Re: Unsure about a new warning in mainline

[Paolo Carlini <pcarlini at suse dot de>]

Hi Roger

and thanks for your explanations. Just a couple of additional remarks.

> I agree with Paolo that this is a change for C++, and should at least be
> documented in changes.html, and probably be tweaked to avoid warning in
> system headers.
>  
Note that, AFAICS, the issue would boil down to fixing pragma 
system_headers to work with templates. I don't think it's trivial and / 
or someone is already working on it. In any case, if we agree that the 
warning is meaningful, our (v3) policy asks for avoiding it in the code, 
whenever possible: in short, I mean to change v3 in any case.

> Specifically, for PR 30465 "((T)1 << 31) - 1" is potentially undefined
> when  T is a 32-bit signed type, but well-defined if T is unsigned or
> wider than 32-bits.
>  
FYI: this specific issue arises from std::numeric_limits<wchar_t> on 
x86-linux: in particular from the __glibcxx_max macro at the beginning 
of the header. Luckily, since we are dealing with template 
specializations, the pragma is sufficient to suppress the warning, but 
if you can figure out a better way to compute the max itself, just speak...

Thanks,
Paolo.