Re: [PATCH][RFC] Add quotes for constexpr keyword.

[Martin Sebor <msebor at gmail dot com>]

On 11/15/2017 09:38 AM, Jonathan Wakely wrote:
> On 15/11/17 09:30 -0700, Martin Sebor wrote:
> > On 11/15/2017 05:45 AM, Martin Liška wrote:
> > > On 11/06/2017 07:29 PM, Martin Sebor wrote:
> > > > Sorry for being late with my comment.  I just spotted this minor
> > > > formatting issue.  Even though GCC isn't (yet) consistent about
> > > > it the keyword "constexpr" should be quoted in the error message
> > > > below (and, eventually, in all diagnostic messages).  Since the
> > > > patch has been committed by now this is just a reminder for us
> > > > to try to keep this in mind in the future.
> > >
> > > Hi.
> > >
> > > I've prepared patch for that. If it's desired, I can fix test-suite
> > > follow-up.
> > > Do we want to change it also for error messages like:
> > > "call to non-constexpr function"
> > > "constexpr call flows off the end of the function"
> >
> > If GCC had support for italics for defined terms of the language
> > or the grammar /constexpr function/ would be italicized because
> > it's a defined term.  Absent that, I think I would quote them all
> > for consistency.
> >
> > Martin
> >
> > PS I checked the C++ standard to see how it used the term and
> > the choices it makes seem pretty arbitrary.  There are even
> > sentences with two instances of two word, one in fixed width
> > font and the other in proportional.  So I don't think we can
> > use the spec as an example to follow.
>
> Did you check the latest draft? That should have been fixed.
>
> Defined terms should only be italicized when introduced, not when
> used, e.g. in [dcl.constexpr] p2 "constexpr function" and "constexpr
> constructor" are italicized, but are in normal font elsewhere. When
> referring specifically to the keyword `constexpr` it should be in code
> font.
>
> Grammar productions are always italicized, but "constexpr function" is
> not a grammar production.

Right, /constexpr function/ is a defined term (as is /constexpr
cosntructor/ and /constexpr if/).  As you say, its defining
occurrence is italicized in the text, and the rest aren't.
In contrast, in terms like "constexpr specifier," "constexpr"
is the keyword and it's always in monospace.

The challenge in GCC as I see it is to know how to decide which
of the two it is.  The difference between constexpr the keyword
and constexpr as part of a defined term is too subtle for most
people who don't work with the standard for a living.  So we end
up with these minor inconsistencies in the diagnostics.  I think
the easiest way to achieve consistency (in diagnostics) it is to
always quote keywords.  Having italics would be a nice touch but
it would probably not improve consistency.

Martin

PS I was looking at the February 2017 draft.  The October version
looks quite a bit better.