Hi! For -fno-exceptions, we reject throw statements in the source, and a lot of code in the header has #ifdef __cpp_exceptions guarded stuff and the FE for !flag_exceptions doesn't emit some parts of the IL needed for exceptions. For the errors in metafns, we had just a todo to handle it in the source but no actual implementation, so we allowed throwing an exception and sometimes it worked to some extent and sometimes it didn't.
The following patch fixes it by not throwing an exception if user asked for -fno-exceptions - instead we just emit an error including the planned what () (unless ctx->quiet) and make the evaluation non-constant. Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? 2026-03-10 Jakub Jelinek <[email protected]> PR c++/124417 * reflect.cc (get_meta_exception_object): Add CTX argument. For !flag_exceptions emit error unless ctx->quiet, set *non_constant_p to true and return NULL_TREE instead of throwing an exception. (throw_exception): Adjust get_meta_exception_object caller. * g++.dg/reflect/no-exceptions1.C: New test. --- gcc/cp/reflect.cc.jj 2026-03-09 11:41:58.060768044 +0100 +++ gcc/cp/reflect.cc 2026-03-09 18:09:08.967171309 +0100 @@ -929,17 +929,31 @@ get_info_vec (location_t loc, const cons and FROM is the info for from(). */ static tree -get_meta_exception_object (location_t loc, const char *what, tree from, - bool *non_constant_p) +get_meta_exception_object (location_t loc, const constexpr_ctx *ctx, + const char *what, tree from, bool *non_constant_p) { /* Don't throw in a template. */ - // TODO For -fno-exceptions, report an error. if (processing_template_decl) { *non_constant_p = true; return NULL_TREE; } + /* Don't try to throw exceptions with -fno-exceptions. */ + if (!flag_exceptions) + { + if (!cxx_constexpr_quiet_p (ctx)) + { + auto_diagnostic_group d; + error_at (loc, "%qD should throw %qs; %<what()%>: %qs", + from, "std::meta::exception", _(what)); + inform (loc, "exceptions are disabled, treating as non-constant; " + "use %qs to enable", "-fexceptions"); + } + *non_constant_p = true; + return NULL_TREE; + } + tree type = lookup_qualified_name (std_meta_node, "exception", LOOK_want::TYPE, /*complain*/true); if (TREE_CODE (type) != TYPE_DECL || !CLASS_TYPE_P (TREE_TYPE (type))) @@ -984,7 +998,8 @@ static tree throw_exception (location_t loc, const constexpr_ctx *ctx, const char *msgid, tree from, bool *non_constant_p, tree *jump_target) { - if (tree obj = get_meta_exception_object (loc, msgid, from, non_constant_p)) + if (tree obj = get_meta_exception_object (loc, ctx, msgid, from, + non_constant_p)) *jump_target = cxa_allocate_and_throw_exception (loc, ctx, obj); return NULL_TREE; } --- gcc/testsuite/g++.dg/reflect/no-exceptions1.C.jj 2026-03-09 18:39:33.749487279 +0100 +++ gcc/testsuite/g++.dg/reflect/no-exceptions1.C 2026-03-09 18:41:50.131194162 +0100 @@ -0,0 +1,10 @@ +// PR c++/124417 +// { dg-do compile { target c++26 } } +// { dg-additional-options "-freflection -fno-exceptions" } + +#include <meta> + +auto a = is_enum_type (^^::); +// { dg-error "call to consteval function 'std::meta::is_enum_type\\\(\\\^\\\^::\\\)' is not a constant expression" "" { target *-*-* } .-1 } +// { dg-error "'consteval bool std::meta::is_enum_type\\\(info\\\)' should throw 'std::meta::exception'; 'what\\\(\\\)': 'reflection does not represent a type'" "" { target *-*-* } .-2 } +// { dg-message "exceptions are disabled, treating as non-constant; use '-fexceptions' to enable" "" { target *-*-* } .-3 } Jakub
