https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86643
--- Comment #1 from Tobias Burnus <burnus at gcc dot gnu.org> ---
Culprit is r262474 - "P0935R0 Eradicating unnecessarily explicit default
constructors"
Looking closer at the example, it doesn't use std::basic_ostringstream as
advertised but:
std::ostringstream buf2("test", std::ios_base::ate);
The "std::ostringstream" is deprecated and replacing it by
std::basic_ostringstream<char> buf2("test", std::ios_base::ate);
works.
The question is whether the patch intended to remove the deprecated support for
std::ostringstream or not. If it did, I think that warrens an entry at
https://gcc.gnu.org/gcc-9/changes.html ; if not, then it needs to be fixed.
Cross ref:
P0935R0 is http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0935r0.html
Patch causing the regression is
https://gcc.gnu.org/ml/gcc-patches/2018-07/msg00318.html
