Hi! 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. Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? 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. --- gcc/cp/typeck2.cc.jj 2026-02-06 11:18:47.091639968 +0100 +++ gcc/cp/typeck2.cc 2026-02-16 11:27:50.385010224 +0100 @@ -2610,9 +2610,13 @@ build_functional_cast_1 (location_t loc, 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) + return error_mark_node; + pedwarn (loc, OPT_Wc__23_extensions, + "%<auto(x)%> only available with " + "%<-std=c++23%> or %<-std=gnu++23%>"); + } } else { --- gcc/cp/semantics.cc.jj 2026-02-12 18:49:18.465869495 +0100 +++ gcc/cp/semantics.cc 2026-02-16 11:28:28.803359539 +0100 @@ -3874,9 +3874,13 @@ finish_compound_literal (tree type, tree 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) + return error_mark_node; + 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) --- gcc/testsuite/g++.dg/cpp23/auto-fncast19.C.jj 2026-02-16 11:43:24.524190997 +0100 +++ gcc/testsuite/g++.dg/cpp23/auto-fncast19.C 2026-02-16 11:42:24.750203226 +0100 @@ -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); // { dg-error "no matching function for call to 'foo<int>\\\(int\\\)'" "" { target c++20_down } } +} Jakub
