[Bug libstdc++/120650] New: Error of requesting %d form month_day_last is not detected at compile time

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120650

            Bug ID: 120650
           Summary: Error of requesting %d form month_day_last is not
                    detected at compile time
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tkaminsk at gcc dot gnu.org
  Target Milestone: ---

The following code throws format_error at runtime, instead of being ill-formed:
```
#include <chrono>
#include <format>

int main()
{
  using namespace std::chrono;
  auto s = std::format("{:%d}", January/last);
}
```
https://godbolt.org/z/rrGedrhxv