Re: [PATCH] lib/rename.c: Conditionally define the out label

[Pádraig Brady]

On 06/01/2014 09:59 PM, Pádraig Brady wrote:
> On 06/01/2014 09:34 AM, Ben Walton wrote:
>>   * Avoid possible compiler warnings/errors by defining the out label
>>     only when it may be accessed.
>>
>> Signed-off-by: Ben Walton <address@hidden>
>> ---
>>
>> Hi All,
>>
>> When building coreutils 8.22 on Solaris with -Werror=unused-label, the build
>> fails with:
>>
>> lib/rename.c: In function 'rpl_rename':
>> lib/rename.c:465:2: error: label 'out' defined but not used 
>> [-Werror=unused-label]
>>   out:
>>   ^
> 
> Are you building from a git checkout repo?
> Otherwise you should have to configure --enable-gcc-warnings
> to get -Werror enabled?
> 
>> I think this should make the compiler happier. Feel free to suggest better
>> solutions though. I'm not sure this is the best way to handle it.
>>
>>  lib/rename.c | 7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/lib/rename.c b/lib/rename.c
>> index 2116028..9c507c2 100644
>> --- a/lib/rename.c
>> +++ b/lib/rename.c
>> @@ -462,7 +462,14 @@ rpl_rename (char const *src, char const *dst)
>>  
>>    ret_val = rename (src_temp, dst_temp);
>>    rename_errno = errno;
>> +
>> +# if (RENAME_TRAILING_SLASH_SOURCE_BUG || RENAME_DEST_EXISTS_BUG        \
>> +      || RENAME_HARD_LINK_BUG)
>> +  /* Avoid compiler warnings about unused labels. Only
>> +     create this label if it will be used. */
>>   out:
>> +# endif
>> +
> 
> Note one can mark a label as possibly unused like:
> 
>   out: _GL_UNUSED;
> 
> That's supported on all gcc, and newer g++ since
> https://gcc.gnu.org/ml/gcc-patches/2009-05/msg01897.html
> So to support compiling with older g++ one could:
> 
>   out:
> #if (!defined __cplusplus) || __GNUC__ >=  ?
>     || (__GNUC__ == ? && __GNUC_MINOR__ >= ?)
>  _GL_UNUSED;
> #endif
> 
> With the ?s filled in as appropriate.

Actually the above should be abstracted away from rename.c,
So you can instead do:

   out: _GL_UNUSED_LABEL

I'll apply the following to gnulib-common.m4 to support that:

+/* gcc supports the "unused" attribute on possibly unused labels, and
+   g++ has since version 4.5.  */
+#if !defined __cplusplus || __GNUC__ > 4 \
+    || (__GNUC__ == 4 && __GNUC_MINOR__ >= 5)
+# define _GL_UNUSED_LABEL _GL_UNUSED;
+#else
+# define _GL_UNUSED_LABEL
+#endif

thanks,
Pádraig.