https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124456
--- Comment #9 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <[email protected]>: https://gcc.gnu.org/g:4f9e2843084b7934a27337ae57bd3313723a5c9b commit r16-8091-g4f9e2843084b7934a27337ae57bd3313723a5c9b Author: Jakub Jelinek <[email protected]> Date: Sat Mar 14 09:52:42 2026 +0100 c++: Fix up partial instantiation of structured binding packs [PR124456] The following testcase ICEs during partial instantiation of structured binding pack. tsubst_pack_expansion assumed DECL_VALUE_EXPR in that case will be TREE_VEC containing what should be expanded. But when the initializer of the structured bindings is still type dependent, we know neither the size of the sb pack nor its content, cp_finish_decomp in that case doesn't set DECL_VALUE_EXPR to a TREE_VEC at all, but to ARRAY_REF of the base and index within the structured binding (and pack if any). tsubst_pack_expansion can set arg_pack to NULL_TREE and in that case else { /* We can't substitute for this parameter pack. We use a flag as well as the missing_level counter because function parameter packs don't have a level. */ gcc_assert (processing_template_decl || is_auto (parm_pack) || args == NULL_TREE); unsubstituted_packs = true; } will trigger and later on in the function unsubstituted_packs is handled properly. So, the following patch makes sure to set arg_pack to NULL_TREE in that case. 2026-03-14 Jakub Jelinek <[email protected]> PR c++/124456 * pt.cc (tsubst_pack_expansion): For structured binding pack with type dependent pack set arg_pack to NULL_TREE. * g++.dg/cpp26/decomp27.C: New test.
