Add wrong_covariance_unsize_coercion invalid program test

tests-extra/invalid/wrong_covariance_unsize_coercion.rs

@@ -0,0 +1,32 @@
+use std::cell::RefCell;
+use std::fmt;
+
+use self_cell::self_cell;
+
+self_cell! {
+ struct WrongVarianceExample {
+ owner: (),
+
+ #[covariant]
+ dependent: Dependent,
+ }
+}
+
+// this type is not covariant
+type Dependent<'a> = RefCell<Box<dyn fmt::Display + 'a>>;
+
+fn main() {
+ let cell = WrongVarianceExample::new((), |_| RefCell::new(Box::new("")));
+ let s = String::from("Hello World");
+
+ // borrow_dependent unsound due to incorrectly checked variance
+ *cell.borrow_dependent().borrow_mut() = Box::new(s.as_str());
+
+ // s still exists
+ cell.with_dependent(|_, d| println!("{}", d.borrow()));
+
+ drop(s);
+
+ // s is gone
+ cell.with_dependent(|_, d| println!("{}", d.borrow()));
+}

tests-extra/invalid/wrong_covariance_unsize_coercion.stderr

@@ -0,0 +1,16 @@
+error[E0623]: lifetime mismatch
+ --> $DIR/wrong_covariance_unsize_coercion.rs:6:1
+ |
+6 | / self_cell! {
+7 | | struct WrongVarianceExample {
+8 | | owner: (),
+9 | |
+... |
+12 | | }
+13 | | }
+ | | ^
+ | | |
+ | |_these two types are declared with different lifetimes...
+ | ...but data from `x` flows into `x` here
+ |
+ = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)