[Bug c++/50810] c++0x-compat does not warn about narrowing conversions

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50810

--- Comment #5 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2011-10-22 01:24:25 UTC ---
(In reply to comment #4)
> (In reply to comment #3)
> > (detail: not sure about the 'if (!warn_narrowing) return;' at the beginning of
> > check_narrowing: probably we don't want -Wno-narrowing to suppress the warnings
> > enabled of -Wc++0x-compat)
> 
> I think what you want is that -Wc++0x-compat enables -Wnarrowing independently
> of -std=, but still -Wc++0x-compat -Wno-narrowing should disable it. See the
> handling of Wlonglong in c-opts.c. So:
> 
>   if (!ok)
>     {
>       if (cxx_dialect != cxx98)
>         pedwarn (input_location, OPT_Wnarrowing, "narrowing conversion of %qE "
>             "from %qT to %qT inside { }", init, ftype, type);
>       else
>         warning_at (input_location, OPT_Wnarrowing, "narrowing conversion of
> %qE "
>             "from %qT to %qT inside { }", init, ftype, type);
>     }
> 

You can even make this more compact by using emit_diagnostic:

emit_diagnostic ((cxx_dialect != cxx98) ? DK_PEDWARN : DK_WARNING,
                 input_location, OPT_Wnarrowing,
                 "narrowing conversion of %qE from %qT to %qT inside { }", 
                  init, ftype, type);

The C FE has wrappers around something similar called pedwarn_c99, that is, a
pedwarn in C99, otherwise just a warning. You could add something similar to
C++.