add handling for loops when doing rest parameter allocation optimisation

packages/babel/src/transformation/transformers/es6/parameters/rest.js

@@ -223,7 +223,22 @@ export var visitor = {
     } else {
       // perform allocation at the lowest common denominator of all references
       loop._blockHoist = 1;
-      this.getEarliestCommonAncestorFrom(state.references).getStatementParent().insertBefore(loop);
+
+      var target = this.getEarliestCommonAncestorFrom(state.references).getStatementParent();
+
+      // don't perform the allocation inside a loop
+      var highestLoop;
+      target.findParent(function (path) {
+        if (path.isLoop()) {
+          highestLoop = path;
+        } else if (path.isFunction()) {
+          // stop crawling up for functions
+          return true;
+        }
+      });
+      if (highestLoop) target = highestLoop;
+
+      target.insertBefore(loop);
     }
   }
 };

packages/babel/test/fixtures/transformation/es6.parameters/rest-deepest-common-ancestor-earliest-child/actual.js

@@ -50,3 +50,19 @@ function a(...args) {
     console.log("Shouldn't args be from a's scope?", args);
   };
 }
+
+// loop
+function runQueue(queue, ...args) {
+  for (let i = 0; i < queue.length; i++) {
+    queue[i](...args)
+  }
+}
+
+// nested loop
+function runQueue(queue, ...args) {
+  if (foo) {
+    for (let i = 0; i < queue.length; i++) {
+      queue[i](...args)
+    }
+  }
+}

packages/babel/test/fixtures/transformation/es6.parameters/rest-deepest-common-ancestor-earliest-child/expected.js

@@ -77,3 +77,27 @@ function a() {
     console.log("Shouldn't args be from a's scope?", args);
   };
 }
+
+// loop
+function runQueue(queue) {
+  for (var _len = arguments.length, args = Array(_len > 1 ? _len - 1 : 0), _key = 1; _key < _len; _key++) {
+    args[_key - 1] = arguments[_key];
+  }
+
+  for (var i = 0; i < queue.length; i++) {
+    queue[i].apply(queue, args);
+  }
+}
+
+// nested loop
+function runQueue(queue) {
+  if (foo) {
+    for (var _len = arguments.length, args = Array(_len > 1 ? _len - 1 : 0), _key = 1; _key < _len; _key++) {
+      args[_key - 1] = arguments[_key];
+    }
+
+    for (var i = 0; i < queue.length; i++) {
+      queue[i].apply(queue, args);
+    }
+  }
+}