Move scopes into a separate library

pkg/analyzer/lib/src/dart/resolver/scope.dart

+// Copyright (c) 2014, 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.
+
+library analyzer.src.dart.resolver.scope;
+
+import 'dart:collection';
+
+import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/element/element.dart';
+import 'package:analyzer/src/dart/element/element.dart';
+import 'package:analyzer/src/generated/engine.dart';
+import 'package:analyzer/src/generated/error.dart';
+import 'package:analyzer/src/generated/java_core.dart';
+import 'package:analyzer/src/generated/java_engine.dart';
+import 'package:analyzer/src/generated/source.dart';
+
+/**
+ * The scope defined by a class.
+ */
+class ClassScope extends EnclosedScope {
+  /**
+   * Initialize a newly created scope, enclosed within the [enclosingScope],
+   * based on the given [classElement].
+   */
+  ClassScope(Scope enclosingScope, ClassElement classElement)
+      : super(enclosingScope) {
+    if (classElement == null) {
+      throw new IllegalArgumentException("class element cannot be null");
+    }
+    _defineMembers(classElement);
+  }
+
+  @override
+  AnalysisError getErrorForDuplicate(Element existing, Element duplicate) {
+    if (existing is PropertyAccessorElement && duplicate is MethodElement) {
+      if (existing.nameOffset < duplicate.nameOffset) {
+        return new AnalysisError(
+            duplicate.source,
+            duplicate.nameOffset,
+            duplicate.nameLength,
+            CompileTimeErrorCode.METHOD_AND_GETTER_WITH_SAME_NAME,
+            [existing.displayName]);
+      } else {
+        return new AnalysisError(
+            existing.source,
+            existing.nameOffset,
+            existing.nameLength,
+            CompileTimeErrorCode.GETTER_AND_METHOD_WITH_SAME_NAME,
+            [existing.displayName]);
+      }
+    }
+    return super.getErrorForDuplicate(existing, duplicate);
+  }
+
+  /**
+   * Define the instance members defined by the given [classElement].
+   */
+  void _defineMembers(ClassElement classElement) {
+    for (PropertyAccessorElement accessor in classElement.accessors) {
+      define(accessor);
+    }
+    for (MethodElement method in classElement.methods) {
+      define(method);
+    }
+  }
+}
+
+/**
+ * A scope that is lexically enclosed in another scope.
+ */
+class EnclosedScope extends Scope {
+  /**
+   * The scope in which this scope is lexically enclosed.
+   */
+  @override
+  final Scope enclosingScope;
+
+  /**
+   * A table mapping names that will be defined in this scope, but right now are
+   * not initialized. According to the scoping rules these names are hidden,
+   * even if they were defined in an outer scope.
+   */
+  HashMap<String, Element> _hiddenElements = new HashMap<String, Element>();
+
+  /**
+   * A flag indicating whether there are any names hidden in this scope.
+   */
+  bool _hasHiddenName = false;
+
+  /**
+   * Initialize a newly created scope, enclosed within the [enclosingScope].
+   */
+  EnclosedScope(this.enclosingScope);
+
+  @override
+  AnalysisErrorListener get errorListener => enclosingScope.errorListener;
+
+  /**
+   * Record that given [element] is declared in this scope, but hasn't been
+   * initialized yet, so it is error to use. If there is already an element with
+   * the given name defined in an outer scope, then it will become unavailable.
+   */
+  void hide(Element element) {
+    if (element != null) {
+      String name = element.name;
+      if (name != null && !name.isEmpty) {
+        _hiddenElements[name] = element;
+        _hasHiddenName = true;
+      }
+    }
+  }
+
+  @override
+  Element internalLookup(
+      Identifier identifier, String name, LibraryElement referencingLibrary) {
+    Element element = localLookup(name, referencingLibrary);
+    if (element != null) {
+      return element;
+    }
+    // May be there is a hidden Element.
+    if (_hasHiddenName) {
+      Element hiddenElement = _hiddenElements[name];
+      if (hiddenElement != null) {
+        errorListener.onError(new AnalysisError(
+            getSource(identifier),
+            identifier.offset,
+            identifier.length,
+            CompileTimeErrorCode.REFERENCED_BEFORE_DECLARATION, []));
+        return hiddenElement;
+      }
+    }
+    // Check enclosing scope.
