This is the alias CTAD version of the CTAD bug PR93248, and the fix is the same: clear cp_unevaluated_operand so that the entire chain of DECL_ARGUMENTS gets substituted.
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for trunk/11? PR c++/101233 gcc/cp/ChangeLog: * pt.c (alias_ctad_tweaks): Clear cp_unevaluated_operand for substituting DECL_ARGUMENTS. gcc/testsuite/ChangeLog: * g++.dg/cpp2a/class-deduction-alias10.C: New test. --- gcc/cp/pt.c | 12 +++++++++--- gcc/testsuite/g++.dg/cpp2a/class-deduction-alias10.C | 10 ++++++++++ 2 files changed, 19 insertions(+), 3 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp2a/class-deduction-alias10.C diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c index c7bf7d412ca..bc0a0936579 100644 --- a/gcc/cp/pt.c +++ b/gcc/cp/pt.c @@ -29097,9 +29097,15 @@ alias_ctad_tweaks (tree tmpl, tree uguides) /* Substitute the deduced arguments plus the rewritten template parameters into f to get g. This covers the type, copyness, guideness, and explicit-specifier. */ - tree g = tsubst_decl (DECL_TEMPLATE_RESULT (f), targs, complain); - if (g == error_mark_node) - continue; + tree g; + { + /* Parms are to have DECL_CHAIN tsubsted, which would be skipped + if cp_unevaluated_operand. */ + cp_evaluated ev; + g = tsubst_decl (DECL_TEMPLATE_RESULT (f), targs, complain); + if (g == error_mark_node) + continue; + } DECL_USE_TEMPLATE (g) = 0; fprime = build_template_decl (g, gtparms, false); DECL_TEMPLATE_RESULT (fprime) = g; diff --git a/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias10.C b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias10.C new file mode 100644 index 00000000000..a473fff5dc7 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias10.C @@ -0,0 +1,10 @@ +// PR c++/101233 +// { dg-do compile { target c++20 } } + +template<class T, class U> +struct A { A(T, U); }; + +template<class T, class U> +using B = A<U, T>; + +using type = decltype(B{0, 0}); -- 2.32.0.264.g75ae10bc75