From: Paul Eggert <eggert@cs.ucla.edu>
Date: Thu, 28 Nov 2013 08:46:06 +0000 (-0800)
Subject: ignore-value: revert previous code change
X-Git-Tag: snapshot-start~28
X-Git-Url: http://erislabs.net/gitweb/?p=gnulib.git;a=commitdiff_plain;h=37f8a6b207bc71cbfffd4c53ebf4e20955e0776b

ignore-value: revert previous code change

* lib/ignore-value.h (ignore_value): Use __extension__ and
__typeof__ only for GCC 3.4 and later.  Reported by Eric Blake in
<http://lists.gnu.org/archive/html/bug-gnulib/2013-11/msg00102.html>.
Change the comment to try to explain this better.
---

diff --git a/ChangeLog b/ChangeLog
index 61b5f40fc..21659eafe 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2013-11-28  Paul Eggert  <eggert@cs.ucla.edu>
+
+	ignore-value: revert previous code change
+	* lib/ignore-value.h (ignore_value): Use __extension__ and
+	__typeof__ only for GCC 3.4 and later.  Reported by Eric Blake in
+	<http://lists.gnu.org/archive/html/bug-gnulib/2013-11/msg00102.html>.
+	Change the comment to try to explain this better.
+
 2013-11-27  Pádraig Brady <P@draigBrady.com>
 
 	selinux-h: improve stub types and add more stub functions
diff --git a/lib/ignore-value.h b/lib/ignore-value.h
index f079a0629..633c44adc 100644
--- a/lib/ignore-value.h
+++ b/lib/ignore-value.h
@@ -35,10 +35,12 @@
 #ifndef _GL_IGNORE_VALUE_H
 #define _GL_IGNORE_VALUE_H
 
-/* The __attribute__((__warn_unused_result__)) feature is available in
-   gcc versions 3.4 and newer, while __typeof__ and __extension__ have
-   been available since 2.0 at least.  */
-#if 2 <= __GNUC__
+/* Normally casting an expression to void discards its value, but GCC
+   versions 3.4 and newer have __attribute__ ((__warn_unused_result__))
+   which may cause unwanted diagnostics in that case.  Use __typeof__
+   and __extension__ to work around the problem, if the workaround is
+   known to be needed.  */
+#if 3 < __GNUC__ + (4 <= __GNUC_MINOR__)
 # define ignore_value(x) \
     (__extension__ ({ __typeof__ (x) __x = (x); (void) __x; }))
 #else