+    return enclosingScope.internalLookup(identifier, name, referencingLibrary);
+  }
+}
+
+/**
+ * The scope defined by a function.
+ */
+class FunctionScope extends EnclosedScope {
+  /**
+   * The element representing the function that defines this scope.
+   */
+  final ExecutableElement _functionElement;
+
+  /**
+   * A flag indicating whether the parameters have already been defined, used to
+   * prevent the parameters from being defined multiple times.
+   */
+  bool _parametersDefined = false;
+
+  /**
+   * Initialize a newly created scope, enclosed within the [enclosingScope],
+   * that represents the given [_functionElement].
+   */
+  FunctionScope(Scope enclosingScope, this._functionElement)
+      : super(new EnclosedScope(new EnclosedScope(enclosingScope))) {
+    if (_functionElement == null) {
+      throw new IllegalArgumentException("function element cannot be null");
+    }
+    _defineTypeParameters();
+  }
+
+  /**
+   * Define the parameters for the given function in the scope that encloses
+   * this function.
+   */
+  void defineParameters() {
+    if (_parametersDefined) {
+      return;
+    }
+    _parametersDefined = true;
+    Scope parameterScope = enclosingScope;
+    for (ParameterElement parameter in _functionElement.parameters) {
+      if (!parameter.isInitializingFormal) {
+        parameterScope.define(parameter);
+      }
+    }
+  }
+
+  /**
+   * Define the type parameters for the function.
+   */
+  void _defineTypeParameters() {
+    Scope typeParameterScope = enclosingScope.enclosingScope;
+    for (TypeParameterElement typeParameter
+        in _functionElement.typeParameters) {
+      typeParameterScope.define(typeParameter);
+    }
+  }
+}
+
+/**
+ * The scope defined by a function type alias.
+ */
+class FunctionTypeScope extends EnclosedScope {
+  final FunctionTypeAliasElement _typeElement;
+
+  bool _parametersDefined = false;
+
+  /**
+   * Initialize a newly created scope, enclosed within the [enclosingScope],
+   * that represents the given [_typeElement].
+   */
+  FunctionTypeScope(Scope enclosingScope, this._typeElement)
+      : super(new EnclosedScope(enclosingScope)) {
+    _defineTypeParameters();
+  }
+
+  /**
+   * Define the parameters for the function type alias.
+   */
+  void defineParameters() {
+    if (_parametersDefined) {
+      return;
+    }
+    _parametersDefined = true;
+    for (ParameterElement parameter in _typeElement.parameters) {
+      define(parameter);
+    }
+  }
+
+  /**
+   * Define the type parameters for the function type alias.
+   */
+  void _defineTypeParameters() {
+    Scope typeParameterScope = enclosingScope;
+    for (TypeParameterElement typeParameter in _typeElement.typeParameters) {
+      typeParameterScope.define(typeParameter);
+    }
+  }
+}
+
+/**
+ * The scope statements that can be the target of unlabeled `break` and
+ * `continue` statements.
+ */
+class ImplicitLabelScope {
+  /**
+   * The implicit label scope associated with the top level of a function.
+   */
+  static const ImplicitLabelScope ROOT = const ImplicitLabelScope._(null, null);
+
+  /**
+   * The implicit label scope enclosing this implicit label scope.
+   */
+  final ImplicitLabelScope outerScope;
+
+  /**
+   * The statement that acts as a target for break and/or continue statements
+   * at this scoping level.
+   */
+  final Statement statement;
+
+  /**
+   * Initialize a newly created scope, enclosed within the [outerScope],
+   * representing the given [statement].
+   */
+  const ImplicitLabelScope._(this.outerScope, this.statement);
+
+  /**
+   * Return the statement which should be the target of an unlabeled `break` or
+   * `continue` statement, or `null` if there is no appropriate target.
+   */
+  Statement getTarget(bool isContinue) {
+    if (outerScope == null) {
+      // This scope represents the toplevel of a function body, so it doesn't
+      // match either break or continue.
+      return null;
+    }
+    if (isContinue && statement is SwitchStatement) {
+      return outerScope.getTarget(isContinue);
+    }
+    return statement;
+  }
+
+  /**
+   * Initialize a newly created scope to represent a switch statement or loop
+   * nested within the current scope.  [statement] is the statement associated
+   * with the newly created scope.
