auto merge of #16102 : zwarich/rust/borrowck-unboxed, r=pcwalton

This removes the ability of the borrow checker to determine that repeated dereferences of a Box<T> refer to the same memory object.

Author: bors

src/libcollections/treemap.rs

@@ -1564,7 +1564,8 @@ fn remove<K: Ord, V>(node: &mut Option<Box<TreeNode<K, V>>>,
                 save.level -= 1;
 
                 if right_level > save.level {
-                    for x in save.right.mut_iter() { x.level = save.level }
+                    let save_level = save.level;
+                    for x in save.right.mut_iter() { x.level = save_level }
                 }
 
                 skew(save);

src/libcollections/trie.rs

@@ -783,7 +783,7 @@ fn insert<T>(count: &mut uint, child: &mut Child<T>, key: uint, value: T,
             *child = External(key, value);
             return None;
         }
-        Internal(ref mut x) => {
+        Internal(box ref mut x) => {
             return insert(&mut x.count, &mut x.children[chunk(key, idx)], key, value, idx + 1);
         }
         External(stored_key, ref mut stored_value) if stored_key == key => {
@@ -799,11 +799,17 @@ fn insert<T>(count: &mut uint, child: &mut Child<T>, key: uint, value: T,
     match mem::replace(child, Nothing) {
         External(stored_key, stored_value) => {
             let mut new = box TrieNode::new();
-            insert(&mut new.count,
-                   &mut new.children[chunk(stored_key, idx)],
-                   stored_key, stored_value, idx + 1);
-            let ret = insert(&mut new.count, &mut new.children[chunk(key, idx)],
-                         key, value, idx + 1);
+
+            let ret = {
+                let new_interior = &mut *new;
+                insert(&mut new_interior.count,
+                       &mut new_interior.children[chunk(stored_key, idx)],
+                       stored_key, stored_value, idx + 1);
+                insert(&mut new_interior.count,
+                       &mut new_interior.children[chunk(key, idx)],
+                       key, value, idx + 1)
+            };
+
             *child = Internal(new);
             return ret;
         }
@@ -821,7 +827,7 @@ fn remove<T>(count: &mut uint, child: &mut Child<T>, key: uint,
         }
       }
       External(..) => (None, false),
-      Internal(ref mut x) => {
+      Internal(box ref mut x) => {
           let ret = remove(&mut x.count, &mut x.children[chunk(key, idx)],
                            key, idx + 1);
           (ret, x.count == 0)

src/librustc/middle/borrowck/check_loans.rs

@@ -28,6 +28,57 @@ use util::ppaux::Repr;
 
 use std::rc::Rc;
 
+// FIXME (#16118): These functions are intended to allow the borrow checker to
+// be less precise in its handling of Box while still allowing moves out of a
+// Box. They should be removed when OwnedPtr is removed from LoanPath.
+
+fn owned_ptr_base_path<'a>(loan_path: &'a LoanPath) -> &'a LoanPath {
+    //! Returns the base of the leftmost dereference of an OwnedPtr in
+    //! `loan_path`. If there is no dereference of an OwnedPtr in `loan_path`,
+    //! then it just returns `loan_path` itself.
+
+    return match owned_ptr_base_path_helper(loan_path) {
+        Some(new_loan_path) => new_loan_path,
+        None => loan_path.clone()
+    };
+
+    fn owned_ptr_base_path_helper<'a>(loan_path: &'a LoanPath) -> Option<&'a LoanPath> {
+        match *loan_path {
+            LpVar(_) | LpUpvar(_) => None,
+            LpExtend(ref lp_base, _, LpDeref(mc::OwnedPtr)) => {
+                match owned_ptr_base_path_helper(&**lp_base) {
+                    v @ Some(_) => v,
+                    None => Some(&**lp_base)
+                }
+            }
+            LpExtend(ref lp_base, _, _) => owned_ptr_base_path_helper(&**lp_base)
+        }
+    }
+}
+
+fn owned_ptr_base_path_rc(loan_path: &Rc<LoanPath>) -> Rc<LoanPath> {
+    //! The equivalent of `owned_ptr_base_path` for an &Rc<LoanPath> rather than
+    //! a &LoanPath.
+
+    return match owned_ptr_base_path_helper(loan_path) {
+        Some(new_loan_path) => new_loan_path,
+        None => loan_path.clone()
+    };
+
+    fn owned_ptr_base_path_helper(loan_path: &Rc<LoanPath>) -> Option<Rc<LoanPath>> {
+        match **loan_path {
+            LpVar(_) | LpUpvar(_) => None,
+            LpExtend(ref lp_base, _, LpDeref(mc::OwnedPtr)) => {
+                match owned_ptr_base_path_helper(lp_base) {
+                    v @ Some(_) => v,
+                    None => Some(lp_base.clone())
+                }
+            }
+            LpExtend(ref lp_base, _, _) => owned_ptr_base_path_helper(lp_base)
+        }
+    }
+}
+
 struct CheckLoanCtxt<'a> {
     bccx: &'a BorrowckCtxt<'a>,
     dfcx_loans: &'a LoanDataFlow<'a>,
@@ -210,6 +261,7 @@ impl<'a> CheckLoanCtxt<'a> {
         //     let x = &mut a.b.c; // Restricts a, a.b, and a.b.c
         //     let y = a;          // Conflicts with restriction
 
