add optional scope parameter to TraversalPath#hoist

src/babel/traversal/path/hoister.js

@@ -12,6 +12,10 @@ var referenceVisitor = {
       if (this.isReferenced()) {
         var bindingInfo = scope.getBinding(node.name);
 
+        // this binding isn't accessible from the parent scope so we can safely ignore it
+        // eg. it's in a closure etc
+        if (bindingInfo !== state.scope.getBinding(node.name)) return;
+
         if (bindingInfo && bindingInfo.constant) {
           state.bindings[node.name] = bindingInfo;
         } else {
@@ -25,9 +29,10 @@ var referenceVisitor = {
 };
 
 export default class PathHoister {
-  constructor(path) {
+  constructor(path, scope) {
     this.foundIncompatible = false;
     this.bindings          = {};
+    this.scope             = scope;
     this.scopes            = [];
     this.path              = path;
   }

src/babel/traversal/path/index.js

@@ -644,8 +644,8 @@ export default class TraversalPath {
    * Description
    */
 
-  hoist() {
-    var hoister = new PathHoister(this);
+  hoist(scope = this.scope) {
+    var hoister = new PathHoister(this, scope);
     return hoister.run();
   }
 

src/babel/traversal/scope.js

@@ -75,6 +75,13 @@ export default class Scope {
       return parent;
     }
 
+    var cached = path.getData("scope");
+    if (cached && cached.parent === parent) {
+      return cached;
+    } else {
+      path.setData("scope", this);
+    }
+
     this.parent = parent;
     this.file   = parent ? parent.file : file;