merge two SB test files

Author: RalfJung

tests/pass/stacked-borrows/interior_mutability.rs

@@ -1,5 +1,5 @@
 // compile-flags: -Zmiri-retag-fields
-use std::cell::{Cell, RefCell, UnsafeCell};
+use std::cell::{Cell, Ref, RefCell, RefMut, UnsafeCell};
 use std::mem::{self, MaybeUninit};
 
 fn main() {
@@ -9,6 +9,10 @@ fn main() {
     unsafe_cell_2phase();
     unsafe_cell_deallocate();
     unsafe_cell_invalidate();
+    refcell_basic();
+    ref_protector();
+    ref_mut_protector();
+    rust_issue_68303();
 }
 
 fn aliasing_mut_and_shr() {
@@ -100,3 +104,72 @@ fn unsafe_cell_invalidate() {
     // So using raw1 invalidates raw2.
     f(unsafe { mem::transmute(raw2) }, raw1);
 }
+
+fn refcell_basic() {
+    let c = RefCell::new(42);
+    {
+        let s1 = c.borrow();
+        let _x: i32 = *s1;
+        let s2 = c.borrow();
+        let _x: i32 = *s1;
+        let _y: i32 = *s2;
+        let _x: i32 = *s1;
+        let _y: i32 = *s2;
+    }
+    {
+        let mut m = c.borrow_mut();
+        let _z: i32 = *m;
+        {
+            let s: &i32 = &*m;
+            let _x = *s;
+        }
+        *m = 23;
+        let _z: i32 = *m;
+    }
+    {
+        let s1 = c.borrow();
+        let _x: i32 = *s1;
+        let s2 = c.borrow();
+        let _x: i32 = *s1;
+        let _y: i32 = *s2;
+        let _x: i32 = *s1;
+        let _y: i32 = *s2;
+    }
+}
+
+// Adding a Stacked Borrows protector for `Ref` would break this
+fn ref_protector() {
+    fn break_it(rc: &RefCell<i32>, r: Ref<'_, i32>) {
+        // `r` has a shared reference, it is passed in as argument and hence
+        // a protector is added that marks this memory as read-only for the entire
+        // duration of this function.
+        drop(r);
+        // *oops* here we can mutate that memory.
+        *rc.borrow_mut() = 2;
+    }
+
+    let rc = RefCell::new(0);
+    break_it(&rc, rc.borrow())
+}
+
+fn ref_mut_protector() {
+    fn break_it(rc: &RefCell<i32>, r: RefMut<'_, i32>) {
+        // `r` has a shared reference, it is passed in as argument and hence
+        // a protector is added that marks this memory as inaccessible for the entire
+        // duration of this function
+        drop(r);
+        // *oops* here we can mutate that memory.
+        *rc.borrow_mut() = 2;
+    }
+
+    let rc = RefCell::new(0);
+    break_it(&rc, rc.borrow_mut())
+}
+
+/// Make sure we do not have bad enum layout optimizations.
+fn rust_issue_68303() {
+    let optional = Some(RefCell::new(false));
+    let mut handle = optional.as_ref().unwrap().borrow_mut();
+    assert!(optional.is_some());
+    *handle = true;
+}