librustc: Remove cross borrowing from mutable Boxes to &mut.

This will break code like:

    fn f(x: &mut int) {}

    let mut a = box 1i;
    f(a);

Change it to:

    fn f(x: &mut int) {}

    let mut a = box 1i;
    f(&mut *a);

RFC 33; issue #10504.

[breaking-change]

Author: pcwalton

src/libcollections/dlist.rs

@@ -156,12 +156,12 @@ impl<T> DList<T> {
     fn push_front_node(&mut self, mut new_head: Box<Node<T>>) {
         match self.list_head {
             None => {
-                self.list_tail = Rawlink::some(new_head);
+                self.list_tail = Rawlink::some(&mut *new_head);
                 self.list_head = link_with_prev(new_head, Rawlink::none());
             }
             Some(ref mut head) => {
                 new_head.prev = Rawlink::none();
-                head.prev = Rawlink::some(new_head);
+                head.prev = Rawlink::some(&mut *new_head);
                 mem::swap(head, &mut new_head);
                 head.next = Some(new_head);
             }
@@ -188,7 +188,7 @@ impl<T> DList<T> {
         match self.list_tail.resolve() {
             None => return self.push_front_node(new_tail),
             Some(tail) => {
-                self.list_tail = Rawlink::some(new_tail);
+                self.list_tail = Rawlink::some(&mut *new_tail);
                 tail.next = link_with_prev(new_tail, Rawlink::some(tail));
             }
         }
@@ -379,7 +379,7 @@ impl<T> DList<T> {
     #[inline]
     pub fn mut_iter<'a>(&'a mut self) -> MutItems<'a, T> {
         let head_raw = match self.list_head {
-            Some(ref mut h) => Rawlink::some(*h),
+            Some(ref mut h) => Rawlink::some(&mut **h),
             None => Rawlink::none(),
         };
         MutItems{
@@ -530,7 +530,7 @@ impl<'a, A> MutItems<'a, A> {
                     Some(prev) => prev,
                 };
                 let node_own = prev_node.next.take_unwrap();
-                ins_node.next = link_with_prev(node_own, Rawlink::some(ins_node));
+                ins_node.next = link_with_prev(node_own, Rawlink::some(&mut *ins_node));
                 prev_node.next = link_with_prev(ins_node, Rawlink::some(prev_node));
                 self.list.length += 1;
             }

src/libcollections/treemap.rs

@@ -482,7 +482,7 @@ fn mut_deref<K, V>(x: &mut Option<Box<TreeNode<K, V>>>)
              -> *mut TreeNode<K, V> {
     match *x {
         Some(ref mut n) => {
-            let n: &mut TreeNode<K, V> = *n;
+            let n: &mut TreeNode<K, V> = &mut **n;
             n as *mut TreeNode<K, V>
         }
         None => ptr::mut_null()

src/libcore/any.rs

@@ -183,7 +183,7 @@ mod tests {
         let mut b = box 7u;
 
         let a_r = &mut a as &mut Any;
-        let tmp: &mut uint = b;
+        let tmp: &mut uint = &mut *b;
         let b_r = tmp as &mut Any;
 
         match a_r.as_mut::<uint>() {

src/libgreen/sched.rs

@@ -641,7 +641,7 @@ impl Scheduler {
             };
 
             let (current_task_context, next_task_context) =
-                Scheduler::get_contexts(current_task, next_task);
+                Scheduler::get_contexts(current_task, &mut *next_task);
 
             // Done with everything - put the next task in TLS. This
             // works because due to transmute the borrow checker

src/librustc/middle/typeck/infer/coercion.rs

@@ -248,7 +248,12 @@ impl<'f> Coerce<'f> {
         let r_borrow = self.get_ref().infcx.next_region_var(coercion);
 
         let inner_ty = match *sty_a {
-            ty::ty_box(typ) | ty::ty_uniq(typ) => typ,
+            ty::ty_box(typ) | ty::ty_uniq(typ) => {
+                if mt_b.mutbl == ast::MutMutable {
+                    return Err(ty::terr_mutability)
+                }
+                typ
+            }
             ty::ty_rptr(_, mt_a) => mt_a.ty,
             _ => {
                 return self.subtype(a, b);

src/librustc/util/sha2.rs

@@ -599,7 +599,7 @@ mod tests {
 
         let mut sh = box Sha256::new();
 
-        test_hash(sh, tests.as_slice());
+        test_hash(&mut *sh, tests.as_slice());
     }
 
     /// Feed 1,000,000 'a's into the digest with varying input sizes and check that the result is

src/libsync/raw.rs

@@ -899,7 +899,7 @@ mod tests {
             });
         }
         {
-            access_shared(sharedstate, &x, mode2, 10);
+            access_shared(&mut *sharedstate, &x, mode2, 10);
             let _ = rx.recv();
 
             assert_eq!(*sharedstate, 20);

src/test/bench/shootout-k-nucleotide.rs

@@ -115,16 +115,16 @@ impl Table {
                     count: 0,
                     next: None,
                 };
-                c.f(entry);
+                c.f(&mut *entry);
                 item.next = Some(entry);
             }
             Some(ref mut entry) => {
                 if entry.code == key {
-                    c.f(*entry);
+                    c.f(&mut **entry);
                     return;
                 }
 
