Merge branch 'optimize-with-a-split-visitor'

Author: eventualbuddha

lib/index.js

@@ -19,6 +19,11 @@ var util = require('ast-util');
  */
 function ArrowFunctionExpressionVisitor() {
   PathVisitor.call(this);
+
+  // In order to optimize the visitor we use a specific one for parsing the
+  // the body of the arrow function. This way very common types like Identifier
+  // are only visited under the subtree we're interested in.
+  this.bodyVisitor = new BodyVisitor(this);
 }
 ArrowFunctionExpressionVisitor.prototype = Object.create(PathVisitor.prototype);
 ArrowFunctionExpressionVisitor.prototype.constructor = ArrowFunctionExpressionVisitor;
@@ -30,7 +35,8 @@ ArrowFunctionExpressionVisitor.prototype.constructor = ArrowFunctionExpressionVi
  * @return {?Node}
  */
 ArrowFunctionExpressionVisitor.prototype.visitArrowFunctionExpression = function(path) {
-  this.traverse(path);
+  // Descend into the body using a specific visitor
+  this.traverse(path, this.bodyVisitor);
 
   var node = path.node;
   var hasThisExpression = ThisExpressionVisitor.hasThisExpression(node);
@@ -53,13 +59,29 @@ ArrowFunctionExpressionVisitor.prototype.visitArrowFunctionExpression = function
   }
 };
 
+/**
+ * Visits the body of an arrow function expressions.
+ *
+ * @constructor
+ * @private
+ * @extends PathVisitor
+ */
+function BodyVisitor(parent) {
+  // Support nested arrow function expressions by delegating on the parent visitor
+  this.visitArrowFunctionExpression = parent.visitArrowFunctionExpression;
+
+  PathVisitor.call(this);
+}
+BodyVisitor.prototype = Object.create(PathVisitor.prototype);
+BodyVisitor.prototype.constructor = BodyVisitor;
+
 /**
  * Ensures that `arguments` directly contained in arrow functions is hoisted.
  *
  * @param {types.NodePath} path
  * @return {?Node}
  */
-ArrowFunctionExpressionVisitor.prototype.visitIdentifier = function(path) {
+BodyVisitor.prototype.visitIdentifier = function(path) {
   var node = path.node;
 
   if (node.name === 'arguments' && util.isReference(path)) {
@@ -69,15 +91,15 @@ ArrowFunctionExpressionVisitor.prototype.visitIdentifier = function(path) {
     }
   }
 
-  this.traverse(path);
+  return false;  // nothing else to look at here
 };
 
 /**
  * @private
  * @param {types.NodePath} path
  * @return {?types.Scope} The nearest non-arrow function scope above `path`.
  */
-ArrowFunctionExpressionVisitor.prototype.associatedFunctionScope = function(path) {
+BodyVisitor.prototype.associatedFunctionScope = function(path) {
   var scope = path.scope;
   while (scope && n.ArrowFunctionExpression.check(scope.path.node)) {
     scope = scope.parent;