Add representation for by-ref let bindings

Issue #918

src/comp/syntax/ast.rs

@@ -149,7 +149,9 @@ type local = spanned<local_>;
 
 type decl = spanned<decl_>;
 
-tag decl_ { decl_local([@local]); decl_item(@item); }
+tag let_style { let_copy; let_ref; }
+
+tag decl_ { decl_local([(let_style, @local)]); decl_item(@item); }
 
 type arm = {pats: [@pat], guard: option::t<@expr>, body: blk};
 

src/comp/syntax/fold.rs

@@ -296,7 +296,10 @@ fn noop_fold_pat(p: pat_, fld: ast_fold) -> pat_ {
 
 fn noop_fold_decl(d: decl_, fld: ast_fold) -> decl_ {
     ret alt d {
-          decl_local(ls) { decl_local(vec::map(fld.fold_local, ls)) }
+          decl_local(ls) {
+            decl_local(vec::map({|l| let (st, lc) = l;
+                                 (st, fld.fold_local(lc))}, ls))
+          }
           decl_item(it) { decl_item(fld.fold_item(it)) }
         }
 }

src/comp/syntax/parse/parser.rs

@@ -1505,11 +1505,13 @@ fn parse_local(p: parser, allow_init: bool) -> @ast::local {
 }
 
 fn parse_let(p: parser) -> @ast::decl {
+    fn parse_let_style(p: parser) -> ast::let_style {
+        eat(p, token::BINOP(token::AND)) ? ast::let_ref : ast::let_copy
+    }
     let lo = p.get_lo_pos();
-    let locals = [parse_local(p, true)];
-    while p.peek() == token::COMMA {
-        p.bump();
-        locals += [parse_local(p, true)];
+    let locals = [(parse_let_style(p), parse_local(p, true))];
+    while eat(p, token::COMMA) {
+        locals += [(parse_let_style(p), parse_local(p, true))];
     }
     ret @spanned(lo, p.get_last_hi_pos(), ast::decl_local(locals));
 }

src/comp/syntax/print/pprust.rs

@@ -1024,8 +1024,10 @@ fn print_decl(s: ps, decl: @ast::decl) {
         space_if_not_bol(s);
         ibox(s, indent_unit);
         word_nbsp(s, "let");
-        fn print_local(s: ps, loc: @ast::local) {
+        fn print_local(s: ps, loc_st: (ast::let_style, @ast::local)) {
+            let (st, loc) = loc_st;
             ibox(s, indent_unit);
+            if st == ast::let_ref { word(s.s, "&"); }
             print_local_decl(s, loc);
             end(s);
             alt loc.node.init {

src/comp/syntax/visit.rs

@@ -212,7 +212,7 @@ fn visit_stmt<E>(s: @stmt, e: E, v: vt<E>) {
 fn visit_decl<E>(d: @decl, e: E, v: vt<E>) {
     alt d.node {
       decl_local(locs) {
-        for loc: @ast::local in locs { v.visit_local(loc, e, v); }
+        for (_, loc) in locs { v.visit_local(loc, e, v); }
       }
       decl_item(it) { v.visit_item(it, e, v); }
     }