Fix dangling else.

lib/compiler/implementation/js/printer.dart

Index: lib/compiler/implementation/js/printer.dart
diff --git a/lib/compiler/implementation/js/printer.dart b/lib/compiler/implementation/js/printer.dart
index 958435332dbbd31204916b45e24b56bc2a734eb7..b523ad823a8235f2086d715397328b40b937f36d 100644
--- a/lib/compiler/implementation/js/printer.dart
+++ b/lib/compiler/implementation/js/printer.dart
@@ -10,9 +10,12 @@ class Printer implements NodeVisitor {
   int indentLevel = 0;
   bool inForInit = false;
   bool atStatementBegin = false;
+  final DanglingElseVisitor danglingElseVisitor;
 
-  Printer(this.compiler, this.positionElement)
-      : outBuffer = new leg.CodeBuffer();
+  Printer(leg.Compiler compiler, this.positionElement)
+      : this.compiler = compiler,
+        outBuffer = new leg.CodeBuffer(),
+        danglingElseVisitor = new DanglingElseVisitor(compiler);
 
   void spaceOut() {
     if (!shouldCompressOutput) out(" ");
@@ -137,22 +140,13 @@ class Printer implements NodeVisitor {
     Node then = node.then;
     Node elsePart = node.otherwise;
     bool hasElse = node.hasElse;
+
     // Handle dangling elses.
-    // If the then-branch is an if, which has no else-branch, but we do
-    // have one, then we need to put the nested if into braces.
-    if (hasElse && then is If) {
-      Node nested = then;
-      do {
-        If nestedIf = nested;
-        if (!nestedIf.hasElse) {
-          then = new Block(<Statement>[then]);
-          break;
-        }
-        nested = nestedIf.otherwise;
-      } while (nested is If);
-    }
-    if (then is If && !(then as If).hasElse && hasElse) {
-      then = new Block(<Statement>[then]);
+    if (hasElse) {
+      bool needsBraces = node.then.accept(danglingElseVisitor);
+      if (needsBraces) {
+        then = new Block(<Statement>[then]);
+      }
     }
     if (shouldIndent) indent();
     out("if");
@@ -769,6 +763,56 @@ class Printer implements NodeVisitor {
   }
 }
 
+/**
+ * Returns true, if the given node must be wrapped into braces when used
+ * as then-statement in an [If] that has an else branch.
+ */
+class DanglingElseVisitor extends BaseVisitor<bool> {
+  leg.Compiler compiler;
+
+  DanglingElseVisitor(this.compiler);
+
+  bool visitProgram(Program node) => false;
+
+  bool visitNode(Statement node) {
+    compiler.internalError("Forgot node: $node");
+  }
+
+  bool visitBlock(Block node) => false;
+  bool visitExpressionStatement(ExpressionStatement node) => false;
+  bool visitEmptyStatement(EmptyStatement node) => false;
+  bool visitIf(If node) {
+    if (!node.hasElse) return true;
+    return node.otherwise.accept(this);
+  }
+  bool visitFor(For node) => node.body.accept(this);
+  bool visitForIn(ForIn node) => node.body.accept(this);
+  bool visitWhile(While node) => node.body.accept(this);
+  bool visitDo(Do node) => false;
+  bool visitContinue(Continue node) => false;
+  bool visitBreak(Break node) => false;
+  bool visitReturn(Return node) => false;
+  bool visitThrow(Throw node) => false;
+  bool visitTry(Try node) {
+    if (node.finallyPart != null) {
+      return node.finallyPart.accept(this);
+    } else {
+      return node.catchPart.accept(this);
+    }
+  }
+  bool visitCatch(Catch node) => node.body.accept(this);
+  bool visitSwitch(Switch node) => false;
+  bool visitCase(Case node) => false;
+  bool visitDefault(Default node) => false;
+  bool visitFunctionDeclaration(FunctionDeclaration node) => false;
+  bool visitLabeledStatement(LabeledStatement node)
+      => node.body.accept(this);
+  bool visitLiteralStatement(LiteralStatement node) => true;
+
+  bool visitExpression(Expression node) => false;
+}
+
+
 leg.CodeBuffer prettyPrint(Node node,
                            leg.Compiler compiler,
                            Dynamic positionElement) {