librustc: Remove cross-borrowing of Box<T> to &T from the language,

except where trait objects are involved.

Part of issue rust-lang#15349, though I'm leaving it open for trait objects.
Cross borrowing for trait objects remains because it is needed until we
have DST.

This will break code like:

    fn foo(x: &int) { ... }

    let a = box 3i;
    foo(a);

Change this code to:

    fn foo(x: &int) { ... }

    let a = box 3i;
    foo(&*a);

[breaking-change]

Author: pcwalton

src/doc/guide-lifetimes.md

@@ -67,7 +67,7 @@ Now we can call `compute_distance()`:
 # let on_the_stack :     Point  =     Point{x: 3.0, y: 4.0};
 # let on_the_heap  : Box<Point> = box Point{x: 7.0, y: 9.0};
 # fn compute_distance(p1: &Point, p2: &Point) -> f64 { 0.0 }
-compute_distance(&on_the_stack, on_the_heap);
+compute_distance(&on_the_stack, &*on_the_heap);
 ~~~
 
 Here, the `&` operator takes the address of the variable
@@ -77,10 +77,9 @@ value. We also call this _borrowing_ the local variable
 `on_the_stack`, because we have created an alias: that is, another
 name for the same data.
 
-In the case of `on_the_heap`, however, no explicit action is necessary. 
-The compiler will automatically convert a box point to a reference like &point. 
-This is another form of borrowing; in this case, the contents of the owned box 
-are being lent out.
+Likewise, in the case of `owned_box`,
+the `&` operator is used in conjunction with the `*` operator
+to take a reference to the contents of the box.
 
 Whenever a caller lends data to a callee, there are some limitations on what
 the caller can do with the original. For example, if the contents of a

src/doc/guide-pointers.md

@@ -279,7 +279,7 @@ fn main() {
     let origin =    &Point { x: 0.0, y: 0.0 };
     let p1     = box Point { x: 5.0, y: 3.0 };
 
-    println!("{}", compute_distance(origin, p1));
+    println!("{}", compute_distance(origin, &*p1));
 }
 ~~~
 

src/doc/rust.md

@@ -3243,7 +3243,7 @@ enum List { Nil, Cons(uint, Box<List>) }
 fn is_sorted(list: &List) -> bool {
     match *list {
         Nil | Cons(_, box Nil) => true,
-        Cons(x, ref r @ box Cons(y, _)) => (x <= y) && is_sorted(*r)
+        Cons(x, ref r @ box Cons(y, _)) => (x <= y) && is_sorted(&**r)
     }
 }
 

