Re: [PATCH] ignore-value: prefer GCC version back through 2.0

[Paul Eggert]

Thanks for explaining.  I see that I completely missed the point.
I changed the code back, and redid the comment in an attempt to
try to explain things, as follows:
---
 ChangeLog          |  8 ++++++++
 lib/ignore-value.h | 10 ++++++----
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 61b5f40..21659ea 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2013-11-28  Paul Eggert  <address@hidden>
+
+       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 <address@hidden>
 
        selinux-h: improve stub types and add more stub functions
diff --git a/lib/ignore-value.h b/lib/ignore-value.h
index f079a06..633c44a 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
-- 
1.8.3.1