Use WeakMap to support Expando if available.

Retains the existing code as fallback for settings without WeakMap for now.

Fixes issue #5144

BUG= http://dartbug.com/5144
[email protected]

Review URL: https://codereview.chromium.org/1599393003 .

Author: lrhn

runtime/lib/expando_patch.dart

@@ -131,7 +131,8 @@ patch class Expando<T> {
          (object is bool) ||
          (object is num) ||
          (object is String)) {
-      throw new ArgumentError(object);
+      throw new ArgumentError.value(object,
+          "Expandos are not allowed on strings, numbers, booleans or null");
     }
   }
 

sdk/lib/_internal/js_runtime/lib/core_patch.dart

@@ -106,37 +106,61 @@ class Function {
 // Patch for Expando implementation.
 @patch
 class Expando<T> {
+  static const String _EXPANDO_PROPERTY_NAME = 'expando\$values';
+
+  // Incremented to make unique keys.
+  static int _keyCount = 0;
+
+  // Stores either a JS WeakMap or a "unique" string key.
+  final Object _jsWeakMapOrKey;
+
   @patch
-  Expando([String name]) : this.name = name;
+  Expando([String name])
+      : this.name = name,
+        _jsWeakMapOrKey = JS('bool', 'typeof WeakMap == "function"')
+            ? JS('=Object|Null', 'new WeakMap()')
+            : _createKey();
 
   @patch
   T operator[](Object object) {
-    var values = Primitives.getProperty(object, _EXPANDO_PROPERTY_NAME);
-    return (values == null) ? null : Primitives.getProperty(values, _getKey());
+    if (_jsWeakMapOrKey is! String) {
+      _checkType(object);  // WeakMap doesn't check on reading, only writing.
+      return JS('', '#.get(#)', _jsWeakMapOrKey, object);
+    }
+    return _getFromObject(_jsWeakMapOrKey, object);
   }
 
   @patch
   void operator[]=(Object object, T value) {
+    if (_jsWeakMapOrKey is! String) {
+      JS('void', '#.set(#, #)', _jsWeakMapOrKey, object, value);
+    } else {
+      _setOnObject(_jsWeakMapOrKey, object, value);
+    }
+  }
+
+  static Object _getFromObject(String key, Object object) {
+    var values = Primitives.getProperty(object, _EXPANDO_PROPERTY_NAME);
+    return (values == null) ? null : Primitives.getProperty(values, key);
+  }
+
+  static void _setOnObject(String key, Object object, Object value) {
     var values = Primitives.getProperty(object, _EXPANDO_PROPERTY_NAME);
     if (values == null) {
       values = new Object();
       Primitives.setProperty(object, _EXPANDO_PROPERTY_NAME, values);
     }
-    Primitives.setProperty(values, _getKey(), value);
+    Primitives.setProperty(values, key, value);
   }
 
-  String _getKey() {
-    String key = Primitives.getProperty(this, _KEY_PROPERTY_NAME);
-    if (key == null) {
-      key = "expando\$key\$${_keyCount++}";
-      Primitives.setProperty(this, _KEY_PROPERTY_NAME, key);
+  static String _createKey() => "expando\$key\$${_keyCount++}";
+
+  static _checkType(object) {
+    if (object == null || object is bool || object is num || object is String) {
+      throw new ArgumentError.value(object,
+          "Expandos are not allowed on strings, numbers, booleans or null");
     }
-    return key;
   }
-
-  static const String _KEY_PROPERTY_NAME = 'expando\$key';
-  static const String _EXPANDO_PROPERTY_NAME = 'expando\$values';
-  static int _keyCount = 0;
 }
 
 @patch

tests/corelib/expando_test.dart

@@ -18,7 +18,7 @@ class ExpandoTest {
       testUnnamedExpando(object);
     }
     for (var object in legal) {
-      Expect.equals(2, visits[object]);
+      Expect.equals(2, visits[object], "$object");
     }
     testIllegal();
     testIdentity();
@@ -65,19 +65,19 @@ class ExpandoTest {
   static testIllegal() {
     Expando<int> expando = new Expando<int>();
     Expect.throws(() => expando[null], (exception)
-                  => exception is ArgumentError);
+                  => exception is ArgumentError, "null");
     Expect.throws(() => expando['string'], (exception)
-                  => exception is ArgumentError);
+                  => exception is ArgumentError, "'string'");
     Expect.throws(() => expando['string'], (exception)
-                  => exception is ArgumentError);
+                  => exception is ArgumentError, "'string'");
     Expect.throws(() => expando[42], (exception)
-                  => exception is ArgumentError);
+                  => exception is ArgumentError, "42");
     Expect.throws(() => expando[42.87], (exception)
-                  => exception is ArgumentError);
+                  => exception is ArgumentError, "42.87");
     Expect.throws(() => expando[true], (exception)
-                  => exception is ArgumentError);
+                  => exception is ArgumentError, "true");
     Expect.throws(() => expando[false], (exception)
-                  => exception is ArgumentError);
+                  => exception is ArgumentError, "false");
   }
 
   static testIdentity() {