[libvirt] [PATCH 4/6] Correctly detect warning flags with clang

[Paul Eggert]

On 05/13/2013 12:28 PM, Eric Blake wrote:
> Some of this needs to be imported into upstream gnulib.

I gave it a try, by installing the following.
I'll follow up on bug-gnulib with 7 other clang-related patches.

>From 45fc031e607cb82dce777228d9334cdac16ca648 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert at cs.ucla.edu>
Date: Wed, 15 May 2013 00:07:15 -0700
Subject: [PATCH 1/8] warnings: port to clang

Problem reported by Daniel P. Berrange via Eric Blake in
<http://lists.gnu.org/archive/html/bug-gnulib/2013-05/msg00055.html>.
* m4/warnings.m4 (gl_UNKNOWN_WARNINGS_ARE_ERRORS): New macro.
(gl_WARN_ADD): Use it.
---
 ChangeLog      |  8 ++++++++
 m4/warnings.m4 | 15 ++++++++++++---
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 08f2fe0..b7aceaa 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2013-05-15  Paul Eggert  <eggert at cs.ucla.edu>
+
+	warnings: port to clang
+	Problem reported by Daniel P. Berrange via Eric Blake in
+	<http://lists.gnu.org/archive/html/bug-gnulib/2013-05/msg00055.html>.
+	* m4/warnings.m4 (gl_UNKNOWN_WARNINGS_ARE_ERRORS): New macro.
+	(gl_WARN_ADD): Use it.
+
 2013-05-11  Jim Meyering  <meyering at fb.com>
 
 	quotearg: do not read beyond end of buffer
diff --git a/m4/warnings.m4 b/m4/warnings.m4
index 4b2ac38..1848732 100644
--- a/m4/warnings.m4
+++ b/m4/warnings.m4
@@ -1,4 +1,4 @@
-# warnings.m4 serial 7
+# warnings.m4 serial 8
 dnl Copyright (C) 2008-2013 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -27,7 +27,7 @@ AC_DEFUN([gl_COMPILER_OPTION_IF],
 AS_VAR_PUSHDEF([gl_Flags], [_AC_LANG_PREFIX[]FLAGS])dnl
 AC_CACHE_CHECK([whether _AC_LANG compiler handles $1], m4_defn([gl_Warn]), [
   gl_save_compiler_FLAGS="$gl_Flags"
-  gl_AS_VAR_APPEND(m4_defn([gl_Flags]), [" $1"])
+  gl_AS_VAR_APPEND(m4_defn([gl_Flags]), [" $gl_unknown_warnings_are_errors $1"])
   AC_COMPILE_IFELSE([m4_default([$4], [AC_LANG_PROGRAM([])])],
                     [AS_VAR_SET(gl_Warn, [yes])],
                     [AS_VAR_SET(gl_Warn, [no])])
@@ -38,6 +38,14 @@ AS_VAR_POPDEF([gl_Flags])dnl
 AS_VAR_POPDEF([gl_Warn])dnl
 ])
 
+# gl_UNKNOWN_WARNINGS_ARE_ERRORS
+# ------------------------------
+# Clang doesn't complain about unknown warning options unless one also
+# specifies -Wunknown-warning-option -Werror.  Detect this.
+AC_DEFUN([gl_UNKNOWN_WARNINGS_ARE_ERRORS],
+[gl_COMPILER_OPTION_IF([-Werror -Wunknown-warning-option],
+   [gl_unknown_warnings_are_errors='-Wunknown-warning-option -Werror'],
+   [gl_unknown_warnings_are_errors=])])
 
 # gl_WARN_ADD(OPTION, [VARIABLE = WARN_CFLAGS],
 #             [PROGRAM = AC_LANG_PROGRAM()])
@@ -47,7 +55,8 @@ AS_VAR_POPDEF([gl_Warn])dnl
 #
 # If VARIABLE is a variable name, AC_SUBST it.
 AC_DEFUN([gl_WARN_ADD],
-[gl_COMPILER_OPTION_IF([$1],
+[AC_REQUIRE([gl_UNKNOWN_WARNINGS_ARE_ERRORS])
+gl_COMPILER_OPTION_IF([$1],
   [gl_AS_VAR_APPEND(m4_if([$2], [], [[WARN_CFLAGS]], [[$2]]), [" $1"])],
   [],
   [$3])
-- 
1.7.11.7