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

[Jason Merrill <jason@redhat.com>]

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?

> -- >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