[Bug c++/127021] New: Writing to volatile qualified std::nullptr_t should not be valid in a constant expression

[luigighiron at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127021

            Bug ID: 127021
           Summary: Writing to volatile qualified std::nullptr_t should
                    not be valid in a constant expression
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: luigighiron at gmail dot com
  Target Milestone: ---

The following code is incorrectly accepted by GCC:

consteval void foo(){
    volatile decltype(nullptr)a=0;
    a=0;
}
int main(){
    foo();
}

Unlike with reading volatile qualified std::nullptr_t as in PR118661, writing
to an object with such a type does not have any exemption. Clang correctly
rejects this, MSVC and EDG also incorrectly accept this.