[Bug libstdc++/28103] std::operator<<(ostream&, string) sets badbit instead of failbit on failure

["redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=28103

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
It looks like we've been setting badbit in ostream::_M_write(const charT*,
streamsize) since it was added in r0-47606-g8d0a564bba54f7

That function was used to replace the similar code in basic_ostream::write:

          streamsize __put = this->rdbuf()->sputn(__s, __n);
          if ( __put != __n)
            this->setstate(ios_base::badbit);

and in the operator<< for std::basic_string:

          streamsize __res = __out.rdbuf()->sputn(__s, __len);
          __out.width(0);
          if (__res != __len)
            __out.setstate(ios_base::failbit);

However that created the problem, because basic_ostream::write is indeed
specified to set badbit but the string inserter sets failbit.

[ostream.unformatted] says:
"inserting in the output sequence fails (in which case the function calls
setstate(badbit)"

[string.io] defers to [string.view.io] which defers to [ostream.formatted]
which says:
"If the generation fails, then the formatted output function does
setstate(ios_base::failbit)"

So we have different requirements for ostream::write and string insertion, but
we implement them both the same way since r0-47606-g8d0a564bba54f7 (the
_M_write member was later replaced  by __ostream_write but that uses the same
logic and sets badbit).