Add hypothetical support for ranges with only an upper bound

Note that this doesn't add the surface syntax.

5 files changed, 7 insertions, 5 deletions

diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index d4932fbb5f1..e53e2cea1cc 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -724,7 +724,7 @@ pub enum Expr_ {
     ExprTupField(P<Expr>, Spanned<uint>),
     ExprIndex(P<Expr>, P<Expr>),
     ExprSlice(P<Expr>, Option<P<Expr>>, Option<P<Expr>>, Mutability),
-    ExprRange(P<Expr>, Option<P<Expr>>),
+    ExprRange(Option<P<Expr>>, Option<P<Expr>>),
 
     /// Variable reference, possibly containing `::` and/or
     /// type parameters, e.g. foo::bar::<baz>
diff --git a/src/libsyntax/fold.rs b/src/libsyntax/fold.rs
index c58901701f5..ede023c4e8b 100644
--- a/src/libsyntax/fold.rs
+++ b/src/libsyntax/fold.rs
@@ -1391,7 +1391,7 @@ pub fn noop_fold_expr<T: Folder>(Expr {id, node, span}: Expr, folder: &mut T) ->
                           m)
             }
             ExprRange(e1, e2) => {
-                ExprRange(folder.fold_expr(e1),
+                ExprRange(e1.map(|x| folder.fold_expr(x)),
                           e2.map(|x| folder.fold_expr(x)))
             }
             ExprPath(pth) => ExprPath(folder.fold_path(pth)),
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index a2e2abab03e..ec1e966926a 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -2144,7 +2144,7 @@ impl<'a> Parser<'a> {
                     start: P<Expr>,
                     end: Option<P<Expr>>)
                     -> ast::Expr_ {
-        ExprRange(start, end)
+        ExprRange(Some(start), end)
     }
 
     pub fn mk_field(&mut self, expr: P<Expr>, ident: ast::SpannedIdent) -> ast::Expr_ {
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index 623f20bccd2..a4b349c5f23 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -1760,7 +1760,9 @@ impl<'a> State<'a> {
                 try!(word(&mut self.s, "]"));
             }
             ast::ExprRange(ref start, ref end) => {
-                try!(self.print_expr(&**start));
+                if let &Some(ref e) = start {
+                    try!(self.print_expr(&**e));
+                }
                 try!(word(&mut self.s, ".."));
                 if let &Some(ref e) = end {
                     try!(self.print_expr(&**e));
diff --git a/src/libsyntax/visit.rs b/src/libsyntax/visit.rs
index 714339d0f0a..cde9ba932be 100644
--- a/src/libsyntax/visit.rs
+++ b/src/libsyntax/visit.rs
@@ -872,7 +872,7 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr) {
             walk_expr_opt(visitor, end)
         }
         ExprRange(ref start, ref end) => {
-            visitor.visit_expr(&**start);
+            walk_expr_opt(visitor, start);
             walk_expr_opt(visitor, end)
         }
         ExprPath(ref path) => {