[lxc-devel] [lxc/master] autotools: fix check for -Wimplicit-fallthrough

[brauner on Github]

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From fd87516420653648c237d9b0a395ce1379c25e82 Mon Sep 17 00:00:00 2001
From: Christian Brauner <christian.brauner at ubuntu.com>
Date: Fri, 21 Sep 2018 23:07:09 +0200
Subject: [PATCH] autotools: fix check for -Wimplicit-fallthrough

Signed-off-by: Christian Brauner <christian.brauner at ubuntu.com>
---
 config/ax_check_compile_flag.m4 | 53 ---------------------------------
 configure.ac                    | 21 +++++++++++--
 2 files changed, 19 insertions(+), 55 deletions(-)
 delete mode 100644 config/ax_check_compile_flag.m4

diff --git a/config/ax_check_compile_flag.m4 b/config/ax_check_compile_flag.m4
deleted file mode 100644
index bd753b34d..000000000
--- a/config/ax_check_compile_flag.m4
+++ /dev/null
@@ -1,53 +0,0 @@
-# ===========================================================================
-#  https://www.gnu.org/software/autoconf-archive/ax_check_compile_flag.html
-# ===========================================================================
-#
-# SYNOPSIS
-#
-#   AX_CHECK_COMPILE_FLAG(FLAG, [ACTION-SUCCESS], [ACTION-FAILURE], [EXTRA-FLAGS], [INPUT])
-#
-# DESCRIPTION
-#
-#   Check whether the given FLAG works with the current language's compiler
-#   or gives an error.  (Warnings, however, are ignored)
-#
-#   ACTION-SUCCESS/ACTION-FAILURE are shell commands to execute on
-#   success/failure.
-#
-#   If EXTRA-FLAGS is defined, it is added to the current language's default
-#   flags (e.g. CFLAGS) when the check is done.  The check is thus made with
-#   the flags: "CFLAGS EXTRA-FLAGS FLAG".  This can for example be used to
-#   force the compiler to issue an error when a bad flag is given.
-#
-#   INPUT gives an alternative input source to AC_COMPILE_IFELSE.
-#
-#   NOTE: Implementation based on AX_CFLAGS_GCC_OPTION. Please keep this
-#   macro in sync with AX_CHECK_{PREPROC,LINK}_FLAG.
-#
-# LICENSE
-#
-#   Copyright (c) 2008 Guido U. Draheim <guidod at gmx.de>
-#   Copyright (c) 2011 Maarten Bosmans <mkbosmans at gmail.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 6
-
-AC_DEFUN([AX_CHECK_COMPILE_FLAG],
-[AC_PREREQ(2.64)dnl for _AC_LANG_PREFIX and AS_VAR_IF
-AS_VAR_PUSHDEF([CACHEVAR],[ax_cv_check_[]_AC_LANG_ABBREV[]flags_$4_$1])dnl
-AC_CACHE_CHECK([whether _AC_LANG compiler accepts $1], CACHEVAR, [
-  ax_check_save_flags=$[]_AC_LANG_PREFIX[]FLAGS
-  _AC_LANG_PREFIX[]FLAGS="$[]_AC_LANG_PREFIX[]FLAGS $4 $1"
-  AC_COMPILE_IFELSE([m4_default([$5],[AC_LANG_PROGRAM()])],
-    [AS_VAR_SET(CACHEVAR,[yes])],
-    [AS_VAR_SET(CACHEVAR,[no])])
-  _AC_LANG_PREFIX[]FLAGS=$ax_check_save_flags])
-AS_VAR_IF(CACHEVAR,yes,
-  [m4_default([$2], :)],
-  [m4_default([$3], :)])
-AS_VAR_POPDEF([CACHEVAR])dnl
-])dnl AX_CHECK_COMPILE_FLAGS
diff --git a/configure.ac b/configure.ac
index 24c53ca0c..ecc45369e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -683,8 +683,25 @@ AC_PROG_SED
 # See if we support thread-local storage.
 LXC_CHECK_TLS
 
-AX_CHECK_COMPILE_FLAG([-fdiagnostics-color], [CFLAGS="$CFLAGS -fdiagnostics-color"],,[-Werror])
-AX_CHECK_COMPILE_FLAG([-fdiagnostics-color], [CFLAGS="$CFLAGS -Wimplicit-fallthrough"],,[-Werror])
+AC_MSG_CHECKING(for -Wimplicit-fallthrough)
+OLD_CFLAGS="$CFLAGS"
+OLD_CPPFLAGS="$CPPFLAGS"
+CFLAGS="-Wimplicit-fallthrough -Werror"
+CPPFLAGS="-Wimplicit-fallthrough -Werror"
+AC_LINK_IFELSE([
+  AC_LANG_SOURCE(
+    [[int main() { return 0; }]]
+  )],[have_implicit_fallthrough=yes],[have_implicit_fallthrough=no])
+AM_CONDITIONAL([HAVE_IMPLICIT_FALLTHROUGH], [test "x$have_implicit_fallthrough" = "xyes"])
+if test "x$have_implicit_fallthrough" = "xyes"; then
+	CPPFLAGS="$OLD_CPPFLAGS $CPPFLAGS"
+	CFLAGS="$OLD_CFLAGS $CFLAGS"
+	AC_MSG_RESULT([yes])
+else
+	CPPFLAGS="$OLD_CPPFLAGS"
+	CFLAGS="$OLD_CFLAGS"
+	AC_MSG_RESULT([no])
+fi
 
 CFLAGS="$CFLAGS -Wvla -std=gnu11"
 if test "x$enable_werror" = "xyes"; then