Hi! The following testcase ICEs in -std=c++26 mode since my r16-4338 C++26 va_start changes. The problem is that if we have anything non-canonical in a function type with (...) in C++26 (or C23/C2Y) mode, in this case the R typedef on return type rather than void, then we try to build TYPE_CANONICAL for that, but weren't passing in the no_named_args_stdarg_p, so a type with TYPE_NO_NAMED_ARGS_STDARG_P flag set got TYPE_CANONICAL with TYPE_NO_NAMED_ARGS_STDARG_P flag cleared and comptypes then didn't like that as those aren't really compatible types (...) vs. the C89-ish () which even C++ uses for some type-generic etc. builtins.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? 2026-02-05 Jakub Jelinek <[email protected]> PR c++/123977 * tree.cc (build_function_type): Pass no_named_args_stdarg_p as last argument to recursive call. * g++.dg/cpp26/stdarg10.C: New test. --- gcc/tree.cc.jj 2026-02-05 15:53:47.603157855 +0100 +++ gcc/tree.cc 2026-02-05 16:51:48.511416898 +0100 @@ -7780,7 +7780,8 @@ build_function_type (tree value_type, tr gcc_assert (TYPE_STRUCTURAL_EQUALITY_P (t)); else if (any_noncanonical_p) TYPE_CANONICAL (t) = build_function_type (TYPE_CANONICAL (value_type), - canon_argtypes); + canon_argtypes, + no_named_args_stdarg_p); if (!COMPLETE_TYPE_P (t)) layout_type (t); --- gcc/testsuite/g++.dg/cpp26/stdarg10.C.jj 2026-02-05 16:56:58.543182179 +0100 +++ gcc/testsuite/g++.dg/cpp26/stdarg10.C 2026-02-05 16:56:41.575468671 +0100 @@ -0,0 +1,19 @@ +// PR c++/123977 +// { dg-do compile } + +typedef void R; +struct A { + R foo (...) const volatile; + void foo (); +}; + +template <class T> +struct B { + static void bar () { (T (A::*)) &A::foo; } +}; + +void +baz () +{ + B <R (...) const volatile>::bar; +} Jakub
