[Bug libstdc++/50871] libstdc++ should be built with -Wpedantic and/or -Wsystem-headers

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=50871

--- Comment #16 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jason Merrill from comment #15)
> (In reply to Jonathan Wakely from comment #14)
> > It's better than what we have today, but I'm not sure it's where we want to
> > get to in the long term.
> > 
> > I've been trying a patch  that allows the system_header pragma to be
> > disabled when building and testing.
> 
> How about using 
> 
> #pragma GCC diagnostic warning "-Wsystem-headers"
> 
> instead?

That doesn't work well, see PR 80472

> > This causes testsuite failures due to
> > warnings that can't be controlled by options or diagnostic pragmas:
> > 
> > /home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/cmath:
> > 47: error: #include_next is a GCC extension
> 
> Maybe leave off -Wpedantic for now.

Yep. It would be nice if we had __include_next, or could add __extension__ to
avoid those warnings.

> > /home/jwakely/build/powerpc64le-unknown-linux-gnu/libstdc++-v3/include/
> > complex:1951: warning: floating point suffix 'if' shadowed by implementation
> 
> This seems like a real issue.  Perhaps for C++14 and up we should disable
> the built-in complex suffixes.

See PR 79228