+   */
+  ImplicitLabelScope nest(Statement statement) =>
+      new ImplicitLabelScope._(this, statement);
+}
+
+/**
+ * A scope in which a single label is defined.
+ */
+class LabelScope {
+  /**
+   * The label scope enclosing this label scope.
+   */
+  final LabelScope _outerScope;
+
+  /**
+   * The label defined in this scope.
+   */
+  final String _label;
+
+  /**
+   * The element to which the label resolves.
+   */
+  final LabelElement element;
+
+  /**
+   * The AST node to which the label resolves.
+   */
+  final AstNode node;
+
+  /**
+   * Initialize a newly created scope, enclosed within the [_outerScope],
+   * representing the label [_label]. The [node] is the AST node the label
+   * resolves to. The [element] is the element the label resolves to.
+   */
+  LabelScope(this._outerScope, this._label, this.node, this.element);
+
+  /**
+   * Return the LabelScope which defines [targetLabel], or `null` if it is not
+   * defined in this scope.
+   */
+  LabelScope lookup(String targetLabel) {
+    if (_label == targetLabel) {
+      return this;
+    } else if (_outerScope != null) {
+      return _outerScope.lookup(targetLabel);
+    } else {
+      return null;
+    }
+  }
+}
+
+/**
+ * The scope containing all of the names available from imported libraries.
+ */
+class LibraryImportScope extends Scope {
+  /**
+   * The element representing the library in which this scope is enclosed.
+   */
+  final LibraryElement _definingLibrary;
+
+  /**
+   * The listener that is to be informed when an error is encountered.
+   */
+  @override
+  final AnalysisErrorListener errorListener;
+
+  /**
+   * A list of the namespaces representing the names that are available in this scope from imported
+   * libraries.
+   */
+  List<Namespace> _importedNamespaces;
+
+  /**
+   * Initialize a newly created scope representing the names imported into the
+   * [_definingLibrary]. The [errorListener] is the listener that is to be
+   * informed when an error is encountered.
+   */
+  LibraryImportScope(this._definingLibrary, this.errorListener) {
+    _createImportedNamespaces();
+  }
+
+  @override
+  void define(Element element) {
+    if (!Scope.isPrivateName(element.displayName)) {
+      super.define(element);
+    }
+  }
+
+  @override
+  Source getSource(AstNode node) {
+    Source source = super.getSource(node);
+    if (source == null) {
+      source = _definingLibrary.definingCompilationUnit.source;
+    }
+    return source;
+  }
+
+  @override
+  Element internalLookup(
+      Identifier identifier, String name, LibraryElement referencingLibrary) {
+    Element foundElement = localLookup(name, referencingLibrary);
+    if (foundElement != null) {
+      return foundElement;
+    }
+    for (int i = 0; i < _importedNamespaces.length; i++) {
+      Namespace nameSpace = _importedNamespaces[i];
+      Element element = nameSpace.get(name);
+      if (element != null) {
+        if (foundElement == null) {
+          foundElement = element;
+        } else if (!identical(foundElement, element)) {
+          foundElement = MultiplyDefinedElementImpl.fromElements(
+              _definingLibrary.context, foundElement, element);
+        }
+      }
+    }
+    if (foundElement is MultiplyDefinedElementImpl) {
+      foundElement = _removeSdkElements(
+          identifier, name, foundElement as MultiplyDefinedElementImpl);
+    }
+    if (foundElement is MultiplyDefinedElementImpl) {
+      String foundEltName = foundElement.displayName;
+      List<Element> conflictingMembers = foundElement.conflictingElements;
+      int count = conflictingMembers.length;
+      List<String> libraryNames = new List<String>(count);
+      for (int i = 0; i < count; i++) {
+        libraryNames[i] = _getLibraryName(conflictingMembers[i]);
+      }
+      libraryNames.sort();
+      errorListener.onError(new AnalysisError(
+          getSource(identifier),
+          identifier.offset,
+          identifier.length,
+          StaticWarningCode.AMBIGUOUS_IMPORT, [
+        foundEltName,
+        StringUtilities.printListOfQuotedNames(libraryNames)
+      ]));
+      return foundElement;
+    }
+    if (foundElement != null) {
+      defineNameWithoutChecking(name, foundElement);
+    }
+    return foundElement;
+  }
+
+  /**
+   * Create all of the namespaces associated with the libraries imported into
+   * this library. The names are not added to this scope, but are stored for
+   * later reference.
