https://gcc.gnu.org/g:a03c244f530346ed04a3ecac0c718d83ed7fae47
commit r15-10319-ga03c244f530346ed04a3ecac0c718d83ed7fae47 Author: Patrick Palka <[email protected]> Date: Fri Sep 12 14:21:25 2025 -0400 c++: pack indexing is a non-deduced context [PR121795] We weren't explicitly treating a pack index specifier as a non-deduced context (as per [temp.deduct.type]/5), leading to an ICE for the first testcase below. PR c++/121795 gcc/cp/ChangeLog: * pt.cc (unify) <case PACK_INDEX_TYPE>: New non-deduced context case. gcc/testsuite/ChangeLog: * g++.dg/cpp26/pack-indexing17.C: New test. * g++.dg/cpp26/pack-indexing17a.C: New test. Reviewed-by: Marek Polacek <[email protected]> Reviewed-by: Jason Merrill <[email protected]> (cherry picked from commit 8e3230f4fed0d41e790d68c2534c057911bab35c) Diff: --- gcc/cp/pt.cc | 4 ++-- gcc/testsuite/g++.dg/cpp26/pack-indexing17.C | 11 +++++++++++ gcc/testsuite/g++.dg/cpp26/pack-indexing17a.C | 12 ++++++++++++ 3 files changed, 25 insertions(+), 2 deletions(-) diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc index 061691370757..3a3577f9d566 100644 --- a/gcc/cp/pt.cc +++ b/gcc/cp/pt.cc @@ -25975,8 +25975,8 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict, case TYPEOF_TYPE: case DECLTYPE_TYPE: case TRAIT_TYPE: - /* Cannot deduce anything from TYPEOF_TYPE, DECLTYPE_TYPE, - or TRAIT_TYPE nodes. */ + case PACK_INDEX_TYPE: + /* These are non-deduced contexts. */ return unify_success (explain_p); case ERROR_MARK: diff --git a/gcc/testsuite/g++.dg/cpp26/pack-indexing17.C b/gcc/testsuite/g++.dg/cpp26/pack-indexing17.C new file mode 100644 index 000000000000..8450ed64bd5f --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp26/pack-indexing17.C @@ -0,0 +1,11 @@ +// PR c++/121795 +// { dg-do compile { target c++26 } } + +template<class T, class... Ts> +struct A; + +template<class... Ts> +struct A<Ts...[sizeof...(Ts)-1], Ts...> { }; + +A<int, int> x; +A<char, int> y; // { dg-error "incomplete" } diff --git a/gcc/testsuite/g++.dg/cpp26/pack-indexing17a.C b/gcc/testsuite/g++.dg/cpp26/pack-indexing17a.C new file mode 100644 index 000000000000..445f0d94ad20 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp26/pack-indexing17a.C @@ -0,0 +1,12 @@ +// PR c++/121795 +// A version of pack-indexing17.C using a nontype pack. +// { dg-do compile { target c++26 } } + +template<int N, int... Ns> +struct A; + +template<int... Ns> +struct A<Ns...[sizeof...(Ns)-1], Ns...> { }; + +A<0, 0> x; +A<0, 1> y; // { dg-error "incomplete" }