src/doc/tutorial.md

@@ -1470,7 +1470,7 @@ Now we can call `compute_distance()` in various ways:
 # let on_the_stack :     Point  =     Point { x: 3.0, y: 4.0 };
 # let on_the_heap  : Box<Point> = box Point { x: 7.0, y: 9.0 };
 # fn compute_distance(p1: &Point, p2: &Point) -> f64 { 0.0 }
-compute_distance(&on_the_stack, on_the_heap);
+compute_distance(&on_the_stack, &*on_the_heap);
 ~~~
 
 Here the `&` operator is used to take the address of the variable
@@ -1480,11 +1480,9 @@ reference. We also call this _borrowing_ the local variable
 `on_the_stack`, because we are creating an alias: that is, another
 route to the same data.
 
-In the case of `owned_box`, however, no
-explicit action is necessary. The compiler will automatically convert
-a box `box point` to a reference like
-`&point`. This is another form of borrowing; in this case, the
-contents of the owned box are being lent out.
+Likewise, in the case of `owned_box`,
+the `&` operator is used in conjunction with the `*` operator
+to take a reference to the contents of the box.
 
 Whenever a value is borrowed, there are some limitations on what you
 can do with the original. For example, if the contents of a variable

src/liballoc/boxed.rs

@@ -67,7 +67,7 @@ impl<T:PartialEq> PartialEq for Box<T> {
 impl<T:PartialOrd> PartialOrd for Box<T> {
     #[inline]
     fn partial_cmp(&self, other: &Box<T>) -> Option<Ordering> {
-        (**self).partial_cmp(*other)
+        (**self).partial_cmp(&**other)
     }
     #[inline]
     fn lt(&self, other: &Box<T>) -> bool { *(*self) < *(*other) }
@@ -80,7 +80,9 @@ impl<T:PartialOrd> PartialOrd for Box<T> {
 }
 impl<T: Ord> Ord for Box<T> {
     #[inline]
-    fn cmp(&self, other: &Box<T>) -> Ordering { (**self).cmp(*other) }
+    fn cmp(&self, other: &Box<T>) -> Ordering {
+        (**self).cmp(&**other)
+    }
 }
 impl<T: Eq> Eq for Box<T> {}
 

src/libcollections/treemap.rs

@@ -516,7 +516,7 @@ define_iterator! {
 fn deref<'a, K, V>(node: &'a Option<Box<TreeNode<K, V>>>) -> *const TreeNode<K, V> {
     match *node {
         Some(ref n) => {
-            let n: &TreeNode<K, V> = *n;
+            let n: &TreeNode<K, V> = &**n;
             n as *const TreeNode<K, V>
         }
         None => ptr::null()

src/libregex_macros/lib.rs

@@ -623,15 +623,15 @@ fn parse(cx: &mut ExtCtxt, tts: &[ast::TokenTree]) -> Option<String> {
                 _ => {
                     cx.span_err(entry.span, format!(
                         "expected string literal but got `{}`",
-                        pprust::lit_to_string(lit)).as_slice());
+                        pprust::lit_to_string(&*lit)).as_slice());
                     return None
                 }
             }
         }
         _ => {
             cx.span_err(entry.span, format!(
                 "expected string literal but got `{}`",
-                pprust::expr_to_string(entry)).as_slice());
+                pprust::expr_to_string(&*entry)).as_slice());
             return None
         }
     };

src/librustc/driver/driver.rs

@@ -799,7 +799,7 @@ fn print_flowgraph<W:io::Writer>(variants: Vec<borrowck_dot::Variant>,
     let ty_cx = &analysis.ty_cx;
     let cfg = match code {
         blocks::BlockCode(block) => cfg::CFG::new(ty_cx, &*block),
-        blocks::FnLikeCode(fn_like) => cfg::CFG::new(ty_cx, fn_like.body()),
+        blocks::FnLikeCode(fn_like) => cfg::CFG::new(ty_cx, &*fn_like.body()),
     };
     debug!("cfg: {:?}", cfg);
 

src/librustc/metadata/encoder.rs

@@ -1248,7 +1248,7 @@ fn encode_info_for_item(ecx: &EncodeContext,
                     encode_method_sort(ebml_w, 'p');
                     encode_inlined_item(ecx, ebml_w,
                                         IIMethodRef(def_id, true, &*m));
-                    encode_method_argument_names(ebml_w, m.pe_fn_decl());
+                    encode_method_argument_names(ebml_w, &*m.pe_fn_decl());
                 }
             }
 

src/librustc/metadata/tyencode.rs

@@ -267,7 +267,7 @@ fn enc_sty(w: &mut MemWriter, cx: &ctxt, st: &ty::sty) {
         }
         ty::ty_closure(ref f) => {
             mywrite!(w, "f");
-            enc_closure_ty(w, cx, *f);
+            enc_closure_ty(w, cx, &**f);
         }
         ty::ty_bare_fn(ref f) => {
             mywrite!(w, "F");

src/librustc/middle/astencode.rs

@@ -1557,7 +1557,7 @@ fn test_simplification() {
             return alist {eq_fn: eq_int, data: Vec::new()};
         }
     ).unwrap();
-    let item_in = e::IIItemRef(item);
+    let item_in = e::IIItemRef(&*item);
     let item_out = simplify_ast(item_in);
     let item_exp = ast::IIItem(quote_item!(cx,
         fn new_int_alist<B>() -> alist<int, B> {
@@ -1566,7 +1566,8 @@ fn test_simplification() {
     ).unwrap());
     match (item_out, item_exp) {
       (ast::IIItem(item_out), ast::IIItem(item_exp)) => {
-        assert!(pprust::item_to_string(item_out) == pprust::item_to_string(item_exp));
+        assert!(pprust::item_to_string(&*item_out) ==