+   */
+  void _createImportedNamespaces() {
+    NamespaceBuilder builder = new NamespaceBuilder();
+    List<ImportElement> imports = _definingLibrary.imports;
+    int count = imports.length;
+    _importedNamespaces = new List<Namespace>(count);
+    for (int i = 0; i < count; i++) {
+      _importedNamespaces[i] =
+          builder.createImportNamespaceForDirective(imports[i]);
+    }
+  }
+
+  /**
+   * Return the name of the library that defines given [element].
+   */
+  String _getLibraryName(Element element) {
+    if (element == null) {
+      return StringUtilities.EMPTY;
+    }
+    LibraryElement library = element.library;
+    if (library == null) {
+      return StringUtilities.EMPTY;
+    }
+    List<ImportElement> imports = _definingLibrary.imports;
+    int count = imports.length;
+    for (int i = 0; i < count; i++) {
+      if (identical(imports[i].importedLibrary, library)) {
+        return library.definingCompilationUnit.displayName;
+      }
+    }
+    List<String> indirectSources = new List<String>();
+    for (int i = 0; i < count; i++) {
+      LibraryElement importedLibrary = imports[i].importedLibrary;
+      if (importedLibrary != null) {
+        for (LibraryElement exportedLibrary
+            in importedLibrary.exportedLibraries) {
+          if (identical(exportedLibrary, library)) {
+            indirectSources
+                .add(importedLibrary.definingCompilationUnit.displayName);
+          }
+        }
+      }
+    }
+    int indirectCount = indirectSources.length;
+    StringBuffer buffer = new StringBuffer();
+    buffer.write(library.definingCompilationUnit.displayName);
+    if (indirectCount > 0) {
+      buffer.write(" (via ");
+      if (indirectCount > 1) {
+        indirectSources.sort();
+        buffer.write(StringUtilities.printListOfQuotedNames(indirectSources));
+      } else {
+        buffer.write(indirectSources[0]);
+      }
+      buffer.write(")");
+    }
+    return buffer.toString();
+  }
+
+  /**
+   * Given a collection of elements (captured by the [foundElement]) that the
+   * [identifier] (with the given [name]) resolved to, remove from the list all
+   * of the names defined in the SDK and return the element(s) that remain.
+   */
+  Element _removeSdkElements(Identifier identifier, String name,
+      MultiplyDefinedElementImpl foundElement) {
+    List<Element> conflictingElements = foundElement.conflictingElements;
+    List<Element> nonSdkElements = new List<Element>();
+    Element sdkElement = null;
+    for (Element member in conflictingElements) {
+      if (member.library.isInSdk) {
+        sdkElement = member;
+      } else {
+        nonSdkElements.add(member);
+      }
+    }
+    if (sdkElement != null && nonSdkElements.length > 0) {
+      String sdkLibName = _getLibraryName(sdkElement);
+      String otherLibName = _getLibraryName(nonSdkElements[0]);
+      errorListener.onError(new AnalysisError(
+          getSource(identifier),
+          identifier.offset,
+          identifier.length,
+          StaticWarningCode.CONFLICTING_DART_IMPORT,
+          [name, sdkLibName, otherLibName]));
+    }
+    if (nonSdkElements.length == conflictingElements.length) {
+      // None of the members were removed
+      return foundElement;
+    } else if (nonSdkElements.length == 1) {
+      // All but one member was removed
+      return nonSdkElements[0];
+    } else if (nonSdkElements.length == 0) {
+      // All members were removed
+      AnalysisEngine.instance.logger
+          .logInformation("Multiply defined SDK element: $foundElement");
+      return foundElement;
+    }
+    return new MultiplyDefinedElementImpl(
+        _definingLibrary.context, nonSdkElements);
+  }
+}
+
+/**
+ * A scope containing all of the names defined in a given library.
