https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106611
Arthur O'Dwyer <arthur.j.odwyer at gmail dot com> changed:
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CC| |arthur.j.odwyer at gmail dot
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--- Comment #11 from Arthur O'Dwyer <arthur.j.odwyer at gmail dot com> ---
Jiang An wrote:
> I've mailed the LWG Chair to submit an LWG issue that requests clarification
> of "is known not to throw any exceptions".
> FYI, there's at least one library implementor holding the same opinion as
> yours.
> https://quuxplusone.github.io/blog/2023/04/17/noexcept-false-equals-default/
Quuxplusone here. :) I don't think this is LWG jurisdiction at all. This isn't
even a bug in libstdc++'s <type_traits>. This is purely a GCC core-language
bug. GCC's builtin __is_nothrow_constructible(T, T&&) simply returns the wrong
answer when the selected constructor is "trivial, but noexcept(false)."
// https://godbolt.org/z/5szW6KeWq
struct C {
C(C&&) noexcept(false) = default;
};
static_assert(!__is_nothrow_constructible(C, C&&));
// GCC+EDG fail; Clang+MSVC succeed
Notice that the builtin returns the correct answer when the selected
constructor is "non-trivial, noexcept(false), but still defaulted so we know it
can't throw." The problem is specifically with *trivial* ctors.
@jwakely, I propose that this issue should be recategorized as a compiler bug.
(And I'm also voting effectively "NAD" on LWG3967.)
