auto merge of #11055 : pcwalton/rust/placement-box, r=pcwalton

r? @nikomatsakis 

5 files changed, 31 insertions, 1 deletions

diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index 2458577aa86..ef348e52f6e 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -547,6 +547,8 @@ pub enum CallSugar {
 #[deriving(Clone, Eq, Encodable, Decodable, IterBytes)]
 pub enum Expr_ {
     ExprVstore(@Expr, ExprVstore),
+    // First expr is the place; second expr is the value.
+    ExprBox(@Expr, @Expr),
     ExprVec(~[@Expr], Mutability),
     ExprCall(@Expr, ~[@Expr], CallSugar),
     ExprMethodCall(NodeId, @Expr, Ident, ~[P<Ty>], ~[@Expr], CallSugar),
diff --git a/src/libsyntax/fold.rs b/src/libsyntax/fold.rs
index c73edb0bfcf..409368ce3df 100644
--- a/src/libsyntax/fold.rs
+++ b/src/libsyntax/fold.rs
@@ -714,6 +714,9 @@ pub fn noop_fold_expr<T: Folder>(e: @Expr, folder: &mut T) -> @Expr {
         ExprVstore(e, v) => {
             ExprVstore(folder.fold_expr(e), v)
         }
+        ExprBox(p, e) => {
+            ExprBox(folder.fold_expr(p), folder.fold_expr(e))
+        }
         ExprVec(ref exprs, mutt) => {
             ExprVec(exprs.map(|&x| folder.fold_expr(x)), mutt)
         }
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index 149b7c1cf18..0424c71dd59 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -23,7 +23,7 @@ use ast::{BlockCheckMode, UnBox};
 use ast::{Crate, CrateConfig, Decl, DeclItem};
 use ast::{DeclLocal, DefaultBlock, UnDeref, BiDiv, EMPTY_CTXT, EnumDef, ExplicitSelf};
 use ast::{Expr, Expr_, ExprAddrOf, ExprMatch, ExprAgain};
-use ast::{ExprAssign, ExprAssignOp, ExprBinary, ExprBlock};
+use ast::{ExprAssign, ExprAssignOp, ExprBinary, ExprBlock, ExprBox};
 use ast::{ExprBreak, ExprCall, ExprCast, ExprDoBody};
 use ast::{ExprField, ExprFnBlock, ExprIf, ExprIndex};
 use ast::{ExprLit, ExprLogLevel, ExprLoop, ExprMac};
@@ -2321,6 +2321,20 @@ impl Parser {
           token::IDENT(_, _) if self.is_keyword(keywords::Box) => {
             self.bump();
 
+            // Check for a place: `box(PLACE) EXPR`.
+            if self.eat(&token::LPAREN) {
+                // Support `box() EXPR` as the default.
+                if !self.eat(&token::RPAREN) {
+                    let place = self.parse_expr();
+                    self.expect(&token::RPAREN);
+                    let subexpression = self.parse_prefix_expr();
+                    hi = subexpression.span.hi;
+                    ex = ExprBox(place, subexpression);
+                    return self.mk_expr(lo, hi, ex);
+                }
+            }
+
+            // Otherwise, we use the unique pointer default.
             let subexpression = self.parse_prefix_expr();
             hi = subexpression.span.hi;
             // HACK: turn `box [...]` into a boxed-evec
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index 1e2e5dbc010..ea9f0907b7a 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -1148,6 +1148,13 @@ pub fn print_expr(s: &mut State, expr: &ast::Expr) {
             print_expr_vstore(s, v);
             print_expr(s, e);
         },
+        ast::ExprBox(p, e) => {
+            word(&mut s.s, "box");
+            word(&mut s.s, "(");
+            print_expr(s, p);
+            word_space(s, ")");
+            print_expr(s, e);
+        }
       ast::ExprVec(ref exprs, mutbl) => {
         ibox(s, indent_unit);
         word(&mut s.s, "[");
diff --git a/src/libsyntax/visit.rs b/src/libsyntax/visit.rs
index 8e678a9bb73..1f0572a7785 100644
--- a/src/libsyntax/visit.rs
+++ b/src/libsyntax/visit.rs
@@ -614,6 +614,10 @@ pub fn walk_expr<E: Clone, V: Visitor<E>>(visitor: &mut V, expression: &Expr, en
         ExprVstore(subexpression, _) => {
             visitor.visit_expr(subexpression, env.clone())
         }
+        ExprBox(place, subexpression) => {
+            visitor.visit_expr(place, env.clone());
+            visitor.visit_expr(subexpression, env.clone())
+        }
         ExprVec(ref subexpressions, _) => {
             walk_exprs(visitor, *subexpressions, env.clone())
         }