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()) {
+    if (path.isFunction() && !first) {
-      return false;
+      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) {

test/core/fixtures/transformation/es6.tail-call/shadow/expected.js

@@ -2,12 +2,19 @@
 
 (function () {
   var _this = this,
-      _arguments = arguments;
+      _arguments2 = arguments;
 
   var foo = function foo() {
-    _this;
+    var _again = true;
-    _arguments;
+
-    foo();
+    _function: while (_again) {
+      _again = false;
+
+      _this;
+      _arguments2;
+      _again = true;
+      continue _function;
+    }
   };
   foo();
 });

test/core/fixtures/transformation/es6.tail-call/void/actual.js

@@ -0,0 +1,11 @@
+function skipWhile(cond) {
+  if (!hasNext() || cond(current, last)) return;
+  move();
+  skipWhile(cond);
+}
+
+var skipWhile2 = function (cond) {
+  if (!hasNext() || cond(current, last)) return;
+  move();
+  skipWhile2(cond);
+};

test/core/fixtures/transformation/es6.tail-call/void/expected.js

@@ -0,0 +1,31 @@
+"use strict";
+
+function skipWhile(_x) {
+  var _again = true;
+
+  _function: while (_again) {
+    var cond = _x;
+    _again = false;
+
+    if (!hasNext() || cond(current, last)) return;
+    move();
+    _x = cond;
+    _again = true;
+    continue _function;
+  }
+}
+
+var skipWhile2 = function skipWhile2(_x2) {
+  var _again2 = true;
+
+  _function2: while (_again2) {
+    var cond = _x2;
+    _again2 = false;
+
+    if (!hasNext() || cond(current, last)) return;
+    move();
+    _x2 = cond;
+    _again2 = true;
+    continue _function2;
+  }
+};