add checks needed for covariant generics, and List<E>

test/generated_sdk/lib/core/list.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart.core;
 
 /**
  * An indexable collection of objects with a length.
  *
  * Subclasses of this class implement different kinds of lists.
@@ skipping 59 matching lines @@
    *     growableList.length = 3;
    *
    * To create a growable list with a given length, just assign the length
    * right after creation:
    *
    *     List growableList = new List()..length = 500;
    *
    * The [length] must not be negative or null, if it is provided.
    */
   factory List([int length]) {
+    dynamic list;
     if (length == null) {
-      return JS('', '[]');
+      list = JS('', '[]');
+    } else {
+      // Explicit type test is necessary to guard against JavaScript conversions
+      // in unchecked mode.
+      if ((length is !int) || (length < 0)) {
+        throw new ArgumentError("Length must be a non-negative integer: $length");
+      }
+      list = JS('', 'new Array(#)', length);
+      // TODO(jmesserly): consider a fixed array subclass instead.
+      JS('void', r'#.fixed$length = Array', list);
     }
-    // Explicit type test is necessary to guard against JavaScript conversions
-    // in unchecked mode.
-    if ((length is !int) || (length < 0)) {
-      throw new ArgumentError("Length must be a non-negative integer: $length");
-    }
-    var list = JS('', 'new Array(#)', length);
-    // TODO(jmesserly): consider a fixed array subclass instead.
-    JS('void', r'#.fixed$length = Array', list);
+    // TODO(jmesserly): skip this when E is dynamic and Object.
+    JS('void', 'dart.setType(#, List\$(#))', list, E);
+    // TODO(jmesserly): compiler creates a bogus type check here.
     return list;
   }
 
   /**
    * Creates a fixed-length list of the given length, and initializes the
    * value at each position with [fill]:
    *
    *     new List<int>.filled(3, 0); // [0, 0, 0]
    *
    * The [length] must not be negative or null.
    */
   factory List.filled(int length, E fill) {
-    List result = new JSArray<E>.fixed(length);
+    List result = new List<E>(length);
     if (length != 0 && fill != null) {
       for (int i = 0; i < result.length; i++) {
         result[i] = fill;
       }
     }
     return result;
   }
 
   /**
    * Creates a list containing all [elements].
@@ skipping 627 matching lines @@
    *
    *     List<String> words = ['fee', 'fi', 'fo', 'fum'];
    *     Map<int, String> map = words.asMap();
    *     map[0] + map[1];   // 'feefi';
    *     map.keys.toList(); // [0, 1, 2, 3]
    */
   Map<int, E> asMap() {
     return new IterableMixinWorkaround<E>().asMapList(this);
   }
 }