https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112642
--- Comment #7 from Miro Palmu <miro.palmu at helsinki dot fi> ---
(In reply to Jonathan Wakely from comment #6)
> The examples in comment 4 do compile using libstdc++ on clang, if you use
> libstdc++ headers from after sept 29 (for trunk) or oct 21 (for gcc-13).
I was testing this on compiler explorer on clang 17.0.1 and it used gcc-13.2.0
libstdc++. Also tried it locally with clang 16.0.6 with gcc-13.2.1 libstdc++
Output:
$ cat prog.cpp
#include <string>
#include <utility>
int main() {
[](std::string s = {}) consteval {
std::string ss{ std::move(s) };
}();
}
$ clang prog.cpp -std=c++2b -stdlib=libstdc++
prog.cpp:4:5: error: call to consteval function 'main()::(anonymous
class)::operator()' is not a constant expression
[](std::string s = {}) consteval {
^
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/13.2.1/../../../../include/c++/13.2.1/bits/stl_construct.h:97:14:
note: construction of subobject of member '_M_local_buf' of union with no
active member is not allowed in a constant expression
{ return ::new((void*)__location) _Tp(std::forward<_Args>(__args)...); }
^
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/13.2.1/../../../../include/c++/13.2.1/bits/char_traits.h:272:6:
note: in call to 'construct_at(&ss.._M_local_buf[0], s.._M_local_buf[0])'
std::construct_at(__s1 + __i, __s2[__i]);
^
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/13.2.1/../../../../include/c++/13.2.1/bits/char_traits.h:443:11:
note: in call to 'copy(&ss.._M_local_buf[0], &s.._M_local_buf[0], 1)'
return __gnu_cxx::char_traits<char_type>::copy(__s1, __s2, __n);
^
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/13.2.1/../../../../include/c++/13.2.1/bits/basic_string.h:672:6:
note: in call to 'copy(&ss.._M_local_buf[0], &s.._M_local_buf[0], 1)'
traits_type::copy(_M_local_buf, __str._M_local_buf,
^
prog.cpp:5:21: note: in call to 'basic_string(s)'
std::string ss{ std::move(s) };
^
prog.cpp:4:5: note: in call to '&[](std::string s) {
std::string ss{std::move(s)};
}->operator()({{{{}}, &s.._M_local_buf[0]}, 0, {._M_local_buf = {0, 0, 0, 0, 0,
0, 0, 0, 0, 0, ...}}})'
[](std::string s = {}) consteval {
^
1 error generated.