-                Table::search_remainder(*entry, key, c)
+                Table::search_remainder(&mut **entry, key, c)
             }
         }
     }
@@ -139,7 +139,7 @@ impl Table {
                     count: 0,
                     next: None,
                 };
-                c.f(entry);
+                c.f(&mut *entry);
                 *self.items.get_mut(index as uint) = Some(entry);
                 return;
             }
@@ -148,11 +148,11 @@ impl Table {
         {
             let entry = &mut *self.items.get_mut(index as uint).get_mut_ref();
             if entry.code == key {
-                c.f(*entry);
+                c.f(&mut **entry);
                 return;
             }
 
-            Table::search_remainder(*entry, key, c)
+            Table::search_remainder(&mut **entry, key, c)
         }
     }
 

src/test/bench/sudoku.rs

@@ -138,7 +138,7 @@ impl Sudoku {
             let mut avail = box Colors::new(start_color);
 
             // drop colors already in use in neighbourhood
-            self.drop_colors(avail, row, col);
+            self.drop_colors(&mut *avail, row, col);
 
             // find first remaining color that is available
             let next = avail.next();

src/test/compile-fail/borrowck-lend-flow-if.rs

@@ -34,7 +34,7 @@ fn pre_freeze_cond() {
     if cond() {
         _w = &v;
     }
-    borrow_mut(v); //~ ERROR cannot borrow
+    borrow_mut(&mut *v); //~ ERROR cannot borrow
 }
 
 fn pre_freeze_else() {
@@ -46,7 +46,7 @@ fn pre_freeze_else() {
     if cond() {
         _w = &v;
     } else {
-        borrow_mut(v);
+        borrow_mut(&mut *v);
     }
 }
 

src/test/compile-fail/borrowck-lend-flow-loop.rs

@@ -53,7 +53,7 @@ fn loop_aliased_mut() {
     let mut w = box 4;
     let mut _x = &w;
     loop {
-        borrow_mut(v); //~ ERROR cannot borrow
+        borrow_mut(&mut *v); //~ ERROR cannot borrow
         _x = &v;
     }
 }
@@ -65,7 +65,7 @@ fn while_aliased_mut() {
     let mut w = box 4;
     let mut _x = &w;
     while cond() {
-        borrow_mut(v); //~ ERROR cannot borrow
+        borrow_mut(&mut *v); //~ ERROR cannot borrow
         _x = &v;
     }
 }
@@ -78,11 +78,11 @@ fn loop_aliased_mut_break() {
     let mut w = box 4;
     let mut _x = &w;
     loop {
-        borrow_mut(v);
+        borrow_mut(&mut *v);
         _x = &v;
         break;
     }
-    borrow_mut(v); //~ ERROR cannot borrow
+    borrow_mut(&mut *v); //~ ERROR cannot borrow
 }
 
 fn while_aliased_mut_break() {
@@ -92,11 +92,11 @@ fn while_aliased_mut_break() {
     let mut w = box 4;
     let mut _x = &w;
     while cond() {
-        borrow_mut(v);
+        borrow_mut(&mut *v);
         _x = &v;
         break;
     }
-    borrow_mut(v); //~ ERROR cannot borrow
+    borrow_mut(&mut *v); //~ ERROR cannot borrow
 }
 
 fn while_aliased_mut_cond(cond: bool, cond2: bool) {

src/test/compile-fail/borrowck-lend-flow.rs

@@ -30,14 +30,14 @@ fn pre_freeze() {
 
     let mut v = box 3;
     let _w = &v;
-    borrow_mut(v); //~ ERROR cannot borrow
+    borrow_mut(&mut *v); //~ ERROR cannot borrow
 }
 
 fn post_freeze() {
     // In this instance, the const alias starts after the borrow.
 
     let mut v = box 3;
-    borrow_mut(v);
+    borrow_mut(&mut *v);
     let _w = &v;
 }
 

src/test/compile-fail/lint-allocation.rs

@@ -11,9 +11,7 @@
 #![deny(unnecessary_allocation)]
 
 fn f(_: &int) {}
-fn g(_: &mut int) {}
 
 fn main() {
     f(box 1); //~ ERROR unnecessary allocation, use & instead
-    g(box 1); //~ ERROR unnecessary allocation, use &mut instead
 }

src/test/compile-fail/mut-cross-borrowing.rs

@@ -0,0 +1,17 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn f(_: &mut int) {}
+
+fn main() {
+    let mut x = box 3i;
+    f(x)    //~ ERROR mismatched types
+}
+

src/test/run-pass/borrowck-mut-uniq.rs

@@ -29,8 +29,8 @@ fn iter_ints(x: &Ints, f: |x: &int| -> bool) -> bool {
 
 pub fn main() {
     let mut ints = box Ints {sum: box 0, values: Vec::new()};
-    add_int(ints, 22);
-    add_int(ints, 44);
+    add_int(&mut *ints, 22);
+    add_int(&mut *ints, 44);
 
     iter_ints(ints, |i| {
         println!("int = {}", *i);