[PATCH v2] c++: Don't quote nothrow in diagnostic

Marek Polacek polacek@redhat.com
Tue Sep 27 13:00:56 GMT 2022


On Tue, Sep 27, 2022 at 10:41:29AM +0200, Richard Biener wrote:
> On Mon, Sep 26, 2022 at 9:54 PM Marek Polacek <polacek@redhat.com> wrote:
> >
> > On Mon, Sep 26, 2022 at 12:34:04PM -0400, Jason Merrill wrote:
> > > On 9/26/22 03:50, Richard Biener wrote:
> > > > On Fri, Sep 23, 2022 at 8:41 PM Marek Polacek via Gcc-patches
> > > > <gcc-patches@gcc.gnu.org> wrote:
> > > > >
> > > > > In <https://gcc.gnu.org/pipermail/gcc-patches/2022-September/602057.html>
> > > > > Jason noticed that we quote "nothrow" in diagnostics even though it's
> > > > > not a keyword in C++.  Just removing the quotes didn't work because
> > > > > then -Wformat-diag complains, so this patch replaces it with "no-throw".
> > > > >
> > > > > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> > > >
> > > > That doesn't look like an improvement to me.  Can we quote 'nothrow()' instead?
> >
> > Understood.
> >
> > > nothrow() is a syntax error; the C++11 keyword is 'noexcept'. std::nothrow
> > > is a dummy placement argument used to indicate that a new-expression should
> > > return null rather than throw on failure.
> > >
> > > But bizarrely, the library traits use the word "nothrow".  Marek's patch
> > > clarifies that we are not trying to refer to anything in the language.
> > >
> > > > I'd rather leave it alone than changing it to no-throw.  Why does -Wformat-diag
> > > > complain?  If we shouldn't quote nothrow that should be adjusted?
> > >
> > > I think -Wformat-diag complains because "nothrow" is an attribute; it also
> > > includes some other attribute names in the list of "keywords".
> > >
> > > I would also be fine with just removing the quotes and removing nothrow from
> > > c_keywords.
> >
> > Like below?   Bootstrapped/regtested on x86_64-pc-linux-gnu.
> 
> Yes.  I assume that terms like "nothrow constructible" are used in the
> C++ standard?

I don't really see that.  [meta.unary.prop] says "known not to throw any
exceptions" for the _nothrow built-ins.  That may be too long to use in
diagnostics.  And the warning would probably complain about the unquoted
'throw' in it.  :)
 
> > Note that now I see warnings with my system compiler (gcc-12.2.1).  Can
> > I commit the c-format.cc hunk to gcc 12 so that eventually even gcc 12
> > stops warning?
> 
> Sure.

Thanks.

Marek



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