c++: generic lambda forwarding function [PR94546]
While instantiating test(Plot) we partially instantiate the generic lambda.
We look at forward<T>(rest)... and see that it's just replacing parameter
packs with new parameter packs and tries to do a direct substitution. But
because register_parameter_specializations had built up a
NONTYPE_ARGUMENT_PACK around the new parameter pack, the substitution
failed. So let's not wrap it that way.
gcc/cp/ChangeLog
2020-04-22 Jason Merrill <jason@redhat.com>
PR c++/94546
* pt.c (register_parameter_specializations): If the instantiation is
still a parameter pack, don't wrap it in a NONTYPE_ARGUMENT_PACK.
(tsubst_pack_expansion, tsubst_expr): Adjust.