Re: [PATCH v2] c++: add deprecation notice for -fconcepts-ts

[Marek Polacek <polacek@redhat.com>]

On Wed, Jan 31, 2024 at 02:00:18PM -0500, Jason Merrill wrote:
> On 1/31/24 10:55, Marek Polacek wrote:
> > On Wed, Jan 31, 2024 at 08:53:00AM -0500, Jason Merrill wrote:
> > > On 1/31/24 03:40, Richard Biener wrote:
> > > > On Wed, Jan 31, 2024 at 12:19 AM Marek Polacek <polacek@redhat.com> wrote:
> > > > > 
> > > > > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> > > > > 
> > > > > -- >8 --
> > > > > We plan to deprecate -fconcepts-ts in GCC 15 and remove the flag_concepts_ts
> > > > > code.  This note is an admonishing reminder to convert the Concepts TS
> > > > > code to C++20 Concepts.
> > > > 
> > > > What does "deprecated in GCC 15" mean?  Given you output the notice with
> > > > GCC 14 it would be better to state when it's going to be removed -
> > > > it's effectively
> > > > "deprecated" right now then?  Or will it continue to "work" forever
> > > > until it bitrots?
> > 
> > Sorry for the wrong choice of words.  I meant deprecated now, removed later.
> > > Agreed, it's deprecated now.  We talked about it having no effect in GCC 15;
> > > the message could say that.  Or we could leave it vague and just say it's
> > > deprecated.
> > > 
> > > Please also update invoke.texi.
> > 
> > Like this?
> 
> Hmm, I'm not sure whether we want to actually remove the option or just the
> support, as with -fcilkplus.  I was assuming the latter, in which case the
> patch could use some further rewording, but perhaps in the case of
> extensions like this (and Cilk+) it makes sense to actually remove the
> option.  Any other opinions?

I assumed that we'd turn fconcepts-ts into "Ignore", since we've kept
even options like fdeduce-init-list or ffor-scope around.

I suppose in GCC 15 it should be marked as WarnRemoved, but fcilkplus isn't
WarnRemoved, so I'm not sure.

Should I have said "ignored in GCC 15"?
 
> > -- >8 --
> > We plan to remove -fconcepts-ts in GCC 15 and thus remove the flag_concepts_ts
> > code.  This note is an admonishing reminder to convert the Concepts TS
> > code to C++20 Concepts.
> > 
> > gcc/c-family/ChangeLog:
> > 
> > 	* c-opts.cc (c_common_post_options): Add an inform saying that
> > 	-fconcepts-ts is deprecated and will be removed in GCC 15.
> > 
> > gcc/ChangeLog:
> > 
> > 	* doc/invoke.texi: Mention that -fconcepts-ts was deprecated in GCC 14.
> > ---
> >   gcc/c-family/c-opts.cc | 5 +++++
> >   gcc/doc/invoke.texi    | 4 +++-
> >   2 files changed, 8 insertions(+), 1 deletion(-)
> > 
> > diff --git a/gcc/c-family/c-opts.cc b/gcc/c-family/c-opts.cc
> > index b38a1225ac4..b845aff2226 100644
> > --- a/gcc/c-family/c-opts.cc
> > +++ b/gcc/c-family/c-opts.cc
> > @@ -1139,6 +1139,11 @@ c_common_post_options (const char **pfilename)
> >     if (cxx_dialect >= cxx20 || flag_concepts_ts)
> >       flag_concepts = 1;
> > +  /* -fconcepts-ts will be removed in GCC 15.  */
> > +  if (flag_concepts_ts)
> > +    inform (input_location, "%<-fconcepts-ts%> is deprecated and will be "
> > +	    "removed in GCC 15; please convert your code to C++20 concepts");
> > +
> >     /* -fimmediate-escalation has no effect when immediate functions are not
> >        supported.  */
> >     if (flag_immediate_escalation && cxx_dialect < cxx20)
> > diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> > index eb931b984e8..ca2c0e90452 100644
> > --- a/gcc/doc/invoke.texi
> > +++ b/gcc/doc/invoke.texi
> > @@ -3204,7 +3204,9 @@ the language standard, so @option{-fconcepts} defaults to on.
> >   Some constructs that were allowed by the earlier C++ Extensions for
> >   Concepts Technical Specification, ISO 19217 (2015), but didn't make it
> >   into the standard, can additionally be enabled by
> > -@option{-fconcepts-ts}.
> > +@option{-fconcepts-ts}.  The option @option{-fconcepts-ts} was deprecated
> > +in GCC 14 and may be removed in GCC 15; users are expected to convert
> > +their code to C++20 concepts.
> >   @opindex fconstexpr-depth
> >   @item -fconstexpr-depth=@var{n}
> > 
> > base-commit: f7935beef7b02fbba0adf33fb2ba5c0a27d7e9ff
> 

Marek