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check_decls.m4
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# config/check_decls.m4
# This file redefines the standard Autoconf macro _AC_CHECK_DECL_BODY,
# and adds a supporting function _AC_UNDECLARED_WARNING, to make
# AC_CHECK_DECLS behave correctly when checking for built-in library
# functions with clang.
# This is based on commit 82ef7805faffa151e724aa76c245ec590d174580
# in the Autoconf git repository. We can drop it if they ever get
# around to releasing a new version of Autoconf. In the meantime,
# it's distributed under Autoconf's license:
# This file is part of Autoconf. This program is free
# software; you can redistribute it and/or modify it under the
# terms of the GNU General Public License as published by the
# Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# Under Section 7 of GPL version 3, you are granted additional
# permissions described in the Autoconf Configure Script Exception,
# version 3.0, as published by the Free Software Foundation.
#
# You should have received a copy of the GNU General Public License
# and a copy of the Autoconf Configure Script Exception along with
# this program; see the files COPYINGv3 and COPYING.EXCEPTION
# respectively. If not, see <http://www.gnu.org/licenses/>.
# Written by David MacKenzie, with help from
# Franc,ois Pinard, Karl Berry, Richard Pixley, Ian Lance Taylor,
# Roland McGrath, Noah Friedman, david d zuhn, and many others.
# _AC_UNDECLARED_WARNING
# ----------------------
# Set ac_[]_AC_LANG_ABBREV[]_decl_warn_flag=yes if the compiler uses a warning,
# not a more-customary error, to report some undeclared identifiers. Fail when
# an affected compiler warns also on valid input. _AC_PROG_PREPROC_WORKS_IFELSE
# solves a related problem.
AC_DEFUN([_AC_UNDECLARED_WARNING],
[# The Clang compiler raises a warning for an undeclared identifier that matches
# a compiler builtin function. All extant Clang versions are affected, as of
# Clang 3.6.0. Test a builtin known to every version. This problem affects the
# C and Objective C languages, but Clang does report an error under C++ and
# Objective C++.
#
# Passing -fno-builtin to the compiler would suppress this problem. That
# strategy would have the advantage of being insensitive to stray warnings, but
# it would make tests less realistic.
AC_CACHE_CHECK([how $[]_AC_CC[] reports undeclared, standard C functions],
[ac_cv_[]_AC_LANG_ABBREV[]_decl_report],
[AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [(void) strchr;])],
[AS_IF([test -s conftest.err], [dnl
# For AC_CHECK_DECL to react to warnings, the compiler must be silent on
# valid AC_CHECK_DECL input. No library function is consistently available
# on freestanding implementations, so test against a dummy declaration.
# Include always-available headers on the off chance that they somehow
# elicit warnings.
AC_COMPILE_IFELSE([AC_LANG_PROGRAM([dnl
#include <float.h>
#include <limits.h>
#include <stdarg.h>
#include <stddef.h>
extern void ac_decl (int, char *);],
[@%:@ifdef __cplusplus
(void) ac_decl ((int) 0, (char *) 0);
(void) ac_decl;
@%:@else
(void) ac_decl;
@%:@endif
])],
[AS_IF([test -s conftest.err],
[AC_MSG_FAILURE([cannot detect from compiler exit status or warnings])],
[ac_cv_[]_AC_LANG_ABBREV[]_decl_report=warning])],
[AC_MSG_FAILURE([cannot compile a simple declaration test])])],
[AC_MSG_FAILURE([compiler does not report undeclared identifiers])])],
[ac_cv_[]_AC_LANG_ABBREV[]_decl_report=error])])
case $ac_cv_[]_AC_LANG_ABBREV[]_decl_report in
warning) ac_[]_AC_LANG_ABBREV[]_decl_warn_flag=yes ;;
*) ac_[]_AC_LANG_ABBREV[]_decl_warn_flag= ;;
esac
])# _AC_UNDECLARED_WARNING
# _AC_CHECK_DECL_BODY
# -------------------
# Shell function body for AC_CHECK_DECL.
m4_define([_AC_CHECK_DECL_BODY],
[ AS_LINENO_PUSH([$[]1])
# Initialize each $ac_[]_AC_LANG_ABBREV[]_decl_warn_flag once.
AC_DEFUN([_AC_UNDECLARED_WARNING_]_AC_LANG_ABBREV,
[_AC_UNDECLARED_WARNING])dnl
AC_REQUIRE([_AC_UNDECLARED_WARNING_]_AC_LANG_ABBREV)dnl
[as_decl_name=`echo $][2|sed 's/ *(.*//'`]
[as_decl_use=`echo $][2|sed -e 's/(/((/' -e 's/)/) 0&/' -e 's/,/) 0& (/g'`]
AC_CACHE_CHECK([whether $as_decl_name is declared], [$[]3],
[ac_save_werror_flag=$ac_[]_AC_LANG_ABBREV[]_werror_flag
ac_[]_AC_LANG_ABBREV[]_werror_flag="$ac_[]_AC_LANG_ABBREV[]_decl_warn_flag$ac_[]_AC_LANG_ABBREV[]_werror_flag"
AC_COMPILE_IFELSE([AC_LANG_PROGRAM([$[]4],
[@%:@ifndef $[]as_decl_name
@%:@ifdef __cplusplus
(void) $[]as_decl_use;
@%:@else
(void) $[]as_decl_name;
@%:@endif
@%:@endif
])],
[AS_VAR_SET([$[]3], [yes])],
[AS_VAR_SET([$[]3], [no])])
ac_[]_AC_LANG_ABBREV[]_werror_flag=$ac_save_werror_flag])
AS_LINENO_POP
])# _AC_CHECK_DECL_BODY