https://gcc.gnu.org/g:daa030592bdd082c8a4452df5fddc98686d51003
commit r15-10903-gdaa030592bdd082c8a4452df5fddc98686d51003 Author: Jakub Jelinek <[email protected]> Date: Tue Feb 17 08:59:06 2026 +0100 c++: Don't support auto{x} and auto(x) for C++ < 23 in SFINAE contexts [PR120685] The following testcase ICEs in C++ 20 and older, because during diagnostics dump_template_bindings attempts to tsubst with tf_none something and we try to emit a pedwarn during that. While the pedwarn could be just guarded with if (complain & tf_warning), I thought we shouldn't support extensions for tf_none and should instead return error_mark_node. The following patch does that. This is a backport version which instead of not supporting it just doesn't emit the pedwarn in SFINAE contexts for C++ < 23 but still supports it. 2026-02-17 Jakub Jelinek <[email protected]> PR c++/120685 * typeck2.cc (build_functional_cast_1): For C++23 auto(x) without tf_warning or tf_error return error_mark_node instead of emitting pedwarn and handling it. * semantics.cc (finish_compound_literal): Similarly for C++26 auto{x}. * g++.dg/cpp23/auto-fncast19.C: New test. (cherry picked from commit f7efb7e62ac96c082ff72549d9b3789f5c955efe) Diff: --- gcc/cp/semantics.cc | 9 ++++++--- gcc/cp/typeck2.cc | 9 ++++++--- gcc/testsuite/g++.dg/cpp23/auto-fncast19.C | 12 ++++++++++++ 3 files changed, 24 insertions(+), 6 deletions(-) diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc index 0b5584c10e7c..46e7baaea1f7 100644 --- a/gcc/cp/semantics.cc +++ b/gcc/cp/semantics.cc @@ -3834,9 +3834,12 @@ finish_compound_literal (tree type, tree compound_literal, return error_mark_node; } else if (cxx_dialect < cxx23) - pedwarn (input_location, OPT_Wc__23_extensions, - "%<auto{x}%> only available with " - "%<-std=c++23%> or %<-std=gnu++23%>"); + { + if ((complain & tf_warning_or_error) != 0) + pedwarn (input_location, OPT_Wc__23_extensions, + "%<auto{x}%> only available with " + "%<-std=c++23%> or %<-std=gnu++23%>"); + } type = do_auto_deduction (type, compound_literal, type, complain, adc_variable_type); if (type == error_mark_node) diff --git a/gcc/cp/typeck2.cc b/gcc/cp/typeck2.cc index 45edd1801739..1ed20ce921c0 100644 --- a/gcc/cp/typeck2.cc +++ b/gcc/cp/typeck2.cc @@ -2509,9 +2509,12 @@ build_functional_cast_1 (location_t loc, tree exp, tree parms, return error_mark_node; } else if (cxx_dialect < cxx23) - pedwarn (loc, OPT_Wc__23_extensions, - "%<auto(x)%> only available with " - "%<-std=c++23%> or %<-std=gnu++23%>"); + { + if ((complain & tf_warning_or_error) != 0) + pedwarn (loc, OPT_Wc__23_extensions, + "%<auto(x)%> only available with " + "%<-std=c++23%> or %<-std=gnu++23%>"); + } } else { diff --git a/gcc/testsuite/g++.dg/cpp23/auto-fncast19.C b/gcc/testsuite/g++.dg/cpp23/auto-fncast19.C new file mode 100644 index 000000000000..05a0dbd2f39e --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp23/auto-fncast19.C @@ -0,0 +1,12 @@ +// PR c++/120685 +// { dg-do compile { target c++11 } } +// { dg-options "" } + +template <typename T> +void foo (decltype (auto (T ())) x) {} // { dg-warning "'auto\\\(x\\\)' only available with" "" { target c++20_down } } + +int +main () +{ + foo <int> (1); +}
