[Bug c++/90291] [8/9/10 Regression] Inline namespace erroneously extends another namespace

[nathan at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90291

--- Comment #9 from Nathan Sidwell <nathan at gcc dot gnu.org> ---
Thanks for the context.  Clang intends to, but does not yet, implement DR2061. 
which is why you're seeing the different behaviour there, at least.

Continuig discussion on the C++ Core list,