Introduce code to resynthesize element models from summaries.

pkg/analyzer/lib/src/summary/resynthesize.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.
+
+library summary_resynthesizer;
+
+import 'package:analyzer/analyzer.dart';
+import 'package:analyzer/src/generated/element.dart';
+import 'package:analyzer/src/generated/element_handle.dart';
+import 'package:analyzer/src/generated/engine.dart';
+import 'package:analyzer/src/generated/resolver.dart';
+import 'package:analyzer/src/generated/source_io.dart';
+import 'package:analyzer/src/summary/format.dart';
+
+/**
+ * Callback used by [SummaryResynthesizer] to obtain the summary for a given
+ * URI.
+ */
+typedef PrelinkedLibrary GetSummaryCallback(String uri);
+
+/**
+ * Specialization of [FunctionTypeImpl] used for function types resynthesized
+ * from summaries.
+ */
+class ResynthesizedFunctionTypeImpl extends FunctionTypeImpl
+    with ResynthesizedType {
+  final SummaryResynthesizer summaryResynthesizer;
+
+  ResynthesizedFunctionTypeImpl(
+      FunctionTypeAliasElement element, String name, this.summaryResynthesizer)
+      : super.elementWithName(element, name);
+
+  int get _numTypeParameters {
+    FunctionTypeAliasElement element = this.element;
+    return element.typeParameters.length;
+  }
+}
+
+/**
+ * Specialization of [InterfaceTypeImpl] used for interface types resynthesized
+ * from summaries.
+ */
+class ResynthesizedInterfaceTypeImpl extends InterfaceTypeImpl
+    with ResynthesizedType {
+  final SummaryResynthesizer summaryResynthesizer;
+
+  ResynthesizedInterfaceTypeImpl(
+      ClassElement element, String name, this.summaryResynthesizer)
+      : super.elementWithName(element, name);
+
+  int get _numTypeParameters => element.typeParameters.length;
+}
+
+/**
+ * Common code for types resynthesized from summaries.  This code takes care of
+ * filling in the appropriate number of copies of `dynamic` when it is queried
+ * for type parameters on a bare type reference (i.e. it converts `List` to
+ * `List<dynamic>`).
+ */
+abstract class ResynthesizedType implements DartType {
+  /**
+   * The type arguments, if known.  Otherwise `null`.
+   */
+  List<DartType> _typeArguments;
+
+  SummaryResynthesizer get summaryResynthesizer;
+
+  List<DartType> get typeArguments {
+    if (_typeArguments == null) {
+      // Default to replicating "dynamic" as many times as the class element
+      // requires.
+      _typeArguments = new List<DartType>.filled(
+          _numTypeParameters, summaryResynthesizer.typeProvider.dynamicType);
+    }
+    return _typeArguments;
+  }
+
+  int get _numTypeParameters;
+}
+
+/**
+ * Implementation of [ElementResynthesizer] used when resynthesizing an element
+ * model from summaries.
+ */
+class SummaryResynthesizer extends ElementResynthesizer {
+  /**
+   * Callback used to obtain the summary for a given URI.
+   */
+  final GetSummaryCallback getSummary;
+
+  /**
+   * Source factory used to convert URIs to [Source] objects.
+   */
+  final SourceFactory sourceFactory;
+
+  /**
+   * Cache of [Source] objects that have already been converted from URIs.
+   */
+  final Map<String, Source> _sources = <String, Source>{};
+
+  /**
+   * The [TypeProvider] used to obtain core types (such as Object, int, List,
+   * and dynamic) during resynthesis.
+   *
+   * TODO(paulberry): will this create a chicken-and-egg problem when trying to
+   * resynthesize the core library from summaries?
+   */
+  final TypeProvider typeProvider;
+
+  /**
+   * Map of top level elements resynthesized from summaries.  The three map
+   * keys are the first three elements of the element's location (the library
+   * URI, the compilation unit URI, and the name of the top level declaration).
+   */
+  final Map<String, Map<String, Map<String, Element>>> _resynthesizedElements =
+      <String, Map<String, Map<String, Element>>>{};
+
+  /**
+   * Map of libraries which have been resynthesized from summaries.  The map
+   * key is the library URI.
+   */
+  final Map<String, LibraryElement> _resynthesizedLibraries =
+      <String, LibraryElement>{};
+
+  SummaryResynthesizer(
+      AnalysisContext context, this.getSummary, this.sourceFactory)
+      : super(context),
+        typeProvider = context.typeProvider;
+
+  /**
+   * Number of libraries that have been resynthesized so far.
+   */
+  int get resynthesisCount => _resynthesizedLibraries.length;
+
+  @override
+  Element getElement(ElementLocation location) {
+    if (location.components.length == 1) {
+      return getLibraryElement(location.components[0]);
+    } else if (location.components.length == 3) {
+      String uri = location.components[0];
+      Map<String, Map<String, Element>> libraryMap =
+          _resynthesizedElements[uri];
+      if (libraryMap == null) {
+        getLibraryElement(uri);
+        libraryMap = _resynthesizedElements[uri];
+        assert(libraryMap != null);
+      }
+      Element element = libraryMap[location.components[1]]

[scheglov, 2015/12/16 01:46:49]

Can this expression be null?

