UI test for deprecation warning of casting enum implementing Drop

src/test/ui/cenum_impl_drop_cast.rs

@@ -0,0 +1,18 @@
+#![deny(cenum_impl_drop_cast)]
+
+enum E {
+    A = 0,
+}
+
+impl Drop for E {
+    fn drop(&mut self) {
+        println!("Drop");
+    }
+}
+
+fn main() {
+    let e = E::A;
+    let i = e as u32;
+    //~^ ERROR Cast `enum` implementing `Drop` `E` to integer `u32`
+    //~| WARN this was previously accepted
+}

src/test/ui/cenum_impl_drop_cast.stderr

@@ -0,0 +1,16 @@
+error: Cast `enum` implementing `Drop` `E` to integer `u32`
+  --> $DIR/cenum_impl_drop_cast.rs:15:13
+   |
+LL |     let i = e as u32;
+   |             ^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/cenum_impl_drop_cast.rs:1:9
+   |
+LL | #![deny(cenum_impl_drop_cast)]
+   |         ^^^^^^^^^^^^^^^^^^^^
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #73333 <https://github.com/rust-lang/rust/issues/73333>
+
+error: aborting due to previous error
+