+ */
+class LibraryScope extends EnclosedScope {
+  /**
+   * Initialize a newly created scope representing the names defined in the
+   * [definingLibrary]. The [errorListener] is the listener that is to be
+   * informed when an error is encountered
+   */
+  LibraryScope(
+      LibraryElement definingLibrary, AnalysisErrorListener errorListener)
+      : super(new LibraryImportScope(definingLibrary, errorListener)) {
+    _defineTopLevelNames(definingLibrary);
+  }
+
+  @override
+  AnalysisError getErrorForDuplicate(Element existing, Element duplicate) {
+    if (existing is PrefixElement) {
+      // TODO(scheglov) consider providing actual 'nameOffset' from the
+      // synthetic accessor
+      int offset = duplicate.nameOffset;
+      if (duplicate is PropertyAccessorElement) {
+        PropertyAccessorElement accessor = duplicate;
+        if (accessor.isSynthetic) {
+          offset = accessor.variable.nameOffset;
+        }
+      }
+      return new AnalysisError(
+          duplicate.source,
+          offset,
+          duplicate.nameLength,
+          CompileTimeErrorCode.PREFIX_COLLIDES_WITH_TOP_LEVEL_MEMBER,
+          [existing.displayName]);
+    }
+    return super.getErrorForDuplicate(existing, duplicate);
+  }
+
+  /**
+   * Add to this scope all of the public top-level names that are defined in the
+   * given [compilationUnit].
+   */
+  void _defineLocalNames(CompilationUnitElement compilationUnit) {
+    for (PropertyAccessorElement element in compilationUnit.accessors) {
+      define(element);
+    }
+    for (ClassElement element in compilationUnit.enums) {
+      define(element);
+    }
+    for (FunctionElement element in compilationUnit.functions) {
+      define(element);
+    }
+    for (FunctionTypeAliasElement element
+        in compilationUnit.functionTypeAliases) {
+      define(element);
+    }
+    for (ClassElement element in compilationUnit.types) {
+      define(element);
+    }
+  }
+
+  /**
+   * Add to this scope all of the names that are explicitly defined in the
+   * [definingLibrary].
+   */
+  void _defineTopLevelNames(LibraryElement definingLibrary) {
+    for (PrefixElement prefix in definingLibrary.prefixes) {
+      define(prefix);
+    }
+    _defineLocalNames(definingLibrary.definingCompilationUnit);
+    for (CompilationUnitElement compilationUnit in definingLibrary.parts) {
+      _defineLocalNames(compilationUnit);
+    }
+  }
+}
+
+/**
+ * A mapping of identifiers to the elements represented by those identifiers.
+ * Namespaces are the building blocks for scopes.
+ */
+class Namespace {
+  /**
+   * An empty namespace.
+   */
+  static Namespace EMPTY = new Namespace(new HashMap<String, Element>());
+
+  /**
+   * A table mapping names that are defined in this namespace to the element
+   * representing the thing declared with that name.
+   */
+  final HashMap<String, Element> _definedNames;
+
+  /**
+   * Initialize a newly created namespace to have the [_definedNames].
+   */
+  Namespace(this._definedNames);
+
+  /**
+   * Return a table containing the same mappings as those defined by this
+   * namespace.
+   */
+  Map<String, Element> get definedNames => _definedNames;
+
+  /**
+   * Return the element in this namespace that is available to the containing
+   * scope using the given name.
+   */
+  Element get(String name) => _definedNames[name];
+}
+
+/**
+ * The builder used to build a namespace. Namespace builders are thread-safe and
+ * re-usable.
+ */
+class NamespaceBuilder {
+  /**
+   * Create a namespace representing the export namespace of the given [element].
+   */
+  Namespace createExportNamespaceForDirective(ExportElement element) {
+    LibraryElement exportedLibrary = element.exportedLibrary;
+    if (exportedLibrary == null) {
+      //
+      // The exported library will be null if the URI does not reference a valid
+      // library.
+      //
+      return Namespace.EMPTY;
+    }
+    HashMap<String, Element> exportedNames = _getExportMapping(exportedLibrary);
+    exportedNames = _applyCombinators(exportedNames, element.combinators);
+    return new Namespace(exportedNames);
+  }
+
+  /**
+   * Create a namespace representing the export namespace of the given [library].
+   */
+  Namespace createExportNamespaceForLibrary(LibraryElement library) {
+    HashMap<String, Element> exportedNames = _getExportMapping(library);
+    return new Namespace(exportedNames);
+  }
+
+  /**
+   * Create a namespace representing the import namespace of the given [element].
+   */
+  Namespace createImportNamespaceForDirective(ImportElement element) {
+    LibraryElement importedLibrary = element.importedLibrary;
+    if (importedLibrary == null) {
+      //
+      // The imported library will be null if the URI does not reference a valid
+      // library.