+                pprust::item_to_string(&*item_exp));
       }
       _ => fail!()
     }

src/librustc/middle/borrowck/mod.rs

@@ -216,8 +216,13 @@ pub fn build_borrowck_dataflow_data_for_fn<'a>(
 
     let p = input.fn_parts;
 
-    let dataflow_data = build_borrowck_dataflow_data(
-        &mut bccx, &p.kind, p.decl, input.cfg, p.body, p.span, p.id);
+    let dataflow_data = build_borrowck_dataflow_data(&mut bccx,
+                                                     &p.kind,
+                                                     &*p.decl,
+                                                     input.cfg,
+                                                     &*p.body,
+                                                     p.span,
+                                                     p.id);
 
     (bccx, dataflow_data)
 }

src/librustc/middle/check_match.rs

@@ -47,7 +47,9 @@ impl fmt::Show for Matrix {
 
         let &Matrix(ref m) = self;
         let pretty_printed_matrix: Vec<Vec<String>> = m.iter().map(|row| {
-            row.iter().map(|&pat| pat_to_string(pat)).collect::<Vec<String>>()
+            row.iter()
+               .map(|&pat| pat_to_string(&*pat))
+               .collect::<Vec<String>>()
         }).collect();
 
         let column_count = m.iter().map(|row| row.len()).max().unwrap_or(0u);

src/librustc/middle/dead.rs

@@ -212,7 +212,7 @@ impl<'a> MarkSymbolVisitor<'a> {
                 visit::walk_trait_method(self, &*trait_method, ctxt);
             }
             ast_map::NodeMethod(method) => {
-                visit::walk_block(self, method.pe_body(), ctxt);
+                visit::walk_block(self, &*method.pe_body(), ctxt);
             }
             ast_map::NodeForeignItem(foreign_item) => {
                 visit::walk_foreign_item(self, &*foreign_item, ctxt);
@@ -520,7 +520,9 @@ impl<'a> Visitor<()> for DeadVisitor<'a> {
     // Overwrite so that we don't warn the trait method itself.
     fn visit_trait_method(&mut self, trait_method: &ast::TraitMethod, _: ()) {
         match *trait_method {
-            ast::Provided(ref method) => visit::walk_block(self, method.pe_body(), ()),
+            ast::Provided(ref method) => {
+                visit::walk_block(self, &*method.pe_body(), ())
+            }
             ast::Required(_) => ()
         }
     }

src/librustc/middle/reachable.rs

@@ -316,14 +316,14 @@ impl<'a> ReachableContext<'a> {
                         // Keep going, nothing to get exported
                     }
                     ast::Provided(ref method) => {
-                        visit::walk_block(self, method.pe_body(), ())
+                        visit::walk_block(self, &*method.pe_body(), ())
                     }
                 }
             }
             ast_map::NodeMethod(method) => {
                 let did = self.tcx.map.get_parent_did(search_item);
                 if method_might_be_inlined(self.tcx, &*method, did) {
-                    visit::walk_block(self, method.pe_body(), ())
+                    visit::walk_block(self, &*method.pe_body(), ())
                 }
             }
             // Nothing to recurse on for these

src/librustc/middle/resolve.rs

@@ -3707,7 +3707,7 @@ impl<'a> Resolver<'a> {
 
                                 match ty_m.explicit_self.node {
                                     SelfExplicit(ref typ, _) => {
-                                        this.resolve_type(*typ)
+                                        this.resolve_type(&**typ)
                                     }
                                     _ => {}
                                 }
@@ -4044,7 +4044,7 @@ impl<'a> Resolver<'a> {
                                                 rib_kind);
 
         match method.pe_explicit_self().node {
-            SelfExplicit(ref typ, _) => self.resolve_type(*typ),
+            SelfExplicit(ref typ, _) => self.resolve_type(&**typ),
             _ => {}
         }
 

src/librustc/middle/save/mod.rs

@@ -356,9 +356,10 @@ impl <'l> DxrVisitor<'l> {
         for arg in method.pe_fn_decl().inputs.iter() {
             self.visit_ty(&*arg.ty, e);
         }
-        self.visit_ty(method.pe_fn_decl().output, e);
+        self.visit_ty(&*method.pe_fn_decl().output, e);
         // walk the fn body
-        self.visit_block(method.pe_body(), DxrVisitorEnv::new_nested(method.id));
+        self.visit_block(&*method.pe_body(),
+                         DxrVisitorEnv::new_nested(method.id));
 
         self.process_generic_params(method.pe_generics(),
                                     method.span,

src/librustc/middle/trans/_match.rs

@@ -491,7 +491,7 @@ fn enter_default<'a, 'b>(
 
     // Collect all of the matches that can match against anything.
     enter_match(bcx, dm, m, col, val, |pats| {
-        if pat_is_binding_or_wild(dm, pats[col]) {
+        if pat_is_binding_or_wild(dm, &*pats[col]) {
             Some(Vec::from_slice(pats.slice_to(col)).append(pats.slice_from(col + 1)))
         } else {
             None
