libstdc++: Fix narrowing conversion in std::visit

Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
libstdc++-v3/ChangeLog:

	* include/std/variant (__do_visit): Use variant_npos instead of
	literal -1 that requires a narrowing conversion.

diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant
index ddeefd9b35e0cbe503610dd17a1ab34a2b593fce..d50c6b7de1d439e0ac3c480b34238e8e068604ae 100644 (file)
--- a/libstdc++-v3/include/std/variant
+++ b/libstdc++-v3/include/std/variant
@@ -1830,7 +1830,8 @@ namespace __variant
                  if constexpr (is_same_v<_Result_type, __variant_idx_cookie>
                                || is_same_v<_Result_type, __variant_cookie>)
                    {
-                     return __gen_vtable_impl<_Ma, index_sequence<-1>>::
+                     using _Npos = index_sequence<variant_npos>;
+                     return __gen_vtable_impl<_Ma, _Npos>::
                        __visit_invoke(std::forward<_Visitor>(__visitor),
                                       std::forward<_V0>(__v0));
                    }