dart2js: Implement frequency based naming.

pkg/compiler/lib/src/js_backend/field_naming_mixin.dart

 // Copyright (c) 2015, 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 js_backend;
 
 abstract class _MinifiedFieldNamer implements Namer {
   _FieldNamingRegistry get fieldRegistry;
 
   // Returns a minimal name for the field that is globally unique along
@@ skipping 26 matching lines @@
 }
 
 /**
  * Encapsulates the global state of field naming.
  *
  * The field naming registry allocates names to be used along a path in the
  * inheritance hierarchy of fields, starting with the object class. The actual
  * hierarchy is encoded using instances of [_FieldNamingScope].
  */
 class _FieldNamingRegistry {
-  final MinifyNamer namer;
+  final Namer namer;
 
   final Map<Entity, _FieldNamingScope> scopes =
       new Map<Entity, _FieldNamingScope>();
 
   final Map<Entity, jsAst.Name> globalNames = new Map<Entity, jsAst.Name>();
 
   int globalCount = 0;
 
   final List<jsAst.Name> nameStore = new List<jsAst.Name>();
 
   _FieldNamingRegistry(this.namer);
 
   // Returns the name to be used for a field with distance [index] from the
   // root of the object hierarchy. The distance thereby is computed as the
   // number of fields preceding the current field in its classes inheritance
   // chain.
   //
   // The implementation assumes that names are requedsted in order, that is the
   // name at position i+1 is requested after the name at position i was
   // requested.
   jsAst.Name getName(int index) {
     if (index >= nameStore.length) {
       // The namer usually does not use certain names as they clash with
       // existing properties on JS objects (see [_reservedNativeProperties]).
       // However, some of them are really short and safe to use for fields.
       // Thus, we shortcut the namer to use those first.
-      assert(index == nameStore.length + 1);
+      assert(index == nameStore.length);

[herhut, 2015/06/30 16:33:26]

this is a back-ported fix from a later revision...

       if (index < MinifyNamer._reservedNativeProperties.length &&
           MinifyNamer._reservedNativeProperties[index].length <= 2) {
         nameStore.add(
             new StringBackedName(MinifyNamer._reservedNativeProperties[index]));
       } else {
-        nameStore.add(namer.getFreshName("field$index", namer.usedInstanceNames,
-            namer.suggestedInstanceNames));
+        nameStore.add(namer.getFreshName(NamingScope.instance, "field$index"));
       }
     }
 
     return nameStore[index];
   }
 }
 
 /**
  * A [_FieldNamingScope] encodes a node in the inheritance tree of the current
  * class hierarchy. The root node typically is the node corresponding to the
@@ skipping 137 matching lines @@
       : super.rootScope(box, registry);
 
   @override
   bool containsField(_) => true;
 
   jsAst.Name operator [](Element field) {
     if (!names.containsKey(field)) add(field);
     return names[field];
   }
 }