[dcl.type.auto.deduct]/5 "If the placeholder-type-specifier is of the
form type-constraintopt decltype(auto), T shall be the placeholder alone."
So, only plain decltype(auto) is allowed. But we aren't diagnosing it in
function declarations, because do_auto_deduction is never called for those.
Bootstrapped/regtested on x86_64-linux, ok for trunk?
2019-09-08 Marek Polacek <polacek@redhat.com>
PR c++/84374 - diagnose invalid uses of decltype(auto).
* decl.c (grokdeclarator): Diagnose wrong usage of decltype(auto) in
a function declaration.
* g++.dg/cpp1y/auto-fn57.C: New test.
diff --git gcc/cp/decl.c gcc/cp/decl.c
index 88e2c3beb2b..b1777730934 100644
--- gcc/cp/decl.c
+++ gcc/cp/decl.c
@@ -11560,6 +11560,14 @@ grokdeclarator (const cp_declarator *declarator,
"cannot have deduced return type");
virtualp = false;
}
+ else if (is_auto (auto_node)
+ && AUTO_IS_DECLTYPE (auto_node)
+ && type != auto_node)
+ {
+ error_at (typespec_loc, "%qT as type rather than "
+ "plain %<decltype(auto)%>", type);
+ return error_mark_node;
+ }
}
else if (!is_auto (type) && sfk != sfk_conversion)
{
@@ -11580,6 +11588,16 @@ grokdeclarator (const cp_declarator *declarator,
"invalid use of %<decltype(auto)%>");
return error_mark_node;
}
+ else if (tree a = type_uses_auto (late_return_type))
+ {
+ if (AUTO_IS_DECLTYPE (a) && a != late_return_type)
+ {
+ error_at (typespec_loc, "%qT as type rather than "
+ "plain %<decltype(auto)%>",
+ late_return_type);
+ return error_mark_node;
+ }
+ }