vaoid being greedy when destructuring array iterables

lib/6to5/file.js

@@ -22,6 +22,7 @@ File.declarations = [
   "tagged-template-literal",
   "interop-require",
   "to-array",
+  "sliced-to-array",
   "object-without-properties",
   "has-own",
   "slice"
@@ -82,13 +83,19 @@ File.normaliseOptions = function (opts) {
   return opts;
 };
 
-File.prototype.toArray = function (node) {
+File.prototype.toArray = function (node, i) {
   if (t.isArrayExpression(node)) {
     return node;
   } else if (t.isIdentifier(node) && node.name === "arguments") {
     return t.callExpression(t.memberExpression(this.addDeclaration("slice"), t.identifier("call")), [node]);
   } else {
-    return t.callExpression(this.addDeclaration("to-array"), [node]);
+    var declarationName = "to-array";
+    var args = [node];
+    if (i) {
+      args.push(t.literal(i));
+      declarationName = "sliced-to-array";
+    }
+    return t.callExpression(this.addDeclaration(declarationName), args);
   }
 };
 

lib/6to5/templates/sliced-to-array.js

@@ -0,0 +1,12 @@
+(function (arr, i) {
+  if (Array.isArray(arr)) {
+    return arr;
+  } else {
+    var _arr = [];
+    for (var _iterator = arr[Symbol.iterator](), _step; !(_step = _iterator.next()).done;) {
+      _arr.push(_step.value);
+      if (i && _arr.length === i) break;
+    }
+    return _arr;
+  }
+});

lib/6to5/transformation/transformers/es6-destructuring.js

@@ -1,6 +1,7 @@
 // TODO: Clean up
 
 var t = require("../../types");
+var _ = require("lodash");
 
 var buildVariableAssign = function (opts, id, init) {
   var op = opts.operator;
@@ -61,9 +62,21 @@ var pushObjectPattern = function (opts, nodes, pattern, parentId) {
 };
 
 var pushArrayPattern = function (opts, nodes, pattern, parentId) {
+  if (!pattern.elements) return;
+
+  var hasSpreadElement = false;
+  for (var i in pattern.elements) {
+    if (t.isSpreadElement(pattern.elements[i])) {
+      hasSpreadElement = true;
+      break;
+    }
+  }
+
+  var toArray = opts.file.toArray(parentId, !hasSpreadElement && pattern.elements.length);
+
   var _parentId = opts.file.generateUidIdentifier("ref", opts.scope);
   nodes.push(t.variableDeclaration("var", [
-    t.variableDeclarator(_parentId, opts.file.toArray(parentId))
+    t.variableDeclarator(_parentId, toArray)
   ]));
   parentId = _parentId;