add test checking that Vec push/pop does not invalidate pointers

Author: RalfJung

src/liballoc/tests/vec.rs

@@ -1152,3 +1152,24 @@ fn test_try_reserve_exact() {
     }
 
 }
+
+#[test]
+fn test_stable_push_pop() {
+    // Test that, if we reserved enough space, adding and removing elements does not
+    // invalidate references into the vector (such as `v0`).  This test also
+    // runs in Miri, which would detect such problems.
+    let mut v = Vec::with_capacity(10);
+    v.push(13);
+
+    // laundering the lifetime -- we take care that `v` does not reallocate, so that's okay.
+    let v0 = unsafe { &*(&v[0] as *const _) };
+
+    // Now do a bunch of things and occasionally use `v0` again to assert it is still valid.
+    v.push(1);
+    v.push(2);
+    v.insert(1, 1);
+    assert_eq!(*v0, 13);
+    v.remove(1);
+    v.pop().unwrap();
+    assert_eq!(*v0, 13);
+}