@@ -11891,6 +11891,11 @@ cp_parser_lambda_declarator_opt (cp_parser* parser, tree lambda_expr)
"lambda templates are only available with "
"%<-std=c++20%> or %<-std=gnu++20%>");
+ /* Even though the whole lambda may be a default argument, its
+ template-parameter-list is a context where it's OK to create
+ new parameters. */
+ auto lvf = make_temp_override (parser->local_variables_forbidden_p, 0u);
+
cp_lexer_consume_token (parser->lexer);
template_param_list = cp_parser_template_parameter_list (parser);
@@ -20978,8 +20983,8 @@ cp_parser_placeholder_type_specifier (cp_parser *parser, location_t loc,
/* In a default argument we may not be creating new parameters. */
if (parser->local_variables_forbidden_p & LOCAL_VARS_FORBIDDEN)
{
- /* If this assert turns out to be false, do error() instead. */
- gcc_assert (tentative);
+ if (!tentative)
+ error_at (loc, "local variables may not appear in this context");
return error_mark_node;
}
return build_constrained_parameter (con, proto, args);
new file mode 100644
@@ -0,0 +1,8 @@
+// PR c++/109859
+// { dg-do compile { target c++20 } }
+
+template<class>
+concept C = true;
+
+template <class = C> // { dg-error "may not appear in this context" }
+int f();
new file mode 100644
@@ -0,0 +1,10 @@
+// PR c++/109859
+// { dg-do compile { target c++20 } }
+
+template<typename>
+concept A = true;
+
+template<auto = []<A a> {}>
+int x;
+
+void g() { (void) x<>; }