dart2js: use Es6 maps when available.

sdk/lib/_internal/compiler/js_lib/collection_patch.dart

Index: sdk/lib/_internal/compiler/js_lib/collection_patch.dart
diff --git a/sdk/lib/_internal/compiler/js_lib/collection_patch.dart b/sdk/lib/_internal/compiler/js_lib/collection_patch.dart
index 67e54bc0978c6367684ee3b35025e006361add9f..a1d3ba5eb073aec95dab121d0ba3f854d7946c12 100644
--- a/sdk/lib/_internal/compiler/js_lib/collection_patch.dart
+++ b/sdk/lib/_internal/compiler/js_lib/collection_patch.dart
@@ -5,7 +5,8 @@
 // Patch file for dart:collection classes.
 import 'dart:_foreign_helper' show JS;
 import 'dart:_js_helper' show
-    fillLiteralMap, InternalMap, NoInline, NoThrows, patch, JsLinkedHashMap,
+    fillLiteralMap, InternalMap, NoInline, NoThrows, patch,
+    JsLinkedHashMap, Es6LinkedHashMap,
     LinkedHashMapCell, LinkedHashMapKeyIterable, LinkedHashMapKeyIterator;
 
 @patch
@@ -386,6 +387,7 @@ class _CustomHashMap<K, V> extends _HashMap<K, V> {
   final _Equality<K> _equals;
   final _Hasher<K> _hashCode;
   final _Predicate _validKey;
+
   _CustomHashMap(this._equals, this._hashCode, bool validKey(potentialKey))
       : _validKey = (validKey != null) ? validKey : ((v) => v is K);
 
@@ -492,7 +494,11 @@ class LinkedHashMap<K, V> {
     if (isValidKey == null) {
       if (hashCode == null) {
         if (equals == null) {
-          return new JsLinkedHashMap<K, V>();
+          if (JsLinkedHashMap.supportsEs6Maps) {
+            return new Es6LinkedHashMap<K, V>();
+          } else {
+            return new JsLinkedHashMap<K, V>();
+          }
         }
         hashCode = _defaultHashCode;
       } else {
@@ -521,17 +527,24 @@ class LinkedHashMap<K, V> {
   // Private factory constructor called by generated code for map literals.
   @NoInline()
   factory LinkedHashMap._literal(List keyValuePairs) {
-    return fillLiteralMap(keyValuePairs, new JsLinkedHashMap<K, V>());
+    Map map = JsLinkedHashMap.supportsEs6Maps

[Vyacheslav Egorov (Google), 2015/03/26 00:03:57]

Can this just call some force-inline static method? cause seems like a bit of
duplication going on (there are three places with the same condition.

[Harry Terkelsen, 2015/03/26 00:40:06]

Won't that require generic methods?

[floitsch, 2015/03/26 00:53:24]

:)
I wondered the same, and had already started. The problem is, that functions
can't have generic types. So it would need to be a factory constructor.
That was my initial implementation (dispatching inside the JsLinkedHashMap
factory constructor). But that requires other changes all over the place,
because JsLinkedHashMap is subclassed.

One good alternative would be to create a named factory constructor in
JsLinkedHasMap. I just couldn't come up with a good name yet.

+        ? new Es6LinkedHashMap<K, V>()
+        : new JsLinkedHashMap<K, V>();
+    return fillLiteralMap(keyValuePairs, map);
   }
 
   // Private factory constructor called by generated code for map literals.
   @NoThrows() @NoInline()
   factory LinkedHashMap._empty() {
-    return new JsLinkedHashMap<K, V>();
+    return JsLinkedHashMap.supportsEs6Maps
+        ? new Es6LinkedHashMap<K, V>()
+        : new JsLinkedHashMap<K, V>();
   }
 }
 
+// TODO(floitsch): use ES6 Maps when available.
 class _LinkedIdentityHashMap<K, V> extends JsLinkedHashMap<K, V> {
+

[Harry Terkelsen, 2015/03/26 00:40:07]

unnecessary blank line

[floitsch, 2015/03/26 00:53:24]

Done.

   int internalComputeHashCode(var key) {
     // We force the hash codes to be unsigned 30-bit integers to avoid
     // issues with problematic keys like '__proto__'. Another option
@@ -550,14 +563,17 @@ class _LinkedIdentityHashMap<K, V> extends JsLinkedHashMap<K, V> {
   }
 }
 
+// TODO(floitsch): use ES6 maps when available.
 class _LinkedCustomHashMap<K, V> extends JsLinkedHashMap<K, V> {
   final _Equality<K> _equals;
   final _Hasher<K> _hashCode;
   final _Predicate _validKey;
+
   _LinkedCustomHashMap(this._equals, this._hashCode,
                        bool validKey(potentialKey))
       : _validKey = (validKey != null) ? validKey : ((v) => v is K);
 
+

[Harry Terkelsen, 2015/03/26 00:40:06]

unnecessary blank line

[floitsch, 2015/03/26 00:53:24]

Done.

   V operator[](Object key) {
     if (!_validKey(key)) return null;
     return super.internalGet(key);