dart2js: Move field-visiting code to the program-builder.

pkg/compiler/lib/src/js_emitter/program_builder/field_visitor.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 dart2js.js_emitter.program_builder;
+
+/**
+ * [member] is a field (instance, static, or top level).
+ *
+ * [name] is the field name that the [Namer] has picked for this field's
+ * storage, that is, the JavaScript property name.
+ *
+ * [accessorName] is the name of the accessor. For instance fields this is
+ * mostly the same as [name] except when [member] is shadowing a field in its
+ * superclass.  For other fields, they are rarely the same.
+ *
+ * [needsGetter] and [needsSetter] represent if a getter or a setter
+ * respectively is needed.  There are many factors in this, for example, if the
+ * accessor can be inlined.
+ *
+ * [needsCheckedSetter] indicates that a checked getter is needed, and in this
+ * case, [needsSetter] is always false. [needsCheckedSetter] is only true when
+ * type assertions are enabled (checked mode).
+ */
+typedef void AcceptField(VariableElement member,
+                         js.Name name,
+                         js.Name accessorName,
+                         bool needsGetter,
+                         bool needsSetter,
+                         bool needsCheckedSetter);
+
+
+class FieldVisitor {
+  final Compiler compiler;
+  final Namer namer;
+
+  JavaScriptBackend get backend => compiler.backend;
+
+  FieldVisitor(this.compiler, this.namer);
+
+  /**
+   * Invokes [f] for each of the fields of [element].
+   *
+   * [element] must be a [ClassElement] or a [LibraryElement].
+   *
+   * If [element] is a [ClassElement], the static fields of the class are
+   * visited if [visitStatics] is true and the instance fields are visited if
+   * [visitStatics] is false.
+   *
+   * If [element] is a [LibraryElement], [visitStatics] must be true.
+   *
+   * When visiting the instance fields of a class, the fields of its superclass
+   * are also visited if the class is instantiated.
+   *
+   * Invariant: [element] must be a declaration element.
+   */
+  void visitFields(Element element, bool visitStatics, AcceptField f) {
+    assert(invariant(element, element.isDeclaration));
+
+    bool isClass = false;
+    bool isLibrary = false;
+    if (element.isClass) {
+      isClass = true;
+    } else if (element.isLibrary) {
+      isLibrary = true;
+      assert(invariant(element, visitStatics));
+    } else {
+      throw new SpannableAssertionFailure(
+          element, 'Expected a ClassElement or a LibraryElement.');
+    }
+
+    // If the class is never instantiated we still need to set it up for
+    // inheritance purposes, but we can simplify its JavaScript constructor.
+    bool isInstantiated =
+        compiler.codegenWorld.directlyInstantiatedClasses.contains(element);
+
+    void visitField(Element holder, FieldElement field) {
+      assert(invariant(element, field.isDeclaration));
+
+      // Keep track of whether or not we're dealing with a field mixin
+      // into a native class.
+      bool isMixinNativeField =
+          isClass && element.isNative && holder.isMixinApplication;
+
+      // See if we can dynamically create getters and setters.
+      // We can only generate getters and setters for [element] since
+      // the fields of super classes could be overwritten with getters or
+      // setters.
+      bool needsGetter = false;
+      bool needsSetter = false;
+      if (isLibrary || isMixinNativeField || holder == element) {
+        needsGetter = fieldNeedsGetter(field);
+        needsSetter = fieldNeedsSetter(field);
+      }
+
+      if ((isInstantiated && !holder.isNative)
+          || needsGetter
+          || needsSetter) {
+        js.Name accessorName = namer.fieldAccessorName(field);
+        js.Name fieldName = namer.fieldPropertyName(field);
+        bool needsCheckedSetter = false;
+        if (compiler.enableTypeAssertions
+            && needsSetter
+            && !canAvoidGeneratedCheckedSetter(field)) {
+          needsCheckedSetter = true;
+          needsSetter = false;
+        }
+        // Getters and setters with suffixes will be generated dynamically.
+        f(field, fieldName, accessorName, needsGetter, needsSetter,
+            needsCheckedSetter);
+      }
+    }
+
+    if (isLibrary) {
+      LibraryElement library = element;
+      library.implementation.forEachLocalMember((Element member) {
+        if (member.isField) visitField(library, member);
+      });
+    } else if (visitStatics) {
+      ClassElement cls = element;
+      cls.implementation.forEachStaticField(visitField);
+    } else {
+      ClassElement cls = element;
+      // TODO(kasperl): We should make sure to only emit one version of
+      // overridden fields. Right now, we rely on the ordering so the
+      // fields pulled in from mixins are replaced with the fields from
+      // the class definition.
+
+      // If a class is not instantiated then we add the field just so we can
+      // generate the field getter/setter dynamically. Since this is only
+      // allowed on fields that are in [element] we don't need to visit
+      // superclasses for non-instantiated classes.
+      cls.implementation.forEachInstanceField(
+          visitField, includeSuperAndInjectedMembers: isInstantiated);
+    }
+  }
+
+  bool fieldNeedsGetter(VariableElement field) {
+    assert(field.isField);
+    if (fieldAccessNeverThrows(field)) return false;
+    if (backend.shouldRetainGetter(field)) return true;
+    return field.isClassMember &&
+    compiler.codegenWorld.hasInvokedGetter(field, compiler.world);
+  }
+
+  bool fieldNeedsSetter(VariableElement field) {
+    assert(field.isField);
+    if (fieldAccessNeverThrows(field)) return false;
+    if (field.isFinal || field.isConst) return false;
+    if (backend.shouldRetainSetter(field)) return true;
+    return field.isClassMember &&
+    compiler.codegenWorld.hasInvokedSetter(field, compiler.world);
+  }
+
+  static bool fieldAccessNeverThrows(VariableElement field) {
+    return
+      // We never access a field in a closure (a captured variable) without
+      // knowing that it is there.  Therefore we don't need to use a getter
+      // (that will throw if the getter method is missing), but can always
+      // access the field directly.
+      field is ClosureFieldElement;
+  }
+
+  bool canAvoidGeneratedCheckedSetter(VariableElement member) {
+    // We never generate accessors for top-level/static fields.
+    if (!member.isInstanceMember) return true;
+    DartType type = member.type;
+    return type.treatAsDynamic || (type.element == compiler.objectClass);
+  }
+}