https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120917
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |INVALID
Status|UNCONFIRMED |RESOLVED
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Frank Heckenbach from comment #0)
> Is that correct? (The message could really have been much clearer about
> that.)
Yes.
> The problem is, I never asked for non-standard features. I ran g++-12 (and
> previous versions) with "--std=c++23" (or respective versions) only, not
> with any GNU extension flags (definitely never "-fconcepts" or
> "-fconcepts-ts"), to avoid exactly these kinds of problems.
Then you're doing it wrong, using -std=c++NN options has never disabled all
extensions, and that is documented:
When a base standard is specified, the compiler accepts all programs
following that
standard plus those using GNU extensions that do not contradict it. For
example,
-std=c90 turns off certain features of GCC that are incompatible with ISO
C90,
such as the "asm" and "typeof" keywords, but not other GNU extensions that do
not
have a meaning in ISO C90, such as omitting the middle term of a "?:"
expression."
This extension uses syntax which is not valid in C++20 so it does not conflict
with the base standard, and is always enabled. You should have been using
-pedantic if you wanted to diagnose all extensions:
without this option, certain GNU extensions and traditional C and C++
features are
supported as well. With this option, they are diagnosed (or rejected with
-pedantic-errors).
> In the assumption that this a part of standard concepts, I've used it in
> many places in my code, and now GCC tells me it's not and the feature is
> disappearing, is that right?
yes
> So basically GCC lured me into a trap, and the trap is snapping now, is it?
No. You didn't read the manual and assumed something about -std=c++23 which has
never been true.
> Is there an alternative (apart from the manual boilerplate)? Even if it's an
> evil macro, I don't care at this point.
Just write the function template out:
template<typename T> void f (S <T>);
> Is there any chance the feature will be added to the standard sometime in
> the future?
No, I am not aware of any plans to propose it for the standard.
> Even if not, could GCC please (re-)add this feature (of course, with an
> explicit option this time), because of the special circumstances?
I don't see any special circumstances.