+      //
+      return Namespace.EMPTY;
+    }
+    HashMap<String, Element> exportedNames = _getExportMapping(importedLibrary);
+    exportedNames = _applyCombinators(exportedNames, element.combinators);
+    exportedNames = _applyPrefix(exportedNames, element.prefix);
+    return new Namespace(exportedNames);
+  }
+
+  /**
+   * Create a namespace representing the public namespace of the given
+   * [library].
+   */
+  Namespace createPublicNamespaceForLibrary(LibraryElement library) {
+    HashMap<String, Element> definedNames = new HashMap<String, Element>();
+    _addPublicNames(definedNames, library.definingCompilationUnit);
+    for (CompilationUnitElement compilationUnit in library.parts) {
+      _addPublicNames(definedNames, compilationUnit);
+    }
+    return new Namespace(definedNames);
+  }
+
+  /**
+   * Add all of the names in the given [namespace] to the table of
+   * [definedNames].
+   */
+  void _addAllFromNamespace(
+      Map<String, Element> definedNames, Namespace namespace) {
+    if (namespace != null) {
+      definedNames.addAll(namespace.definedNames);
+    }
+  }
+
+  /**
+   * Add the given [element] to the table of [definedNames] if it has a
+   * publicly visible name.
+   */
+  void _addIfPublic(Map<String, Element> definedNames, Element element) {
+    String name = element.name;
+    if (name != null && !Scope.isPrivateName(name)) {
+      definedNames[name] = element;
+    }
+  }
+
+  /**
+   * Add to the table of [definedNames] all of the public top-level names that
+   * are defined in the given [compilationUnit].
+   *          namespace
+   */
+  void _addPublicNames(Map<String, Element> definedNames,
+      CompilationUnitElement compilationUnit) {
+    for (PropertyAccessorElement element in compilationUnit.accessors) {
+      _addIfPublic(definedNames, element);
+    }
+    for (ClassElement element in compilationUnit.enums) {
+      _addIfPublic(definedNames, element);
+    }
+    for (FunctionElement element in compilationUnit.functions) {
+      _addIfPublic(definedNames, element);
+    }
+    for (FunctionTypeAliasElement element
+        in compilationUnit.functionTypeAliases) {
+      _addIfPublic(definedNames, element);
+    }
+    for (ClassElement element in compilationUnit.types) {
+      _addIfPublic(definedNames, element);
+    }
+  }
+
+  /**
+   * Apply the given [combinators] to all of the names in the given table of
+   * [definedNames].
+   */
+  HashMap<String, Element> _applyCombinators(
+      HashMap<String, Element> definedNames,
+      List<NamespaceCombinator> combinators) {
+    for (NamespaceCombinator combinator in combinators) {
+      if (combinator is HideElementCombinator) {
+        definedNames = _hide(definedNames, combinator.hiddenNames);
+      } else if (combinator is ShowElementCombinator) {
+        definedNames = _show(definedNames, combinator.shownNames);
+      } else {
+        // Internal error.
+        AnalysisEngine.instance.logger
+            .logError("Unknown type of combinator: ${combinator.runtimeType}");
+      }
+    }
+    return definedNames;
+  }
+
+  /**
+   * Apply the prefix defined by the [prefixElement] to all of the names in the
+   * table of [definedNames].
+   */
+  HashMap<String, Element> _applyPrefix(
+      HashMap<String, Element> definedNames, PrefixElement prefixElement) {
+    if (prefixElement != null) {
+      String prefix = prefixElement.name;
+      HashMap<String, Element> newNames = new HashMap<String, Element>();
+      definedNames.forEach((String name, Element element) {
+        newNames["$prefix.$name"] = element;
+      });
+      return newNames;
+    } else {
+      return definedNames;
+    }
+  }
+
+  /**
+   * Create a mapping table representing the export namespace of the given
+   * [library]. The set of [visitedElements] contains the libraries that do not
+   * need to be visited when processing the export directives of the given
+   * library because all of the names defined by them will be added by another
+   * library.
+   */
+  HashMap<String, Element> _computeExportMapping(
+      LibraryElement library, HashSet<LibraryElement> visitedElements) {
+    visitedElements.add(library);
+    try {
+      HashMap<String, Element> definedNames = new HashMap<String, Element>();
+      for (ExportElement element in library.exports) {
+        LibraryElement exportedLibrary = element.exportedLibrary;
+        if (exportedLibrary != null &&
+            !visitedElements.contains(exportedLibrary)) {
+          //
+          // The exported library will be null if the URI does not reference a
+          // valid library.
