#

# SYNOPSIS

#

#   DLP_FALLTHROUGH

#

# DESCRIPTION

#

#   This macro checks if the compiler supports a fallthrough warning

#   suppression attribute in GCC or CLANG style.

#

#   If a fallthrough warning suppression attribute is supported define

#   HAVE_<STYLE>_ATTRIBUTE_FALLTHROUGH.

#

#   The macro caches its result in ax_cv_have_<style>_attribute_fallthrough

#   variables.

#

# LICENSE

#

#   Copyright (c) 2017 David Tardon <dtardon@redhat.com>

#

#   Copying and distribution of this file, with or without modification, are

#   permitted in any medium without royalty provided the copyright notice

#   and this notice are preserved.  This file is offered as-is, without any

#   warranty.

#serial 1

m4_defun([_DLP_FALLTHROUGH], [

    AS_VAR_PUSHDEF([ac_var], [ax_cv_have_$2_attribute_falltrough])

    AC_CACHE_CHECK([for $1], [ac_var], [

        AC_LINK_IFELSE([AC_LANG_PROGRAM([

                void foo(int &i)

                {

                    switch (i)

                    {

                        case 0:

                            i += 1;

                            $1;

                        default:

                            i += 1;

                    }

                }

            ], [])

            ],

            dnl GCC doesn't exit with an error if an unknown attribute is

            dnl provided but only outputs a warning, so accept the attribute

            dnl only if no warning were issued.

            [AS_IF([test -s conftest.err],

                [AS_VAR_SET([ac_var], [no])],

                [AS_VAR_SET([ac_var], [yes])])],

            [AS_VAR_SET([ac_var], [no])])

    ])

    AS_IF([test yes = AS_VAR_GET([ac_var])],

        [AC_DEFINE_UNQUOTED(AS_TR_CPP(HAVE_$3_ATTRIBUTE_FALLTHROUGH), 1,

            [Define to 1 if the system has the $4-style `fallthrough' attribute])], [])

    AS_VAR_POPDEF([ac_var])

])

AC_DEFUN([DLP_FALLTHROUGH], [

    _DLP_FALLTHROUGH([[__attribute__((fallthrough))]], [gcc], [GCC], [GNU])

    _DLP_FALLTHROUGH([[[[clang:fallthrough]]]], [clang], [CLANG], [clang])

])