Teach rustc to parse 'else if'

Author: brson

src/Makefile

@@ -447,6 +447,7 @@ TEST_XFAILS_RUSTC := $(filter-out \
                         div-mod.rs \
                         drop-bind-thunk-args.rs \
                         drop-on-ret.rs \
+                        else-if.rs \
                         fact.rs \
                         fn-lval.rs \
                         fun-call-variants.rs \

src/comp/front/parser.rs

@@ -895,8 +895,7 @@ impure fn parse_if_expr(parser p) -> @ast.expr {
     hi = thn.span;
     alt (p.peek()) {
         case (token.ELSE) {
-            p.bump();
-            auto eblk = parse_block(p);
+            auto eblk = parse_else_block(p);
             els = some(eblk);
             hi = eblk.span;
         }
@@ -905,6 +904,21 @@ impure fn parse_if_expr(parser p) -> @ast.expr {
     ret @spanned(lo, hi, ast.expr_if(cond, thn, els, ast.ann_none));
 }
 
+impure fn parse_else_block(parser p) -> ast.block {
+    expect(p, token.ELSE);
+    alt (p.peek()) {
+        case (token.IF) {
+            let vec[@ast.stmt] stmts = vec();
+            auto ifexpr = parse_if_expr(p);
+            auto bloc = index_block(stmts, some(ifexpr));
+            ret spanned(ifexpr.span, ifexpr.span, bloc);
+        }
+        case (_) {
+            ret parse_block(p);
+        }
+    }
+}
+
 impure fn parse_head_local(parser p) -> @ast.decl {
     auto lo = p.get_span();
     let @ast.local local;