[Bug libstdc++/110968] format out of bounds read on format("{:05L}",-1.f)

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110968

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Oh dear, I must have broken this function at some point while implementing
std::format:

      // Locale-specific format.
      basic_string<_CharT>
      _M_localize(basic_string_view<_CharT> __str, char __expc,
                  const locale& __loc) const
      {
        basic_string<_CharT> __lstr;

        if (__loc == locale::classic())
          return __lstr; // Nothing to do.

That just returns an empty string, which the caller then uses assuming it's
valid.