do_class_deduction handles specially the case where we're deducing one placeholder from another equivalent one, but here the initializer passed to do_class_deduction is wrapped in an EXPR_PACK_EXPANSION (we're being called from unify during get_partial_spec_bindings). This patch makes do_class_deduction look through EXPR_PACK_EXPANSIONs so that we detect this case as well.
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for trunk or perhaps stage1? gcc/cp/ChangeLog: PR c++/97134 * pt.c (do_class_deduction): Look through EXPR_PACK_EXPANSION when checking if the initializer is an equivalent class placeholder template parameter. gcc/testsuite/ChangeLog: PR c++/97134 * g++.dg/cpp2a/nontype-class43.C: New test. --- gcc/cp/pt.c | 6 +++++- gcc/testsuite/g++.dg/cpp2a/nontype-class43.C | 11 +++++++++++ 2 files changed, 16 insertions(+), 1 deletion(-) create mode 100644 gcc/testsuite/g++.dg/cpp2a/nontype-class43.C diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c index 01c807be1bb..872b08ec9ad 100644 --- a/gcc/cp/pt.c +++ b/gcc/cp/pt.c @@ -29265,7 +29265,11 @@ do_class_deduction (tree ptype, tree tmpl, tree init, return ptype; /* Initializing one placeholder from another. */ - if (init && TREE_CODE (init) == TEMPLATE_PARM_INDEX + if (init + && (TREE_CODE (init) == TEMPLATE_PARM_INDEX + || (TREE_CODE (init) == EXPR_PACK_EXPANSION + && (TREE_CODE (PACK_EXPANSION_PATTERN (init)) + == TEMPLATE_PARM_INDEX))) && is_auto (TREE_TYPE (init)) && CLASS_PLACEHOLDER_TEMPLATE (TREE_TYPE (init)) == tmpl) return cp_build_qualified_type (TREE_TYPE (init), cp_type_quals (ptype)); diff --git a/gcc/testsuite/g++.dg/cpp2a/nontype-class43.C b/gcc/testsuite/g++.dg/cpp2a/nontype-class43.C new file mode 100644 index 00000000000..f51684f7a62 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/nontype-class43.C @@ -0,0 +1,11 @@ +// PR c++/97134 +// { dg-do compile { target c++20 } } + +template<typename T> +struct templ {}; + +template<templ... Vs> +struct wrapper {}; + +template<templ... Vs> requires true +struct wrapper<Vs...> {}; -- 2.31.1.272.g89b43f80a5