https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78209
--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
This seems to fix it:
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -27598,6 +27598,8 @@ do_auto_deduction (tree type, tree init, tree
auto_node,
else if (AUTO_IS_DECLTYPE (auto_node))
{
tree stripped_init = tree_strip_any_location_wrapper (init);
+ if (REFERENCE_REF_P (stripped_init))
+ stripped_init = TREE_OPERAND (stripped_init, 0);
bool id = (DECL_P (stripped_init)
|| ((TREE_CODE (init) == COMPONENT_REF
|| TREE_CODE (init) == SCOPE_REF)
(then id is true and decltype deduces the right type).
