1# Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
2# file Copyright.txt or https://cmake.org/licensing for details.
3
4#[=======================================================================[.rst:
5CheckLinkerFlag
6---------------
7
8.. versionadded:: 3.18
9
10Check whether the compiler supports a given link flag.
11
12.. command:: check_linker_flag
13
14  .. code-block:: cmake
15
16    check_linker_flag(<lang> <flag> <var>)
17
18Check that the link ``<flag>`` is accepted by the ``<lang>`` compiler without
19a diagnostic.  Stores the result in an internal cache entry named ``<var>``.
20
21This command temporarily sets the ``CMAKE_REQUIRED_LINK_OPTIONS`` variable
22and calls the :command:`check_source_compiles` command from the
23:module:`CheckSourceCompiles` module.  See that module's documentation
24for a listing of variables that can otherwise modify the build.
25
26The underlying implementation relies on the :prop_tgt:`LINK_OPTIONS` property
27to check the specified flag. The ``LINKER:`` prefix, as described in the
28:command:`target_link_options` command, can be used as well.
29
30A positive result from this check indicates only that the compiler did not
31issue a diagnostic message when given the link flag.  Whether the flag has any
32effect or even a specific one is beyond the scope of this module.
33
34.. note::
35  Since the :command:`try_compile` command forwards flags from variables
36  like :variable:`CMAKE_<LANG>_FLAGS`, unknown flags in such variables may
37  cause a false negative for this check.
38#]=======================================================================]
39
40include_guard(GLOBAL)
41
42include(CMakeCheckCompilerFlagCommonPatterns)
43
44cmake_policy(PUSH)
45cmake_policy(SET CMP0054 NEW) # if() quoted variables not dereferenced
46cmake_policy(SET CMP0057 NEW) # if() supports IN_LIST
47
48function(CHECK_LINKER_FLAG _lang _flag _var)
49  get_property (_supported_languages GLOBAL PROPERTY ENABLED_LANGUAGES)
50  if (NOT _lang IN_LIST _supported_languages)
51    message (SEND_ERROR "check_linker_flag: ${_lang}: unknown language.")
52    return()
53  endif()
54
55  include (CheckSourceCompiles)
56
57  set(CMAKE_REQUIRED_LINK_OPTIONS "${_flag}")
58
59  # Normalize locale during test compilation.
60  set(_locale_vars LC_ALL LC_MESSAGES LANG)
61  foreach(v IN LISTS _locale_vars)
62    set(_locale_vars_saved_${v} "$ENV{${v}}")
63    set(ENV{${v}} C)
64  endforeach()
65
66  if (_lang MATCHES "^(C|CXX)$")
67    set (_source "int main() { return 0; }")
68  elseif (_lang STREQUAL "Fortran")
69    set (_source "       program test\n       stop\n       end program")
70  elseif (_lang MATCHES "CUDA")
71    set (_source "__host__ int main() { return 0; }")
72  elseif (_lang MATCHES "HIP")
73    set (_source "__host__ int main() { return 0; }")
74  elseif (_lang MATCHES "^(OBJC|OBJCXX)$")
75    set (_source "#ifndef __OBJC__\n#  error \"Not an Objective-C++ compiler\"\n#endif\nint main(void) { return 0; }")
76  else()
77    message (SEND_ERROR "check_linker_flag: ${_lang}: unsupported language.")
78    return()
79  endif()
80  check_compiler_flag_common_patterns(_common_patterns)
81
82  check_source_compiles(${_lang} "${_source}" ${_var} ${_common_patterns})
83
84  foreach(v IN LISTS _locale_vars)
85    set(ENV{${v}} ${_locale_vars_saved_${v}})
86  endforeach()
87  set(${_var} "${${_var}}" PARENT_SCOPE)
88endfunction()
89
90cmake_policy(POP)
91