gnulib/import/m4/00gnulib.m4

   1 # 00gnulib.m4 serial 8
   2 dnl Copyright (C) 2009-2021 Free Software Foundation, Inc.
   3 dnl This file is free software; the Free Software Foundation
   4 dnl gives unlimited permission to copy and/or distribute it,
   5 dnl with or without modifications, as long as this notice is preserved.
   6
   7 dnl This file must be named something that sorts before all other
   8 dnl gnulib-provided .m4 files.  It is needed until the clang fix has
   9 dnl been included in Autoconf.
  10
  11 # The following definitions arrange to use a compiler option
  12 # -Werror=implicit-function-declaration in AC_CHECK_DECL, when the
  13 # compiler is clang.  Without it, clang implicitly declares "known"
  14 # library functions in C mode, but not in C++ mode, which would cause
  15 # Gnulib to omit a declaration and thus later produce an error in C++
  16 # mode.  As of clang 9.0, these "known" functions are identified through
  17 # LIBBUILTIN invocations in the LLVM source file
  18 # llvm/tools/clang/include/clang/Basic/Builtins.def.
  19 # It's not possible to AC_REQUIRE the extra tests from AC_CHECK_DECL,
  20 # because AC_CHECK_DECL, like other Autoconf built-ins, is not supposed
  21 # to AC_REQUIRE anything: some configure.ac files have their first
  22 # AC_CHECK_DECL executed conditionally.  Therefore append the extra tests
  23 # to AC_PROG_CC.
  24 AC_DEFUN([gl_COMPILER_CLANG],
  25 [
  26 dnl AC_REQUIRE([AC_PROG_CC])
  27   AC_CACHE_CHECK([whether the compiler is clang],
  28     [gl_cv_compiler_clang],
  29     [dnl Use _AC_COMPILE_IFELSE instead of AC_EGREP_CPP, to avoid error
  30      dnl "circular dependency of AC_LANG_COMPILER(C)" if AC_PROG_CC has
  31      dnl not yet been invoked.
  32      _AC_COMPILE_IFELSE(
  33         [AC_LANG_PROGRAM([[
  34            #ifdef __clang__
  35            barfbarf
  36            #endif
  37            ]],[[]])
  38         ],
  39         [gl_cv_compiler_clang=no],
  40         [gl_cv_compiler_clang=yes])
  41     ])
  42 ])
  43 AC_DEFUN([gl_COMPILER_PREPARE_CHECK_DECL],
  44 [
  45 dnl AC_REQUIRE([AC_PROG_CC])
  46 dnl AC_REQUIRE([gl_COMPILER_CLANG])
  47   AC_CACHE_CHECK([for compiler option needed when checking for declarations],
  48     [gl_cv_compiler_check_decl_option],
  49     [if test $gl_cv_compiler_clang = yes; then
  50        dnl Test whether the compiler supports the option
  51        dnl '-Werror=implicit-function-declaration'.
  52        save_ac_compile="$ac_compile"
  53        ac_compile="$ac_compile -Werror=implicit-function-declaration"
  54        dnl Use _AC_COMPILE_IFELSE instead of AC_COMPILE_IFELSE, to avoid a
  55        dnl warning "AC_COMPILE_IFELSE was called before AC_USE_SYSTEM_EXTENSIONS".
  56        _AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[]],[[]])],
  57          [gl_cv_compiler_check_decl_option='-Werror=implicit-function-declaration'],
  58          [gl_cv_compiler_check_decl_option=none])
  59        ac_compile="$save_ac_compile"
  60      else
  61        gl_cv_compiler_check_decl_option=none
  62      fi
  63     ])
  64   if test "x$gl_cv_compiler_check_decl_option" != xnone; then
  65     ac_compile_for_check_decl="$ac_compile $gl_cv_compiler_check_decl_option"
  66   else
  67     ac_compile_for_check_decl="$ac_compile"
  68   fi
  69 ])
  70 dnl Redefine _AC_CHECK_DECL_BODY so that it references ac_compile_for_check_decl
  71 dnl instead of ac_compile.  If, for whatever reason, the override of AC_PROG_CC
  72 dnl in zzgnulib.m4 is inactive, use the original ac_compile.
  73 m4_define([_AC_CHECK_DECL_BODY],
  74 [  ac_save_ac_compile="$ac_compile"
  75   if test -n "$ac_compile_for_check_decl"; then
  76     ac_compile="$ac_compile_for_check_decl"
  77   fi]
  78 m4_defn([_AC_CHECK_DECL_BODY])[  ac_compile="$ac_save_ac_compile"
  79 ])
  80
  81 # gl_00GNULIB
  82 # -----------
  83 # Witness macro that this file has been included.  Needed to force
  84 # Automake to include this file prior to all other gnulib .m4 files.
  85 AC_DEFUN([gl_00GNULIB])