AST refactor: make the place in ExprBox an option.

This is to allow us to migrate away from UnUniq in a followup commit,
and thus unify the code paths related to all forms of `box`.

5 files changed, 8 insertions, 5 deletions

diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index 206fb26eb55..98d858babb1 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -696,7 +696,7 @@ pub struct Expr {
 #[deriving(Clone, PartialEq, Eq, Encodable, Decodable, Hash, Show)]
 pub enum Expr_ {
     /// First expr is the place; second expr is the value.
-    ExprBox(P<Expr>, P<Expr>),
+    ExprBox(Option<P<Expr>>, P<Expr>),
     ExprVec(Vec<P<Expr>>),
     ExprCall(P<Expr>, Vec<P<Expr>>),
     ExprMethodCall(SpannedIdent, Vec<P<Ty>>, Vec<P<Expr>>),
diff --git a/src/libsyntax/fold.rs b/src/libsyntax/fold.rs
index 8a578c2cb05..7d2acd08d94 100644
--- a/src/libsyntax/fold.rs
+++ b/src/libsyntax/fold.rs
@@ -1282,7 +1282,7 @@ pub fn noop_fold_expr<T: Folder>(Expr {id, node, span}: Expr, folder: &mut T) ->
         id: folder.new_id(id),
         node: match node {
             ExprBox(p, e) => {
-                ExprBox(folder.fold_expr(p), folder.fold_expr(e))
+                ExprBox(p.map(|e|folder.fold_expr(e)), folder.fold_expr(e))
             }
             ExprVec(exprs) => {
                 ExprVec(exprs.move_map(|x| folder.fold_expr(x)))
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index b9ef3fdbd49..6e3cfe5854a 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -2888,7 +2888,7 @@ impl<'a> Parser<'a> {
                     }
                     let subexpression = self.parse_prefix_expr();
                     hi = subexpression.span.hi;
-                    ex = ExprBox(place, subexpression);
+                    ex = ExprBox(Some(place), subexpression);
                     return self.mk_expr(lo, hi, ex);
                 }
             }
@@ -2896,6 +2896,9 @@ impl<'a> Parser<'a> {
             // Otherwise, we use the unique pointer default.
             let subexpression = self.parse_prefix_expr();
             hi = subexpression.span.hi;
+            // FIXME (pnkfelix): After working out kinks with box
+            // desugaring, should be `ExprBox(None, subexpression)`
+            // instead.
             ex = self.mk_unary(UnUniq, subexpression);
           }
           _ => return self.parse_dot_or_call_expr()
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index db122f271a9..4f45b69883b 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -1495,7 +1495,7 @@ impl<'a> State<'a> {
             ast::ExprBox(ref p, ref e) => {
                 try!(word(&mut self.s, "box"));
                 try!(word(&mut self.s, "("));
-                try!(self.print_expr(&**p));
+                try!(p.as_ref().map_or(Ok(()), |e|self.print_expr(&**e)));
                 try!(self.word_space(")"));
                 try!(self.print_expr(&**e));
             }
diff --git a/src/libsyntax/visit.rs b/src/libsyntax/visit.rs
index 3535c6e267e..f5a86bafea1 100644
--- a/src/libsyntax/visit.rs
+++ b/src/libsyntax/visit.rs
@@ -739,7 +739,7 @@ pub fn walk_mac<'v, V: Visitor<'v>>(_: &mut V, _: &'v Mac) {
 pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr) {
     match expression.node {
         ExprBox(ref place, ref subexpression) => {
-            visitor.visit_expr(&**place);
+            place.as_ref().map(|e|visitor.visit_expr(&**e));
             visitor.visit_expr(&**subexpression)
         }
         ExprVec(ref subexpressions) => {