clang++ -std=c++2b and -std=c++23 fail, while clang++ w/o them and g++ pass. (both x86_64 trunk on Compiler Explorer)

use-of-incomplete-type-or-not.cpp

#include <memory>
#include <cassert>

struct Timer {
  void clear() { pimpl.reset(); }

private:
  struct Pimpl;
  std::unique_ptr<Pimpl> pimpl;
};

struct Timer::Pimpl {
};

int main() {
    Timer timer;
    timer.clear();
    return 0;
}