unpack array rest elements when given a right hand array expression

lib/babel/transformation/transformers/es6/destructuring.js

@@ -163,13 +163,16 @@ var hasRest = function (pattern) {
 };
 
 DestructuringTransformer.prototype.canUnpackArrayPattern = function (pattern, arr) {
+  // not an array so there's no way we can deal with this
   if (!t.isArrayExpression(arr)) return false;
-  if (pattern.elements.length < arr.elements.length) return false;
 
+  // pattern has less elements than the array and doesn't have a rest so some
+  // elements wont be evaluated
+  if (pattern.elements.length < arr.elements.length && !hasRest(pattern)) return false;
+
+  // deopt on holes
   for (var i = 0; i < pattern.elements.length; i++) {
-    var elem = pattern.elements[i];
+    if (!pattern.elements[i]) return false;
-    if (!elem) return false; // hole
-    if (t.isRestElement(elem)) return false;
   }
 
   return true;
@@ -177,7 +180,12 @@ DestructuringTransformer.prototype.canUnpackArrayPattern = function (pattern, ar
 
 DestructuringTransformer.prototype.pushUnpackedArrayPattern = function (pattern, arr) {
   for (var i = 0; i < pattern.elements.length; i++) {
-    this.push(pattern.elements[i], arr.elements[i]);
+    var elem = pattern.elements[i]
+    if (t.isRestElement(elem)) {
+      this.push(elem.argument, t.arrayExpression(arr.elements.slice(i)));
+    } else {
+      this.push(elem, arr.elements[i]);
+    }
   }
 };
 

test/fixtures/transformation/es6-destructuring/array-unpack-optimisation/actual.js

@@ -1,9 +1,9 @@
 // opt
 var [a, b] = [1, 2];
 var [[a, b]] = [[1, 2]];
+var [a, b, ...c] = [1, 2, 3, 4];
+var [[a, b, ...c]] = [[1, 2, 3, 4]];
 
 // deopt
 var [a, b] = [1, 2, 3];
 var [[a, b]] = [[1, 2, 3]];
-var [a, b, ...items] = [1, 2, 3];
-var [[a, b, ...items]] = [[1, 2, 3]];

test/fixtures/transformation/es6-destructuring/array-unpack-optimisation/expected.js

@@ -5,6 +5,12 @@ var a = 1;
 var b = 2;
 var a = 1;
 var b = 2;
+var a = 1;
+var b = 2;
+var c = [3, 4];
+var a = 1;
+var b = 2;
+var c = [3, 4];
 
 // deopt
 var _ref = [1, 2, 3];
@@ -13,14 +19,3 @@ var b = _ref[1];
 var _ref2 = [1, 2, 3];
 var a = _ref2[0];
 var b = _ref2[1];
-var _ref3 = [1, 2, 3];
-var a = _ref3[0];
-var b = _ref3[1];
-
-var items = _ref3.slice(2);
-
-var _ref4 = [1, 2, 3];
-var a = _ref4[0];
-var b = _ref4[1];
-
-var items = _ref4.slice(2);