+        let loan_path = owned_ptr_base_path(loan_path);
         let cont = self.each_in_scope_loan(scope_id, |loan| {
             let mut ret = true;
             for restr_path in loan.restricted_paths.iter() {
@@ -344,8 +396,9 @@ impl<'a> CheckLoanCtxt<'a> {
             return true;
         }
 
+        let loan2_base_path = owned_ptr_base_path_rc(&loan2.loan_path);
         for restr_path in loan1.restricted_paths.iter() {
-            if *restr_path != loan2.loan_path { continue; }
+            if *restr_path != loan2_base_path { continue; }
 
             let old_pronoun = if new_loan.loan_path == old_loan.loan_path {
                 "it".to_string()
@@ -597,7 +650,8 @@ impl<'a> CheckLoanCtxt<'a> {
 
         debug!("check_if_path_is_moved(id={:?}, use_kind={:?}, lp={})",
                id, use_kind, lp.repr(self.bccx.tcx));
-        self.move_data.each_move_of(id, lp, |move, moved_lp| {
+        let base_lp = owned_ptr_base_path_rc(lp);
+        self.move_data.each_move_of(id, &base_lp, |move, moved_lp| {
             self.bccx.report_use_of_moved_value(
                 span,
                 use_kind,

src/libstd/collections/lru_cache.rs

@@ -331,7 +331,8 @@ impl<K, V> Drop for LruCache<K, V> {
         unsafe {
             let node: Box<LruEntry<K, V>> = mem::transmute(self.head);
             // Prevent compiler from trying to drop the un-initialized field in the sigil node.
-            let box LruEntry { key: k, value: v, .. } = node;
+            let box internal_node = node;
+            let LruEntry { next: _, prev: _, key: k, value: v } = internal_node;
             mem::forget(k);
             mem::forget(v);
         }

src/test/compile-fail/borrowck-borrow-from-owned-ptr.rs

@@ -1,4 +1,4 @@
-// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
 // file at the top-level directory of this distribution and at
 // http://rust-lang.org/COPYRIGHT.
 //
@@ -52,14 +52,15 @@ fn borrow_same_field_twice_imm_imm() {
 fn borrow_both_fields_mut() {
     let mut foo = make_foo();
     let bar1 = &mut foo.bar1;
-    let _bar2 = &mut foo.bar2;
+    let _bar2 = &mut foo.bar2; //~ ERROR cannot borrow
     *bar1;
 }
 
 fn borrow_both_mut_pattern() {
     let mut foo = make_foo();
     match *foo {
         Foo { bar1: ref mut _bar1, bar2: ref mut _bar2 } => {}
+        //~^ ERROR cannot borrow
     }
 }
 
@@ -120,7 +121,7 @@ fn borrow_imm_and_base_imm() {
 fn borrow_mut_and_imm() {
     let mut foo = make_foo();
     let bar1 = &mut foo.bar1;
-    let _foo1 = &foo.bar2;
+    let _foo1 = &foo.bar2; //~ ERROR cannot borrow
     *bar1;
 }
 
@@ -133,7 +134,7 @@ fn borrow_mut_from_imm() {
 fn borrow_long_path_both_mut() {
     let mut foo = make_foo();
     let bar1 = &mut foo.bar1.int1;
-    let foo1 = &mut foo.bar2.int2;
+    let foo1 = &mut foo.bar2.int2; //~ ERROR cannot borrow
     *bar1;
     *foo1;
 }

