
    endif()
    if(CMAKE_${lang}_PLATFORM)
      set(_D_CMAKE_LANG_PLATFORM "-DCMAKE_${lang}_PLATFORM:STRING=${CMAKE_${lang}_PLATFORM}")
    else()
      set(_D_CMAKE_LANG_PLATFORM "")
    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}
                                 ${_D_CMAKE_MAKE_PROGRAM}
                                 ${_D_CMAKE_TOOLCHAIN_FILE}
                                 ${_D_CMAKE_LANG_PLATFORM}
      OUTPUT_VARIABLE _cl_output
      ERROR_VARIABLE _cl_output
      RESULT_VARIABLE _cl_result
      )
    include(${CMAKE_CURRENT_BINARY_DIR}/CMakeFiles/Check${lang}/result.cmake OPTIONAL)
    if(CMAKE_${lang}_COMPILER AND "${_cl_result}" STREQUAL "0")
      message(CONFIGURE_LOG
        "${_desc} passed with the following output:\n"
        "${_cl_output}\n")
      set(_CHECK_COMPILER_STATUS CHECK_PASS)
    else()
      set(CMAKE_${lang}_COMPILER NOTFOUND)
      set(_CHECK_COMPILER_STATUS CHECK_FAIL)
      message(CONFIGURE_LOG
        "${_desc} failed with the following output:\n"
        "${_cl_output}\n")
    endif()
    message(${_CHECK_COMPILER_STATUS} "${CMAKE_${lang}_COMPILER}")
    set(CMAKE_${lang}_COMPILER "${CMAKE_${lang}_COMPILER}" CACHE FILEPATH "${lang} compiler")
    mark_as_advanced(CMAKE_${lang}_COMPILER)

    if(CMAKE_${lang}_HOST_COMPILER)
      message(STATUS "Looking for a ${lang} host compiler - ${CMAKE_${lang}_HOST_COMPILER}")
      set(CMAKE_${lang}_HOST_COMPILER "${CMAKE_${lang}_HOST_COMPILER}" CACHE FILEPATH "${lang} host compiler")
      mark_as_advanced(CMAKE_${lang}_HOST_COMPILER)
    endif()

    if(CMAKE_${lang}_PLATFORM)
      set(CMAKE_${lang}_PLATFORM "${CMAKE_${lang}_PLATFORM}" CACHE STRING "${lang} platform")
      mark_as_advanced(CMAKE_${lang}_PLATFORM)
    endif()
  endif()
endmacro()

endblock()