[Bug c++/104294] ICE: tree check: accessed elt 2 of 'tree_vec' with 1 elts in tsubst_pack_expansion, at cp/pt.cc:13130

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104294

--- Comment #2 from Patrick Palka <ppalka at gcc dot gnu.org> ---
I believe the testcase should be valid even without the user-defined deduction
guide since we should have synthesized an equivalent guide from the C(T)
constructor.