Merge pull request #738 from RalfJung/stacked-borrows-2

test for new read rules

Author: RalfJung

tests/compile-fail/stacked_borrows/interior_mut1.rs

@@ -3,8 +3,13 @@ use std::cell::UnsafeCell;
 fn main() { unsafe {
     let c = &UnsafeCell::new(UnsafeCell::new(0));
     let inner_uniq = &mut *c.get();
-    let inner_shr = &*inner_uniq; // a SharedRW with a tag
-    *c.get() = UnsafeCell::new(1); // invalidates the SharedRW
+    // stack: [c: SharedReadWrite, inner_uniq: Unique]
+
+    let inner_shr = &*inner_uniq; // adds a SharedReadWrite
+    // stack: [c: SharedReadWrite, inner_uniq: Unique, inner_shr: SharedReadWrite]
+
+    *c.get() = UnsafeCell::new(1); // invalidates inner_shr
+    // stack: [c: SharedReadWrite]
+
     let _val = *inner_shr.get(); //~ ERROR borrow stack
-    let _val = *inner_uniq.get();
 } }

tests/compile-fail/stacked_borrows/interior_mut2.rs

@@ -0,0 +1,28 @@
+use std::cell::UnsafeCell;
+use std::mem;
+
+// Like `&mut *x.get()`, but without intermediate raw pointers.
+#[allow(mutable_transmutes)]
+unsafe fn unsafe_cell_get<T>(x: &UnsafeCell<T>) -> &'static mut T {
+    mem::transmute(x)
+}
+
+fn main() { unsafe {
+    let c = &UnsafeCell::new(UnsafeCell::new(0));
+    let inner_uniq = &mut *c.get();
+    let inner_shr = &*inner_uniq;
+    // stack: [c: SharedReadWrite, inner_uniq: Unique, inner_shr: SharedReadWrite]
+
+    let _val = c.get().read(); // invalidates inner_uniq
+    // stack: [c: SharedReadWrite, inner_uniq: Disabled, inner_shr: SharedReadWrite]
+
+    // We have to be careful not to add any raw pointers above inner_uniq in
+    // the stack, hence the use of unsafe_cell_get.
+    let _val = *unsafe_cell_get(inner_shr); // this still works
+
+    *c.get() = UnsafeCell::new(0); // now inner_shr gets invalidated
+    // stack: [c: SharedReadWrite]
+
+    // now this does not work any more
+    let _val = *inner_shr.get(); //~ ERROR borrow stack
+} }