src/test/compile-fail/borrowck-box-insensitivity.rs

@@ -0,0 +1,150 @@
+// Copyright 2014 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.
+
+struct A {
+    x: Box<int>,
+    y: int,
+}
+
+struct B {
+    x: Box<int>,
+    y: Box<int>,
+}
+
+struct C {
+    x: Box<A>,
+    y: int,
+}
+
+struct D {
+    x: Box<A>,
+    y: Box<int>,
+}
+
+fn copy_after_move() {
+    let a = box A { x: box 0, y: 1 };
+    let _x = a.x;
+    let _y = a.y; //~ ERROR use of partially moved
+}
+
+fn move_after_move() {
+    let a = box B { x: box 0, y: box 1 };
+    let _x = a.x;
+    let _y = a.y; //~ ERROR use of partially moved
+}
+
+fn borrow_after_move() {
+    let a = box A { x: box 0, y: 1 };
+    let _x = a.x;
+    let _y = &a.y; //~ ERROR use of partially moved
+}
+
+fn move_after_borrow() {
+    let a = box B { x: box 0, y: box 1 };
+    let _x = &a.x;
+    let _y = a.y; //~ ERROR cannot move
+}
+
+fn copy_after_mut_borrow() {
+    let mut a = box A { x: box 0, y: 1 };
+    let _x = &mut a.x;
+    let _y = a.y; //~ ERROR cannot use
+}
+
+fn move_after_mut_borrow() {
+    let mut a = box B { x: box 0, y: box 1 };
+    let _x = &mut a.x;
+    let _y = a.y; //~ ERROR cannot move
+}
+
+fn borrow_after_mut_borrow() {
+    let mut a = box A { x: box 0, y: 1 };
+    let _x = &mut a.x;
+    let _y = &a.y; //~ ERROR cannot borrow
+}
+
+fn mut_borrow_after_borrow() {
+    let mut a = box A { x: box 0, y: 1 };
+    let _x = &a.x;
+    let _y = &mut a.y; //~ ERROR cannot borrow
+}
+
+fn copy_after_move_nested() {
+    let a = box C { x: box A { x: box 0, y: 1 }, y: 2 };
+    let _x = a.x.x;
+    let _y = a.y; //~ ERROR use of partially moved
+}
+
+fn move_after_move_nested() {
+    let a = box D { x: box A { x: box 0, y: 1 }, y: box 2 };
+    let _x = a.x.x;
+    let _y = a.y; //~ ERROR use of partially moved
+}
+
+fn borrow_after_move_nested() {
+    let a = box C { x: box A { x: box 0, y: 1 }, y: 2 };
+    let _x = a.x.x;
+    let _y = &a.y; //~ ERROR use of partially moved
+}
+
+fn move_after_borrow_nested() {
+    let a = box D { x: box A { x: box 0, y: 1 }, y: box 2 };
+    let _x = &a.x.x;
+    let _y = a.y; //~ ERROR cannot move
+}
+
+fn copy_after_mut_borrow_nested() {
+    let mut a = box C { x: box A { x: box 0, y: 1 }, y: 2 };
+    let _x = &mut a.x.x;
+    let _y = a.y; //~ ERROR cannot use
+}
+
+fn move_after_mut_borrow_nested() {
+    let mut a = box D { x: box A { x: box 0, y: 1 }, y: box 2 };
+    let _x = &mut a.x.x;
+    let _y = a.y; //~ ERROR cannot move
+}
+
+fn borrow_after_mut_borrow_nested() {
+    let mut a = box C { x: box A { x: box 0, y: 1 }, y: 2 };
+    let _x = &mut a.x.x;
+    let _y = &a.y; //~ ERROR cannot borrow
+}
+
+fn mut_borrow_after_borrow_nested() {
+    let mut a = box C { x: box A { x: box 0, y: 1 }, y: 2 };
+    let _x = &a.x.x;
+    let _y = &mut a.y; //~ ERROR cannot borrow
+}
+
+fn main() {
+    copy_after_move();
+    move_after_move();
+    borrow_after_move();
+
+    move_after_borrow();
+
+    copy_after_mut_borrow();
+    move_after_mut_borrow();
+    borrow_after_mut_borrow();
+    mut_borrow_after_borrow();
+
+    copy_after_move_nested();
+    move_after_move_nested();
+    borrow_after_move_nested();
+
+    move_after_borrow_nested();
+
+    copy_after_mut_borrow_nested();
+    move_after_mut_borrow_nested();
+    borrow_after_mut_borrow_nested();
+    mut_borrow_after_borrow_nested();
+}
+

src/test/run-pass/match-implicit-copy-unique.rs

@@ -13,8 +13,9 @@ struct Pair { a: Box<int>, b: Box<int> }
 
 pub fn main() {
     let mut x = box Pair {a: box 10, b: box 20};
-    match x {
-      box Pair {a: ref mut a, b: ref mut _b} => {
+    let x_internal = &mut *x;
+    match *x_internal {
+      Pair {a: ref mut a, b: ref mut _b} => {
         assert!(**a == 10); *a = box 30; assert!(**a == 30);
       }
     }