Re: failure to build due to ignoring fwrite() result

[Jim Meyering]

Paul Eggert wrote:
> On 08/30/10 08:27, Eric Blake wrote:
>> On 08/30/2010 08:29 AM, Bruce Korb wrote:
>>> Every now and then, I'm thumped on the head by something fairly silly.
>>> This warning is quite silly:
>>>
>>>     (void)fwrite(...)
>>
>> Gnulib has the ignore-value module for places where casting to void is
>> insufficient to shut up gcc.
>
> I share with Bruce Korb the dislike of casting to void, or using ignore_value.
> I realize there is a benefit to catching some bugs, but there is also a cost
> (a cost that can include causing more bugs), and in this case it's not at all
> clear that the benefit exceeds the cost.
>
> In controversial areas like this, we should look to the GNU coding standards
> for advice, and they state that one shouldn't cast to void, or use
> similar measures merely to satisfy a lint checker.  So I suggest that we
> not use ignore-value; instead, we should avoid the GCC options that
> generate these warnings.
>
> For gnulib, I suggest that we deprecate the ignore-value module.

Hi Paul,

fwrite is an exception in that its value really is ignorable,
if you know what you're doing.  Hence, the warn_unused_result
attribute on its declaration is the problem, not gcc, and not
the ignore-value module.

However, for the vast majority of the functions marked with this
attribute, ignoring the return value really is a bug in all but a
very small fraction of the use cases.

The solution here could be to make gnulib provide a better declaration of
fwrite: one without the offending attribute.  Deprecating ignore-value or
somehow disabling all warn_unused_result attributes would be overkill --
no reason to throw the baby out with the bathwater.