[Bug c++/107340] std::unordered_map and completeness of nested classes

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107340

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
And the standard says it's undefined to use incomplete classes with
unordered_map.