Auto merge of #1163 - RalfJung:raw-cast, r=RalfJung

Test raw-ptr-cast without reborrow

With rust-lang/rust#64588 landed, we can finally test these things adequately. :)

Author: bors

tests/compile-fail/stacked_borrows/illegal_read8.rs

@@ -0,0 +1,13 @@
+// Make sure that creating a raw ptr next to a shared ref works
+// but the shared ref still gets invalidated when the raw ptr is used for writing.
+
+fn main() { unsafe {
+    use std::mem;
+    let x = &mut 0;
+    let y1: &i32 = mem::transmute(&*x); // launder lifetimes
+    let y2 = x as *mut _;
+    let _val = *y2;
+    let _val = *y1;
+    *y2 += 1;
+    let _fail = *y1; //~ ERROR borrow stack
+} }

tests/run-pass/stacked-borrows/stacked-borrows.rs

@@ -108,7 +108,7 @@ fn drop_after_sharing() {
 
 // Make sure that coercing &mut T to *const T produces a writeable pointer.
 fn direct_mut_to_const_raw() {
-    // FIXME: This is currently disabled, waiting on a fix for <https://github.com/rust-lang/rust/issues/56604>
+    // TODO: This is currently disabled, waiting on a decision on <https://github.com/rust-lang/rust/issues/56604>
     /*let x = &mut 0;
     let y: *const i32 = x;
     unsafe { *(y as *mut i32) = 1; }
@@ -119,26 +119,21 @@ fn direct_mut_to_const_raw() {
 // Make sure that we can create two raw pointers from a mutable reference and use them both.
 fn two_raw() { unsafe {
     let x = &mut 0;
-    // Given the implicit reborrows, the only reason this currently works is that we
-    // do not track raw pointers: The creation of `y2` reborrows `x` and thus pops
-    // `y1` off the stack.
     let y1 = x as *mut _;
     let y2 = x as *mut _;
     *y1 += 2;
     *y2 += 1;
 } }
 
 // Make sure that creating a *mut does not invalidate existing shared references.
-fn shr_and_raw() { /* unsafe {
+fn shr_and_raw() { unsafe {
     use std::mem;
-    // FIXME: This is currently disabled because "as *mut _" incurs a reborrow.
     let x = &mut 0;
     let y1: &i32 = mem::transmute(&*x); // launder lifetimes
     let y2 = x as *mut _;
     let _val = *y1;
     *y2 += 1;
-    // TODO: Once this works, add compile-fail test that tries to read from y1 again.
-} */ }
+} }
 
 fn disjoint_mutable_subborrows() {
     struct Foo {
@@ -165,5 +160,5 @@ fn disjoint_mutable_subborrows() {
     let b = unsafe{ borrow_field_b(ptr) };
     b.push(4);
     a.push_str(" world");
-    dbg!(a,b);
+    eprintln!("{:?} {:?}", a, b);
 }

tests/run-pass/stacked-borrows/stacked-borrows.stderr

@@ -1,7 +1 @@
-[$DIR/stacked-borrows.rs:168] a = "hello world"
-[$DIR/stacked-borrows.rs:168] b = [
-    0,
-    1,
-    2,
-    4,
-]
+"hello world" [0, 1, 2, 4]