dart2js: Extract minified field naming into mixin.

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
+  // the given element's class inheritance chain.
+  //
+  // The inheritance scope based naming might not yield a name. For instance,
+  // this could be because the field belongs to a mixin. In such a case this
+  // will return `null` and a normal field name has to be used.
+  jsAst.Name _minifiedInstanceFieldPropertyName(Element element) {
+    if (element.hasFixedBackendName) {
+      return new StringBackedName(element.fixedBackendName);
+    }
+
+    _FieldNamingScope names;
+    if (element is BoxFieldElement) {
+      names = new _FieldNamingScope.forBox(element.box, fieldRegistry);
+    } else {
+      ClassElement cls = element is ClosureFieldElement
+          ? element.closureClass
+          : element.enclosingClass;
+      names =
+          new _FieldNamingScope.forClass(cls, compiler.world, fieldRegistry);
+    }
+
+    if (names.containsField(element)) {
+      return names[element];
+    }
+    return null;
+  }
+}
+
+/**
+ * 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 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);
+      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));
+      }
+    }
+
+    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
+ * `Object` class. It is used to assign a unique name to each field of a class.
+ * Unique here means unique wrt. all fields along the path back to the root.
+ * This is achieved at construction time via the [_fieldNameCounter] field that
+ * counts the number of fields on the path to the root node that have been
+ * encountered so far.
+ *
+ * Obviously, this only works if no fields are added to a parent node after its
+ * children have added their first field.
+ */
+class _FieldNamingScope {
+  final _FieldNamingScope superScope;
+  final Entity container;
+  final Map<Element, jsAst.Name> names = new Maplet<Element, jsAst.Name>();
+  final _FieldNamingRegistry registry;
+
+  /// Naming counter used for fields of ordinary classes.
+  int _fieldNameCounter;
+
+  /// The number of fields along the superclass chain that use inheritance
+  /// based naming, including the ones allocated for this scope.
+  int get inheritanceBasedFieldNameCounter => _fieldNameCounter;
+
+  /// The number of locally used fields. Depending on the naming source
+  /// (e.g. inheritance based or globally unique for mixixns) this
+  /// might be different from [inheritanceBasedFieldNameCounter].
+  int get _localFieldNameCounter => _fieldNameCounter;
+  void set _localFieldNameCounter(int val) {
+    _fieldNameCounter = val;
+  }
+
+  factory _FieldNamingScope.forClass(
+      ClassElement cls, ClassWorld world, _FieldNamingRegistry registry) {
+    _FieldNamingScope result = registry.scopes[cls];
+    if (result != null) return result;
+
+    if (world.isUsedAsMixin(cls)) {
+      result = new _MixinFieldNamingScope.mixin(cls, registry);
+    } else {
+      if (cls.superclass == null) {
+        result = new _FieldNamingScope.rootScope(cls, registry);
+      } else {
+        _FieldNamingScope superScope =
+            new _FieldNamingScope.forClass(cls.superclass, world, registry);
+        if (cls.isMixinApplication) {
+          result =
+              new _MixinFieldNamingScope.mixedIn(cls, superScope, registry);
+        } else {
+          result = new _FieldNamingScope.inherit(cls, superScope, registry);
+        }
+      }
+    }
+
+    cls.forEachInstanceField((cls, field) => result.add(field));
+
+    registry.scopes[cls] = result;
+    return result;
+  }
+
+  factory _FieldNamingScope.forBox(Local box, _FieldNamingRegistry registry) {
+    return registry.scopes.putIfAbsent(
+        box, () => new _BoxFieldNamingScope(box, registry));
+  }
+
+  _FieldNamingScope.rootScope(this.container, this.registry)
+      : superScope = null,
+        _fieldNameCounter = 0;
+
+  _FieldNamingScope.inherit(this.container, this.superScope, this.registry) {
+    _fieldNameCounter = superScope.inheritanceBasedFieldNameCounter;
+  }
+
+  /**
+   * Checks whether [name] is already used in the current scope chain.
+   */
+  _isNameUnused(jsAst.Name name) {
+    return !names.values.contains(name) &&
+        ((superScope == null) || superScope._isNameUnused(name));
+  }
+
+  jsAst.Name _nextName() => registry.getName(_localFieldNameCounter++);
+
+  jsAst.Name operator [](Element field) {
+    jsAst.Name name = names[field];
+    if (name == null && superScope != null) return superScope[field];
+    return name;
+  }
+
+  void add(Element field) {
+    if (names.containsKey(field)) return;
+
+    jsAst.Name value = _nextName();
+    assert(invariant(field, _isNameUnused(value)));
+    names[field] = value;
+  }
+
+  bool containsField(Element field) => names.containsKey(field);
+}
+
+/**
+ * Field names for mixins have two constraints: They need to be unique in the
+ * hierarchy of each application of a mixin and they need to be the same for
+ * all applications of a mixin. To achieve this, we use global naming for
+ * mixins from the same name pool as fields and add a `$` at the end to ensure
+ * they do not collide with normal field names. The `$` sign is typically used
+ * as a separator between method names and argument counts and does not appear
+ * in generated names themselves.
+ */
+class _MixinFieldNamingScope extends _FieldNamingScope {
+  int get _localFieldNameCounter => registry.globalCount;
+  void set _localFieldNameCounter(int val) {
+    registry.globalCount = val;
+  }
+
+  @override
+  Map<Entity, jsAst.Name> get names => registry.globalNames;
+
+  _MixinFieldNamingScope.mixin(ClassElement cls, _FieldNamingRegistry registry)
+      : super.rootScope(cls, registry);
+
+  _MixinFieldNamingScope.mixedIn(MixinApplicationElement container,
+      _FieldNamingScope superScope, _FieldNamingRegistry registry)
+      : super.inherit(container, superScope, registry);
+
+  jsAst.Name _nextName() {
+    jsAst.Name proposed = super._nextName();
+    return new CompoundName([proposed, Namer._literalDollar]);
+  }
+}
+
+/**
+ * [BoxFieldElement] fields work differently in that they do not belong to an
+ * actual class but an anonymous box associated to a [Local]. As there is no
+ * inheritance chain, we do not need to compute fields a priori but can assign
+ * names on the fly.
+ */
+class _BoxFieldNamingScope extends _FieldNamingScope {
+  _BoxFieldNamingScope(Local box, _FieldNamingRegistry registry)
+      : super.rootScope(box, registry);
+
+  @override
+  bool containsField(_) => true;
+
+  jsAst.Name operator [](Element field) {
+    if (!names.containsKey(field)) add(field);
+    return names[field];
+  }
+}