handle "static" contexts in es7.functionBind - #1518

src/babel/transformation/transformers/es7/function-bind.js

@@ -10,11 +10,23 @@ export var metadata = {
 function getTempId(scope) {
   var id = scope.path.getData("functionBind");
   if (id) return id;
+
   id = scope.generateTemp("context");
   return scope.path.setData("functionBind", id);
 }
 
+function getStaticContext(bind, scope) {
+  if (bind.object) {
+    return scope.isStatic(bind.object) && bind.object;
+  } else {
+    return scope.isStatic(bind.callee.object) && bind.callee.object;
+  }
+}
+
 function inferBindContext(bind, scope) {
+  var staticContext = getStaticContext(bind, scope);
+  if (staticContext) return staticContext;
+
   var tempId = getTempId(scope);
   if (bind.object) {
     bind.callee = t.sequenceExpression([
@@ -30,6 +42,7 @@ function inferBindContext(bind, scope) {
 export function CallExpression(node, parent, scope, file) {
   var bind = node.callee;
   if (!t.isBindExpression(bind)) return;
+
   var context = inferBindContext(bind, scope);
   node.callee = t.memberExpression(bind.callee, t.identifier("call"));
   node.arguments.unshift(context);

src/babel/traversal/scope.js

@@ -263,18 +263,34 @@ export default class Scope {
     return this.generateUidIdentifier(id);
   }
 
+  /**
+   * Determine whether evaluating the specific input `node` is a consequenceless reference. ie.
+   * evaluating it wont result in potentially arbitrary code from being ran. The following are
+   * whitelisted and determined not cause side effects:
+   *
+   *  - `this` expressions
+   *  - `super` expressions
+   *  - Bound identifiers
+   */
+
+  isStatic(node: Object): boolean {
+    if (t.isThisExpression(node) || t.isSuper(node)) {
+      return true;
+    }
+
+    if (t.isIdentifier(node) && this.hasBinding(node.name)) {
+      return true;
+    }
+
+    return false;
+  }
+
   /**
    * Description
    */
 
   generateMemoisedReference(node: Object, dontPush?: boolean): ?Object {
-    if (t.isThisExpression(node) || t.isSuper(node)) {
-      return null;
-    }
-
-    if (t.isIdentifier(node) && this.hasBinding(node.name)) {
-      return null;
-    }
+    if (this.isStatic(node)) return null;
 
     var id = this.generateUidBasedOnNode(node);
     if (!dontPush) this.push({ id });