https://gcc.gnu.org/g:5ee5a05da06078975a933be849431eee1d4c6989
commit r16-4211-g5ee5a05da06078975a933be849431eee1d4c6989 Author: Jason Merrill <[email protected]> Date: Fri Oct 3 18:10:36 2025 +0100 c++: concepts and conversions, take 2 [PR122127] My r16-4115 changed convert_template_argument (when called from instantiate_alias_template) to take the maybe_convert_nontype_argument path rather than convert_nontype_argument for this testcase. This meant not folding the use of the by-ref capture in the template argument to constant 1. When we come back to convert_template_argument again when substituting into resize<_Np> we strip the IMPLICIT_CONV_EXPR (since the types are the same) and take the convert_nontype_argument path, but at this point we've pushed into the alias template context and trying to fold away the capture fails because current_lambda_expr() is now null. Taking the convert_nontype_argument path in the same-type case where we would later strip an IMPLICIT_CONV_EXPR fixes the problem. Note that maybe_convert_nontype_argument already shares the same-type check with the stripping, but that isn't enough; it still doesn't fold away the capture proxy. PR c++/122127 PR c++/112632 gcc/cp/ChangeLog: * pt.cc (convert_template_argument): Don't add redundant IMPLICIT_CONV_EXPR. gcc/testsuite/ChangeLog: * g++.dg/cpp0x/lambda/lambda-template18.C: New test. Diff: --- gcc/cp/pt.cc | 7 +++++-- gcc/testsuite/g++.dg/cpp0x/lambda/lambda-template18.C | 11 +++++++++++ 2 files changed, 16 insertions(+), 2 deletions(-) diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc index bd60d515653b..9b32049e71be 100644 --- a/gcc/cp/pt.cc +++ b/gcc/cp/pt.cc @@ -8928,8 +8928,11 @@ convert_template_argument (tree parm, orig_arg = TREE_OPERAND (orig_arg, 0); if (!uses_template_parms (t) - && !(force_conv ? uses_template_parms (orig_arg) - : type_dependent_expression_p (orig_arg))) + && !type_dependent_expression_p (orig_arg) + && !(force_conv + && !(same_type_ignoring_top_level_qualifiers_p + (TREE_TYPE (orig_arg), t)) + && value_dependent_expression_p (orig_arg))) /* We used to call digest_init here. However, digest_init will report errors, which we don't want when complain is zero. More importantly, digest_init will try too diff --git a/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-template18.C b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-template18.C new file mode 100644 index 000000000000..e5e6e6a875b9 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-template18.C @@ -0,0 +1,11 @@ +// PR c++/122127 +// { dg-do compile { target c++11 } } + +template <int> struct resize; +template <int _Np> using resize_t = resize<_Np>; +template <class _Ap> struct basic_mask { + void _M_chunk() { + constexpr int __rem = 1; + [&] { resize_t<__rem>(); }(); + } +};
