Test that const_precise_live_drops can't be depended upon stably

src/test/ui/consts/stable-precise-live-drops-in-libcore.rs

@@ -0,0 +1,22 @@
+#![stable(feature = "core", since = "1.6.0")]
+#![feature(staged_api)]
+#![feature(const_precise_live_drops, const_fn)]
+
+enum Either<T, S> {
+    Left(T),
+    Right(S),
+}
+
+impl<T> Either<T, T> {
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_stable(feature = "foo", since = "1.0.0")]
+    pub const fn unwrap(self) -> T {
+        //~^ ERROR destructors cannot be evaluated at compile-time
+        match self {
+            Self::Left(t) => t,
+            Self::Right(t) => t,
+        }
+    }
+}
+
+fn main() {}

src/test/ui/consts/stable-precise-live-drops-in-libcore.stderr

@@ -0,0 +1,12 @@
+error[E0493]: destructors cannot be evaluated at compile-time
+  --> $DIR/stable-precise-live-drops-in-libcore.rs:13:25
+   |
+LL |     pub const fn unwrap(self) -> T {
+   |                         ^^^^ constant functions cannot evaluate destructors
+...
+LL |     }
+   |     - value is dropped here
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0493`.

src/test/ui/consts/unstable-precise-live-drops-in-libcore.rs

@@ -0,0 +1,23 @@
+// check-pass
+
+#![stable(feature = "core", since = "1.6.0")]
+#![feature(staged_api)]
+#![feature(const_precise_live_drops)]
+
+enum Either<T, S> {
+    Left(T),
+    Right(S),
+}
+
+impl<T> Either<T, T> {
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_unstable(feature = "foo", issue = "none")]
+    pub const fn unwrap(self) -> T {
+        match self {
+            Self::Left(t) => t,
+            Self::Right(t) => t,
+        }
+    }
+}
+
+fn main() {}