Support rest element pattern with user-defined iterable

test/mjsunit/harmony/destructuring-assignment.js

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Flags: --harmony-destructuring-assignment --harmony-destructuring-bind
 
 // script-level tests
 var ox, oy = {}, oz;
 ({
   x: ox,
@@ skipping 387 matching lines @@
     it = [g()];
     assertEquals(it, [ [...y] ] = it);
     assertEquals([undefined, undefined, undefined], y);
     assertEquals(6, count);
 
     it = { a: g() };
     assertEquals(it, { a: [...z] } = it);
     assertEquals([undefined, undefined, undefined], z);
     assertEquals(9, count);
   })();
+
+  (function cstm() {
+    var idx = 0;
+    var iterable = {};
+    var iterator = {
+      next: function() {
+        idx += 1;
+        return {
+          value: idx,
+          done: idx > 3
+        };
+      }
+    };
+    iterable[Symbol.iterator] = function() {
+      return iterator;
+    };
+    var result;
+
+    [...result] = iterable;
+
+    assertEquals([1, 2, 3], result);
+  })();
 })();
 
 (function testRequireObjectCoercible() {
   assertThrows(() => ({} = undefined), TypeError);
   assertThrows(() => ({} = null), TypeError);
   assertThrows(() => [] = undefined, TypeError);
   assertThrows(() => [] = null, TypeError);
   assertEquals("test", ({} = "test"));
   assertEquals("test", [] = "test");
   assertEquals(123, ({} = 123));
@@ skipping 55 matching lines @@
       assertEquals(["s", "p", "o", "r", "k"], x.rest);
       break;
     }
     log.push({ firstLetter: x.firstLetter, rest: x.rest });
   }
   assertEquals([
     { firstLetter: "\u{1F382}", rest: ["c", "a", "k", "e"] },
     { firstLetter: "B", rest: ["p", "u", "p", "p", "y"] },
   ], log);
 })();