Add test for #59023

src/test/ui/traits/impl_trait_as_trait_return_position.rs

@@ -0,0 +1,17 @@
+// check-pass
+
+trait A {
+    type Foo;
+}
+
+impl<T> A for T {
+    type Foo = ();
+}
+
+fn foo() -> impl std::borrow::Borrow<<u8 as A>::Foo> {
+    ()
+}
+
+fn main() {
+    foo();
+}