https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114275
--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
PR105320 seems similar.
Another maybe related testcase:
$ cat testcase.C
export module M;
template<class> struct A {
template<class> friend struct B;
};
A<int> a;
template<class> struct B { };
$ cat testcase.C | g++ -fmodules-ts -x c++ -
<stdin>:6:27: error: cannot declare ‘struct B< <template-parameter-1-1> >’ in a
different module
<stdin>:3:34: note: declared here
<stdin>:1:8: warning: not writing module ‘M’ due to errors
