[Bug c++/121068] Placement new of array element is rejected at compile-time

[tkaminsk at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121068

--- Comment #14 from Tomasz Kamiński <tkaminsk at gcc dot gnu.org> ---
Not sure if this is expected, so noting this here.

On trunk (with r16-2432-gfdbc5ff61b471076cc9c758fb6c30d62f7ef1c56), if I value
initialize the array (like in inplace_vector), then the code works:
  union { S a[20]; };
  new (&a) S[20](); // OK
  for (int i = 0; i < 20; ++i)
    a[i].~S();

  auto* sf = ::new(&a[2]) S(11);
See also: https://gcc.gnu.org/pipermail/libstdc++/2025-July/062752.html

But after changing the placement new to perform default initialization `new
(&a) S`, the above code no longer works. This is not a blocker on any library
feature.