https://gcc.gnu.org/g:4e56ca07b9eeb9dd765893b34c147ca398a57f71
commit r17-1925-g4e56ca07b9eeb9dd765893b34c147ca398a57f71 Author: Marek Polacek <[email protected]> Date: Fri Jun 26 14:09:38 2026 -0400 c++/reflection: consteval-only type in splice-spec [PR125900] In this test in the template for the std::println("{}", static_cast<int>(s.[:member:])); line provokes a bogus "consteval-only expressions are only allowed in a constant-evaluated context" error. (Not the line before because there we have an OVERLOAD because the second argument's type isn't obvious, and so the whole thing is considered type-dep.) A splice-specifier is [: constant-expression :], and [expr.const.defns]: an expression or conversion is manifestly constant-evaluated if it is a constant-expression. So I think we shouldn't walk SPLICE_EXPRs in check_out_of_consteval_use_r. PR c++/125900 gcc/cp/ChangeLog: * reflect.cc (check_out_of_consteval_use_r): Don't walk SPLICE_EXPR. gcc/testsuite/ChangeLog: * g++.dg/reflect/expr18.C: New test. Reviewed-by: Jason Merrill <[email protected]> Diff: --- gcc/cp/reflect.cc | 4 ++++ gcc/testsuite/g++.dg/reflect/expr18.C | 25 +++++++++++++++++++++++++ 2 files changed, 29 insertions(+) diff --git a/gcc/cp/reflect.cc b/gcc/cp/reflect.cc index 3d6d24eb23ac..73e160d700f8 100644 --- a/gcc/cp/reflect.cc +++ b/gcc/cp/reflect.cc @@ -8760,6 +8760,10 @@ check_out_of_consteval_use_r (tree *tp, int *walk_subtrees, void *pset) || TREE_CODE (t) == DECL_EXPR /* Neither into USING_STMT. */ || TREE_CODE (t) == USING_STMT + /* The operand of a splice is a constant-expression, thus + manifestly constant-evaluated, so consteval-only types are permitted + here. */ + || TREE_CODE (t) == SPLICE_EXPR /* Blocks can appear in the TREE_VEC operand of OpenMP depend/affinity/map/to/from OMP_CLAUSEs when using iterators. */ || TREE_CODE (t) == BLOCK) diff --git a/gcc/testsuite/g++.dg/reflect/expr18.C b/gcc/testsuite/g++.dg/reflect/expr18.C new file mode 100644 index 000000000000..f2ceefc6f883 --- /dev/null +++ b/gcc/testsuite/g++.dg/reflect/expr18.C @@ -0,0 +1,25 @@ +// PR c++/125900 +// { dg-do compile { target c++26 } } +// { dg-additional-options "-freflection" } + +#include <meta> +#include <print> + +struct S { + float f; +}; + +int main() { + S s{.f = 1.5f}; + + constexpr auto member{^^S::f}; + std::println("{}", s.[:member:]); + std::println("{}", static_cast<int>(s.[:member:])); + + constexpr auto access_context{std::meta::access_context::current()}; + template for (constexpr auto member : + std::define_static_array(nonstatic_data_members_of(^^S, access_context))) { + std::println("{}", s.[:member:]); + std::println("{}", static_cast<int>(s.[:member:])); + } +}
