[Bug c++/122908] [modules] Member functions of class templates that have function friend definitions expose their bodies

[nshead at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122908

--- Comment #7 from Nathaniel Shead <nshead at gcc dot gnu.org> ---
...and the reason the friendFn instantiation in the purview matters is because
it's making Class considered decl-reachable, and so we think that the exposure
might actually be a problematic one and so complain.