test for special things that are now possible

tests/run-pass/stacked-borrows.rs

@@ -4,6 +4,8 @@ fn main() {
     read_does_not_invalidate1();
     read_does_not_invalidate2();
     ref_raw_int_raw();
+    mut_shr_raw();
+    mut_raw_then_mut_shr();
 }
 
 // Deref a raw ptr to access a field of a large struct, where the field
@@ -48,3 +50,29 @@ fn ref_raw_int_raw() {
     let xraw = xref as *mut i32 as usize as *mut i32;
     assert_eq!(unsafe { *xraw }, 3);
 }
+
+// Creating a raw from a `&mut` through an `&` works, even if we
+// write through that raw.
+fn mut_shr_raw() {
+    let mut x = 2;
+    {
+        let xref = &mut x;
+        let xraw = &*xref as *const i32 as *mut i32;
+        unsafe { *xraw = 4; }
+    }
+    assert_eq!(x, 4);
+}
+
+// Escape a mut to raw, then share the same mut and use the share, then the raw.
+// That should work.
+fn mut_raw_then_mut_shr() {
+    let mut x = 2;
+    {
+        let xref = &mut x;
+        let xraw = &mut *xref as *mut _;
+        let xshr = &*xref;
+        assert_eq!(*xshr, 2);
+        unsafe { *xraw = 4; }
+    }
+    assert_eq!(x, 4);
+}