@@ -546,8 +546,10 @@ fn enter_opt<'a, 'b>(
     let _indenter = indenter();
 
     let ctor = match opt {
-        &lit(x) => check_match::ConstantValue(const_eval::eval_const_expr(
-            bcx.tcx(), lit_to_expr(bcx.tcx(), &x))),
+        &lit(x) => {
+            check_match::ConstantValue(const_eval::eval_const_expr(
+                bcx.tcx(), &*lit_to_expr(bcx.tcx(), &x)))
+        }
         &range(ref lo, ref hi) => check_match::ConstantRange(
             const_eval::eval_const_expr(bcx.tcx(), &**lo),
             const_eval::eval_const_expr(bcx.tcx(), &**hi)

src/librustc/middle/trans/meth.rs

@@ -68,8 +68,13 @@ pub fn trans_impl(ccx: &CrateContext,
     for method in methods.iter() {
         if method.pe_generics().ty_params.len() == 0u {
             let llfn = get_item_val(ccx, method.id);
-            trans_fn(ccx, method.pe_fn_decl(), method.pe_body(),
-                     llfn, &param_substs::empty(), method.id, []);
+            trans_fn(ccx,
+                     &*method.pe_fn_decl(),
+                     &*method.pe_body(),
+                     llfn,
+                     &param_substs::empty(),
+                     method.id,
+                     []);
         } else {
             let mut v = TransItemVisitor{ ccx: ccx };
             visit::walk_method_helper(&mut v, &**method, ());

src/librustc/middle/ty.rs

@@ -2038,7 +2038,7 @@ pub fn type_contents(cx: &ctxt, ty: t) -> TypeContents {
             }
 
             ty_closure(ref c) => {
-                closure_contents(cx, *c)
+                closure_contents(cx, &**c)
             }
 
             ty_box(typ) => {

src/librustc/middle/typeck/astconv.rs

@@ -1018,7 +1018,7 @@ fn determine_explicit_self_category<AC:AstConv,
         }
         ast::SelfUniq(_) => ty::ByBoxExplicitSelfCategory,
         ast::SelfExplicit(ast_type, _) => {
-            let explicit_type = ast_ty_to_ty(this, rscope, ast_type);
+            let explicit_type = ast_ty_to_ty(this, rscope, &*ast_type);
 
             {
                 let inference_context = infer::new_infer_ctxt(this.tcx());

src/librustc/middle/typeck/check/mod.rs

@@ -764,7 +764,12 @@ fn check_method_body(ccx: &CrateCtxt,
 
     let fty = ty::node_id_to_type(ccx.tcx, method.id);
 
-    check_bare_fn(ccx, method.pe_fn_decl(), method.pe_body(), method.id, fty, param_env);
+    check_bare_fn(ccx,
+                  &*method.pe_fn_decl(),
+                  &*method.pe_body(),
+                  method.id,
+                  fty,
+                  param_env);
 }
 
 fn check_impl_methods_against_trait(ccx: &CrateCtxt,
@@ -2370,7 +2375,7 @@ fn check_expr_with_unifier(fcx: &FnCtxt,
 
         if ty::type_is_integral(lhs_t) && ast_util::is_shift_binop(op) {
             // Shift is a special case: rhs must be uint, no matter what lhs is
-            check_expr_has_type(fcx, rhs, ty::mk_uint());
+            check_expr_has_type(fcx, &*rhs, ty::mk_uint());
             fcx.write_ty(expr.id, lhs_t);
             return;
         }
@@ -2957,7 +2962,7 @@ fn check_expr_with_unifier(fcx: &FnCtxt,
       }
 
       ast::ExprLit(lit) => {
-        let typ = check_lit(fcx, lit, expected);
+        let typ = check_lit(fcx, &*lit, expected);
         fcx.write_ty(id, typ);
       }
       ast::ExprBinary(op, ref lhs, ref rhs) => {
@@ -3164,8 +3169,11 @@ fn check_expr_with_unifier(fcx: &FnCtxt,
         fcx.write_bot(id);
       }
       ast::ExprParen(a) => {
-        check_expr_with_expectation_and_lvalue_pref(fcx, a, expected, lvalue_pref);
-        fcx.write_ty(id, fcx.expr_ty(a));
+        check_expr_with_expectation_and_lvalue_pref(fcx,
+                                                    &*a,
+                                                    expected,
+                                                    lvalue_pref);
+        fcx.write_ty(id, fcx.expr_ty(&*a));
       }
       ast::ExprAssign(ref lhs, ref rhs) => {
         check_expr_with_lvalue_pref(fcx, &**lhs, PreferMutLvalue);
@@ -3326,8 +3334,8 @@ fn check_expr_with_unifier(fcx: &FnCtxt,
                 Some(ref fs) if i < fs.len() => ExpectHasType(*fs.get(i)),
                 _ => NoExpectation
             };
-            check_expr_with_expectation(fcx, *e, opt_hint);
-            let t = fcx.expr_ty(*e);
+            check_expr_with_expectation(fcx, &**e, opt_hint);
+            let t = fcx.expr_ty(&**e);
             err_field = err_field || ty::type_is_error(t);
             bot_field = bot_field || ty::type_is_bot(t);
             t
@@ -3674,8 +3682,8 @@ fn check_block_with_expected(fcx: &FnCtxt,
                              e.span,
                              "unreachable expression".to_string());
             }
-            check_expr_with_expectation(fcx, e, expected);
-              let ety = fcx.expr_ty(e);
+            check_expr_with_expectation(fcx, &*e, expected);
+              let ety = fcx.expr_ty(&*e);
               fcx.write_ty(blk.id, ety);
               if any_err {
                   fcx.write_error(blk.id);