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# 00gnulib.m4 serial 8
dnl Copyright (C) 2009-2020 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
dnl with or without modifications, as long as this notice is preserved.
dnl This file must be named something that sorts before all other
dnl gnulib-provided .m4 files. It is needed until the clang fix has
dnl been included in Autoconf.
# The following definitions arrange to use a compiler option
# -Werror=implicit-function-declaration in AC_CHECK_DECL, when the
# compiler is clang. Without it, clang implicitly declares "known"
# library functions in C mode, but not in C++ mode, which would cause
# Gnulib to omit a declaration and thus later produce an error in C++
# mode. As of clang 9.0, these "known" functions are identified through
# LIBBUILTIN invocations in the LLVM source file
# llvm/tools/clang/include/clang/Basic/Builtins.def.
# It's not possible to AC_REQUIRE the extra tests from AC_CHECK_DECL,
# because AC_CHECK_DECL, like other Autoconf built-ins, is not supposed
# to AC_REQUIRE anything: some configure.ac files have their first
# AC_CHECK_DECL executed conditionally. Therefore append the extra tests
# to AC_PROG_CC.
AC_DEFUN([gl_COMPILER_CLANG],
[
dnl AC_REQUIRE([AC_PROG_CC])
AC_CACHE_CHECK([whether the compiler is clang],
[gl_cv_compiler_clang],
[dnl Use _AC_COMPILE_IFELSE instead of AC_EGREP_CPP, to avoid error
dnl "circular dependency of AC_LANG_COMPILER(C)" if AC_PROG_CC has
dnl not yet been invoked.
_AC_COMPILE_IFELSE(
[AC_LANG_PROGRAM([[
#ifdef __clang__
barfbarf
#endif
]],[[]])
],
[gl_cv_compiler_clang=no],
[gl_cv_compiler_clang=yes])
])
])
AC_DEFUN([gl_COMPILER_PREPARE_CHECK_DECL],
[
dnl AC_REQUIRE([AC_PROG_CC])
dnl AC_REQUIRE([gl_COMPILER_CLANG])
AC_CACHE_CHECK([for compiler option needed when checking for declarations],
[gl_cv_compiler_check_decl_option],
[if test $gl_cv_compiler_clang = yes; then
dnl Test whether the compiler supports the option
dnl '-Werror=implicit-function-declaration'.
save_ac_compile="$ac_compile"
ac_compile="$ac_compile -Werror=implicit-function-declaration"
dnl Use _AC_COMPILE_IFELSE instead of AC_COMPILE_IFELSE, to avoid a
dnl warning "AC_COMPILE_IFELSE was called before AC_USE_SYSTEM_EXTENSIONS".
_AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[]],[[]])],
[gl_cv_compiler_check_decl_option='-Werror=implicit-function-declaration'],
[gl_cv_compiler_check_decl_option=none])
ac_compile="$save_ac_compile"
else
gl_cv_compiler_check_decl_option=none
fi
])
if test "x$gl_cv_compiler_check_decl_option" != xnone; then
ac_compile_for_check_decl="$ac_compile $gl_cv_compiler_check_decl_option"
else
ac_compile_for_check_decl="$ac_compile"
fi
])
dnl Redefine _AC_CHECK_DECL_BODY so that it references ac_compile_for_check_decl
dnl instead of ac_compile. If, for whatever reason, the override of AC_PROG_CC
dnl in zzgnulib.m4 is inactive, use the original ac_compile.
m4_define([_AC_CHECK_DECL_BODY],
[ ac_save_ac_compile="$ac_compile"
if test -n "$ac_compile_for_check_decl"; then
ac_compile="$ac_compile_for_check_decl"
fi]
m4_defn([_AC_CHECK_DECL_BODY])[ ac_compile="$ac_save_ac_compile"
])
# gl_00GNULIB
# -----------
# Witness macro that this file has been included. Needed to force
# Automake to include this file prior to all other gnulib .m4 files.
AC_DEFUN([gl_00GNULIB])

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