https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71568
--- Comment #3 from Jason Merrill <jason at gcc dot gnu.org> --- The issue is that even though nlog_custom is public in D, the pointer-to-member expression ends up being &F<D>::nlog_custom, and F (i.e. tuple) inherits privately from C, so nlog_custom is private in F. As a result, clang also rejects the testcase in comment 1, because it doesn't select the partial specialization. The G++ bug is giving a hard error for the access violation rather than quietly not selecting the partial specialization.
