[PATCH] Warn on empty switch statements

[Reid Kleckner]

On Wed, May 29, 2013 at 3:49 PM, Richard Smith <richard at metafoo.co.uk>wrote:

> On Wed, May 29, 2013 at 7:35 AM, Aaron Ballman <aaron at aaronballman.com>wrote:
>
>> -Wunreachable-code doesn't warn on empty statement bodies for the
>> switch.  So, for instance:
>>
>> int main() {
>>   int i = 0;
>>   switch(i) {}
>> }
>>
>> yields no warnings in clang with -Wunreachable-code (or -Wall), but at
>> /W3 in MSVC you get: warning C4060: switch statement contains no
>> 'case' or 'default' labels.  Will it catch lots of bugs?  Probably
>> not.  But it also should have basically no false positives either.  It
>> would be nice for people who want their code to also be warning-free
>> under MSVC.
>
>
> I think we need more justification for adding the warning than this.
>
> It doesn't seem reasonable to expect us to implement the union of all
> warnings which every existent compiler produces. Some of those warnings are
> really dumb. For instance, /W3 also enables C4800, which I don't think we
> will ever want to implement.
>

I agree that warning (forcing value to bool) is really, really bad, and I
hope most serious projects turn it off.

However, I can say it's pretty annoying if you're working on cross-platform
project and have to push to another platform to build just to get some
compiler warnings for a compiler which you're expected to keep warning
clean, value judgements about its diagnostic quality aside.  That cycle is
long and painful, and if you skip it people often yell at you.

While clang will never be able to paper over the differences between
platforms, having some off-by-default diagnostics like this could save
users some time and increase the likelihood that their changes Just Work on
the first push.
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