+          //
+          HashMap<String, Element> exportedNames =
+              _computeExportMapping(exportedLibrary, visitedElements);
+          exportedNames = _applyCombinators(exportedNames, element.combinators);
+          definedNames.addAll(exportedNames);
+        }
+      }
+      _addAllFromNamespace(
+          definedNames,
+          (library.context as InternalAnalysisContext)
+              .getPublicNamespace(library));
+      return definedNames;
+    } finally {
+      visitedElements.remove(library);
+    }
+  }
+
+  HashMap<String, Element> _getExportMapping(LibraryElement library) {
+    if (library is LibraryElementImpl) {
+      if (library.exportNamespace != null) {
+        return library.exportNamespace.definedNames;
+      } else {
+        HashMap<String, Element> exportMapping =
+            _computeExportMapping(library, new HashSet<LibraryElement>());
+        library.exportNamespace = new Namespace(exportMapping);
+        return exportMapping;
+      }
+    }
+    return _computeExportMapping(library, new HashSet<LibraryElement>());
+  }
+
+  /**
+   * Return a new map of names which has all the names from [definedNames]
+   * with exception of [hiddenNames].
+   */
+  Map<String, Element> _hide(
+      HashMap<String, Element> definedNames, List<String> hiddenNames) {
+    HashMap<String, Element> newNames =
+        new HashMap<String, Element>.from(definedNames);
+    for (String name in hiddenNames) {
+      newNames.remove(name);
+      newNames.remove("$name=");
+    }
+    return newNames;
+  }
+
+  /**
+   * Return a new map of names which has only [shownNames] from [definedNames].
+   */
+  HashMap<String, Element> _show(
+      HashMap<String, Element> definedNames, List<String> shownNames) {
+    HashMap<String, Element> newNames = new HashMap<String, Element>();
+    for (String name in shownNames) {
+      Element element = definedNames[name];
+      if (element != null) {
+        newNames[name] = element;
+      }
+      String setterName = "$name=";
+      element = definedNames[setterName];
+      if (element != null) {
+        newNames[setterName] = element;
+      }
+    }
+    return newNames;
+  }
+}
+
+/**
+ * A name scope used by the resolver to determine which names are visible at any
+ * given point in the code.
+ */
+abstract class Scope {
+  /**
+   * The prefix used to mark an identifier as being private to its library.
+   */
+  static int PRIVATE_NAME_PREFIX = 0x5F;
+
+  /**
+   * The suffix added to the declared name of a setter when looking up the
+   * setter. Used to disambiguate between a getter and a setter that have the
+   * same name.
+   */
+  static String SETTER_SUFFIX = "=";
+
+  /**
+   * The name used to look up the method used to implement the unary minus
+   * operator. Used to disambiguate between the unary and binary operators.
+   */
+  static String UNARY_MINUS = "unary-";
+
+  /**
+   * A table mapping names that are defined in this scope to the element
+   * representing the thing declared with that name.
+   */
+  HashMap<String, Element> _definedNames = new HashMap<String, Element>();
+
+  /**
+   * A flag indicating whether there are any names defined in this scope.
+   */
+  bool _hasName = false;
+
+  /**
+   * Return the scope in which this scope is lexically enclosed.
+   */
+  Scope get enclosingScope => null;
+
+  /**
+   * Return the listener that is to be informed when an error is encountered.
+   */
+  AnalysisErrorListener get errorListener;
+
+  /**
+   * Add the given [element] to this scope. If there is already an element with
+   * the given name defined in this scope, then an error will be generated and
+   * the original element will continue to be mapped to the name. If there is an
+   * element with the given name in an enclosing scope, then a warning will be
+   * generated but the given element will hide the inherited element.
+   */
+  void define(Element element) {
+    String name = _getName(element);
+    if (name != null && !name.isEmpty) {
+      if (_definedNames.containsKey(name)) {
+        errorListener
+            .onError(getErrorForDuplicate(_definedNames[name], element));
+      } else {
+        _definedNames[name] = element;
+        _hasName = true;
+      }
+    }
+  }
+
+  /**
+   * Add the given [element] to this scope without checking for duplication or
+   * hiding.
