Hi! This PR complains that [[maybe_unused]] attribute is ignored on the range-for-declaration of expansion-statement.
We copy DECL_ATTRIBUTES and apply late attributes, but early attributes don't have their handlers called again, so some extra flags need to be copied as well. This copies TREE_USED and DECL_READ_P flags. Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? 2025-11-22 Jakub Jelinek <[email protected]> PR c++/122788 * pt.cc (finish_expansion_stmt): Or in TREE_USED and DECL_READ_P flags from range_decl to decl or from corresponding structured binding to this_decl. * g++.dg/cpp26/expansion-stmt27.C: New test. --- gcc/cp/pt.cc.jj 2025-11-20 08:19:24.741372896 +0100 +++ gcc/cp/pt.cc 2025-11-21 10:07:06.664153996 +0100 @@ -32900,6 +32900,8 @@ finish_expansion_stmt (tree expansion_st type = tsubst (type, args, complain | tf_tst_ok, in_decl); tree decl = build_decl (loc, VAR_DECL, DECL_NAME (range_decl), type); DECL_ATTRIBUTES (decl) = DECL_ATTRIBUTES (range_decl); + TREE_USED (decl) |= TREE_USED (range_decl); + DECL_READ_P (decl) |= DECL_READ_P (range_decl); if (args) apply_late_template_attributes (&decl, DECL_ATTRIBUTES (decl), /*flags=*/0, args, complain, @@ -32958,6 +32960,8 @@ finish_expansion_stmt (tree expansion_st DECL_ARTIFICIAL (this_decl) = 1; DECL_ATTRIBUTES (this_decl) = DECL_ATTRIBUTES (TREE_VEC_ELT (v, i + 1)); + TREE_USED (this_decl) |= TREE_USED (TREE_VEC_ELT (v, i + 1)); + DECL_READ_P (this_decl) |= DECL_READ_P (TREE_VEC_ELT (v, i + 1)); if (DECL_PACK_P (TREE_VEC_ELT (v, i + 1))) { tree dtype = cxx_make_type (DECLTYPE_TYPE); --- gcc/testsuite/g++.dg/cpp26/expansion-stmt27.C.jj 2025-11-21 09:53:51.311857261 +0100 +++ gcc/testsuite/g++.dg/cpp26/expansion-stmt27.C 2025-11-21 10:04:23.130656298 +0100 @@ -0,0 +1,17 @@ +// PR c++/122788 +// { dg-do compile { target c++14 } } +// { dg-options "-Wunused" } + +void +foo () +{ + template for ([[maybe_unused]] auto i : { 42 }) // { dg-warning "'template for' only available with" "" { target c++23_down } } + ; // { dg-bogus "unused variable 'i'" "" { target *-*-* } .-1 } + template for ([[maybe_unused]] auto j : { 1, 2, 3 }) // { dg-warning "'template for' only available with" "" { target c++23_down } } + { // { dg-bogus "unused variable 'j'" "" { target *-*-* } .-1 } +#if __cpp_if_constexpr >= 201606 + if constexpr (false) + (void) j; +#endif + } +} Jakub
