Show that a test still fails with the feature gate enabled

Author: oli-obk

tests/ui/traits/const-traits/issue-103677.cnst.stderr

@@ -0,0 +1,9 @@
+error[E0277]: the trait bound `String: const Deref` is not satisfied
+  --> $DIR/issue-103677.rs:6:5
+   |
+LL |     &*s as &str;
+   |     ^^^
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/traits/const-traits/issue-103677.rs

@@ -1,5 +1,10 @@
-//@ check-pass
+//@[stock] check-pass
+//@ revisions: stock cnst
+#![cfg_attr(cnst, feature(const_trait_impl))]
 
-const _: fn(&String) = |s| { &*s as &str; };
+const _: fn(&String) = |s| {
+    &*s as &str;
+    //[cnst]~^ ERROR: the trait bound `String: const Deref` is not satisfied
+};
 
 fn main() {}