+   */
+  void defineNameWithoutChecking(String name, Element element) {
+    _definedNames[name] = element;
+    _hasName = true;
+  }
+
+  /**
+   * Add the given [element] to this scope without checking for duplication or
+   * hiding.
+   */
+  void defineWithoutChecking(Element element) {
+    _definedNames[_getName(element)] = element;
+    _hasName = true;
+  }
+
+  /**
+   * Return the error code to be used when reporting that a name being defined
+   * locally conflicts with another element of the same name in the local scope.
+   * [existing] is the first element to be declared with the conflicting name,
+   * while [duplicate] another element declared with the conflicting name.
+   */
+  AnalysisError getErrorForDuplicate(Element existing, Element duplicate) {
+    // TODO(brianwilkerson) Customize the error message based on the types of
+    // elements that share the same name.
+    // TODO(jwren) There are 4 error codes for duplicate, but only 1 is being
+    // generated.
+    Source source = duplicate.source;
+    return new AnalysisError(source, duplicate.nameOffset, duplicate.nameLength,
+        CompileTimeErrorCode.DUPLICATE_DEFINITION, [existing.displayName]);
+  }
+
+  /**
+   * Return the source that contains the given [identifier], or the source
+   * associated with this scope if the source containing the identifier could
+   * not be determined.
+   */
+  Source getSource(AstNode identifier) {
+    CompilationUnit unit =
+        identifier.getAncestor((node) => node is CompilationUnit);
+    if (unit != null) {
+      CompilationUnitElement unitElement = unit.element;
+      if (unitElement != null) {
+        return unitElement.source;
+      }
+    }
+    return null;
+  }
+
+  /**
+   * Return the element with which the given [name] is associated, or `null` if
+   * the name is not defined within this scope. The [identifier] is the
+   * identifier node to lookup element for, used to report correct kind of a
+   * problem and associate problem with. The [referencingLibrary] is the library
+   * that contains the reference to the name, used to implement library-level
+   * privacy.
+   */
+  Element internalLookup(
+      Identifier identifier, String name, LibraryElement referencingLibrary);
+
+  /**
+   * Return the element with which the given [name] is associated, or `null` if
+   * the name is not defined within this scope. This method only returns
+   * elements that are directly defined within this scope, not elements that are
+   * defined in an enclosing scope. The [referencingLibrary] is the library that
+   * contains the reference to the name, used to implement library-level privacy.
+   */
+  Element localLookup(String name, LibraryElement referencingLibrary) {
+    if (_hasName) {
+      return _definedNames[name];
+    }
+    return null;
+  }
+
+  /**
+   * Return the element with which the given [identifier] is associated, or
+   * `null` if the name is not defined within this scope. The
+   * [referencingLibrary] is the library that contains the reference to the
+   * name, used to implement library-level privacy.
+   */
+  Element lookup(Identifier identifier, LibraryElement referencingLibrary) =>
+      internalLookup(identifier, identifier.name, referencingLibrary);
+
+  /**
+   * Return the name that will be used to look up the given [element].
+   */
+  String _getName(Element element) {
+    if (element is MethodElement) {
+      MethodElement method = element;
+      if (method.name == "-" && method.parameters.length == 0) {
+        return UNARY_MINUS;
+      }
+    }
+    return element.name;
+  }
+
+  /**
+   * Return `true` if the given [name] is a library-private name.
+   */
+  static bool isPrivateName(String name) =>
+      name != null && StringUtilities.startsWithChar(name, PRIVATE_NAME_PREFIX);
+}
+
+/**
+ * The scope defined by the type parameters in a class.
+ */
+class TypeParameterScope extends EnclosedScope {
+  /**
+   * Initialize a newly created scope, enclosed within the [enclosingScope],
+   * that defined the type parameters from the given [classElement].
+   */
+  TypeParameterScope(Scope enclosingScope, ClassElement classElement)
+      : super(enclosingScope) {
+    if (classElement == null) {
+      throw new IllegalArgumentException("class element cannot be null");
+    }
+    _defineTypeParameters(classElement);
+  }
+
+  /**
+   * Define the type parameters declared by the [classElement].
+   */
+  void _defineTypeParameters(ClassElement classElement) {
+    for (TypeParameterElement typeParameter in classElement.typeParameters) {
+      define(typeParameter);
+    }
+  }
+}