add support for tail calls when in completion record position - fixes #1572

src/babel/transformation/transformers/es6/tail-call.js

@@ -34,6 +34,12 @@ var visitor = {
     return state.subTransform(node.argument);
   },
 
+  ExpressionStatement(node, parent, scope, state) {
+    if (this.isCompletionRecord(true)) {
+      return state.subTransform(node.expression);
+    }
+  },
+
   Function() {
     this.skip();
   },

src/babel/traversal/path/verification.js

@@ -121,17 +121,20 @@ export function isPreviousType(type: string): boolean {
  * Check whether the current path references a completion record
  */
 
-export function isCompletionRecord() {
+export function isCompletionRecord(allowInsideFunction?) {
   var path = this;
+  var first = true;
 
   do {
     var container = path.container;
 
     // we're in a function so can't be a completion record
-    if (path.isFunctionDeclaration()) {
-      return false;
+    if (path.isFunction() && !first) {
+      return !!allowInsideFunction;
     }
 
+    first = false;
+
     // check to see if we're the last item in the container and if we are
     // we're a completion record!
     if (Array.isArray(container) && path.key !== container.length - 1) {