1 files changed, 63 insertions, 0 deletions
diff --git a/tests/ui/impl-trait/hidden-lifetimes.rs b/tests/ui/impl-trait/hidden-lifetimes.rs
new file mode 100644
index 00000000000..ae07c892768
--- /dev/null
+++ b/tests/ui/impl-trait/hidden-lifetimes.rs
@@ -0,0 +1,63 @@
+// Test to show what happens if we were not careful and allowed invariant
+// lifetimes to escape though an impl trait.
+//
+// Specifically we swap a long lived and short lived reference, giving us a
+// dangling pointer.
+
+use std::cell::RefCell;
+use std::rc::Rc;
+
+trait Swap: Sized {
+    fn swap(self, other: Self);
+}
+
+impl<T> Swap for &mut T {
+    fn swap(self, other: Self) {
+        std::mem::swap(self, other);
+    }
+}
+
+impl<T> Swap for Rc<RefCell<T>> {
+    fn swap(self, other: Self) {
+        <RefCell<T>>::swap(&self, &other);
+    }
+}
+
+// Here we are hiding `'b` making the caller believe that `&'a mut &'s T` and
+// `&'a mut &'l T` are the same type.
+fn hide_ref<'a, 'b, T: 'static>(x: &'a mut &'b T) -> impl Swap + 'a {
+    x
+    //~^ ERROR hidden type
+}
+
+fn dangle_ref() -> &'static [i32; 3] {
+    let mut res = &[4, 5, 6];
+    let x = [1, 2, 3];
+    hide_ref(&mut res).swap(hide_ref(&mut &x));
+    res
+}
+
+// Here we are hiding `'b` making the caller believe that `Rc<RefCell<&'s T>>`
+// and `Rc<RefCell<&'l T>>` are the same type.
+//
+// This is different to the previous example because the concrete return type
+// only has a single lifetime.
+fn hide_rc_refcell<'a, 'b: 'a, T: 'static>(x: Rc<RefCell<&'b T>>) -> impl Swap + 'a {
+    x
+    //~^ ERROR hidden type
+}
+
+fn dangle_rc_refcell() -> &'static [i32; 3] {
+    let long = Rc::new(RefCell::new(&[4, 5, 6]));
+    let x = [1, 2, 3];
+    let short = Rc::new(RefCell::new(&x));
+    hide_rc_refcell(long.clone()).swap(hide_rc_refcell(short));
+    let res: &'static [i32; 3] = *long.borrow();
+    res
+}
+
+fn main() {
+    // both will print nonsense values.
+    println!("{:?}", dangle_ref());
+    println!("{:?}", dangle_rc_refcell())
+}