more intelligent parens wrapping of no line terminator expressions - fixes #376, reference #349

lib/6to5/generation/generator.js

@@ -148,11 +148,11 @@ CodeGenerator.prototype.print = function (node, parent, opts) {
   };
 
   if (this[node.type]) {
-    var needsCommentParens = t.isExpression(node) && node.leadingComments && node.leadingComments.length;
-    var needsParens        = needsCommentParens || n.needsParens(node, parent);
+    var needsNoLineTermParens = n.needsParensNoLineTerminator(node, parent);
+    var needsParens           = needsNoLineTermParens || n.needsParens(node, parent);
 
     if (needsParens) this.push("(");
-    if (needsCommentParens) this.indent();
+    if (needsNoLineTermParens) this.indent();
 
     this.printLeadingComments(node, parent);
 
@@ -163,7 +163,7 @@ CodeGenerator.prototype.print = function (node, parent, opts) {
 
     this[node.type](node, this.buildPrint(node), parent);
 
-    if (needsCommentParens) {
+    if (needsNoLineTermParens) {
       this.newline();
       this.dedent();
     }

lib/6to5/generation/node/index.js

@@ -69,6 +69,29 @@ Node.prototype.needsParens = function () {
   return find(parens, node, parent);
 };
 
+Node.prototype.needsParensNoLineTerminator = function () {
+  var parent = this.parent;
+  var node   = this.node;
+
+  if (!parent) return false;
+
+  // no comments
+  if (!node.leadingComments || !node.leadingComments.length) {
+    return false;
+  }
+
+  if (t.isYieldExpression(parent) || t.isAwaitExpression(parent)) {
+    return true;
+  }
+
+  if (t.isContinueStatement(parent) || t.isBreakStatement(parent) ||
+      t.isReturnStatement(parent) || t.isThrowStatement(parent)) {
+    return true;
+  }
+
+  return false;
+};
+
 _.each(Node.prototype, function (fn, key) {
   Node[key] = function (node, parent) {
     var n = new Node(node, parent);

lib/6to5/generation/node/parentheses.js

@@ -20,6 +20,20 @@ _.each([
   });
 });
 
+exports.ObjectExpression = function (node, parent) {
+  if (t.isExpressionStatement(parent)) {
+    // ({ foo: "bar" });
+    return true;
+  }
+
+  if (t.isMemberExpression(parent) && parent.object === node) {
+    // ({ foo: "bar" }).foo
+    return true;
+  }
+
+  return false;
+};
+
 exports.Binary = function (node, parent) {
   if (t.isCallExpression(parent) && parent.callee === node) {
     return true;