LWG4201 with-await-transform::await_transform should not use a deduced return type

Author: burblebee

source/exec.tex

@@ -2156,8 +2156,9 @@
         }
 
       template<@\exposconcept{has-as-awaitable}@<Derived> T>
-        decltype(auto) await_transform(T&& value)
-          noexcept(noexcept(std::forward<T>(value).as_awaitable(declval<Derived&>()))) {
+        auto await_transform(T&& value)
+          noexcept(noexcept(std::forward<T>(value).as_awaitable(declval<Derived&>())))
+          -> decltype(std::forward<T>(value).as_awaitable(declval<Derived&>())) {
           return std::forward<T>(value).as_awaitable(static_cast<Derived&>(*this));
         }
     };