[Paul Berry, 2015/12/16 16:34:20]

Good point.  It could happen, if files are updated and we forget to re-link
them, or there is a bug in the re-linking logic (which has not yet been
written).  Either of those circumstances could lead to one summary's "prelinked"
information referring to a compilation unit which does not exist.

I've added additional error checking logic to catch this scenario, and I've also
updated the exception below to say "Element not found in summary: $location" so
that if this situation ever does arise, it will be easier to figure out what
happened.

+          [location.components[2]];
+      if (element == null) {
+        throw new Exception('Failed to resynthesize $location');
+      }
+      assert(element != null);
+      return element;
+    } else {
+      throw new UnimplementedError(location.toString());
+    }
+  }
+
+  /**
+   * Get the [LibraryElement] for the given [uri], resynthesizing it if it
+   * hasn't been resynthesized already.
+   */
+  LibraryElement getLibraryElement(String uri) {
+    return _resynthesizedLibraries.putIfAbsent(uri, () {
+      PrelinkedLibrary serializedLibrary = getSummary(uri);
+      _LibraryResynthesizer libraryResynthesizer =
+          new _LibraryResynthesizer(this, serializedLibrary, _getSource(uri));
+      LibraryElement library = libraryResynthesizer.buildLibrary();
+      _resynthesizedElements[uri] = libraryResynthesizer.resummarizedElements;
+      return library;
+    });
+  }
+
+  /**
+   * Get the [Source] object for the given [uri].
+   */
+  Source _getSource(String uri) {
+    return _sources.putIfAbsent(uri, () => sourceFactory.forUri(uri));
+  }
+}
+
+/**
+ * An instance of [_LibraryResynthesizer] is responsible for resynthesizing the
+ * elements in a single library from that library's summary.
+ */
+class _LibraryResynthesizer {
+  /**
+   * The [SummaryResynthesizer] which is being used to obtain summaries.
+   */
+  final SummaryResynthesizer summaryResynthesizer;
+
+  /**
+   * The library to be resynthesized.
+   */
+  final PrelinkedLibrary prelinkedLibrary;
+
+  /**
+   * [Source] object for the library to be resynthesized.
+   */
+  final Source librarySource;
+
+  /**
+   * [ElementHolder] into which resynthesized elements should be placed.  This
+   * object is recreated afresh for each unit in the library, and is used to
+   * populate the [CompilationUnitElement].
+   */
+  ElementHolder unitHolder;
+
+  /**
+   * The [PrelinkedUnit] from which elements are currently being resynthesized.
+   */
+  PrelinkedUnit prelinkedUnit;
+
+  /**
+   * Map of top level elements that have been resynthesized so far.  The first
+   * key is the URI of the compilation unit; the second is the name of the top
+   * level element.
+   */
+  final Map<String, Map<String, Element>> resummarizedElements =
+      <String, Map<String, Element>>{};
+
+  /**
+   * Type parameters for the class or typedef currently being resynthesized.
+   *
+   * TODO(paulberry): extend this to do the right thing for generic methods.
+   */
+  List<TypeParameterElement> currentTypeParameters;
+
+  _LibraryResynthesizer(this.summaryResynthesizer,
+      PrelinkedLibrary serializedLibrary, this.librarySource)
+      : prelinkedLibrary = serializedLibrary;
+
+  /**
+   * Resynthesize a [ClassElement] and place it in [unitHolder].
+   */
+  void buildClass(UnlinkedClass serializedClass) {
+    try {
+      currentTypeParameters =
+          serializedClass.typeParameters.map(buildTypeParameter).toList();
+      for (int i = 0; i < serializedClass.typeParameters.length; i++) {
+        finishTypeParameter(
+            serializedClass.typeParameters[i], currentTypeParameters[i]);
+      }
+      ClassElementImpl classElement;
+      if (serializedClass.isMixinApplication) {
+        classElement = new ClassElementImpl(serializedClass.name, -1);
+        classElement.setModifier(Modifier.MIXIN_APPLICATION, true);
+      } else {
+        classElement = new ClassElementImpl(serializedClass.name, -1);

[Brian Wilkerson, 2015/12/16 00:29:07]

Unless I'm missing something, this line is inside both the 'then' and 'else'
clauses.

[Paul Berry, 2015/12/16 16:34:20]

Oops, you're right.  Fixed.

+      }
+      InterfaceTypeImpl correspondingType = new InterfaceTypeImpl(classElement);
+      if (serializedClass.supertype != null) {
+        classElement.supertype = buildType(serializedClass.supertype);
+      } else {
+        // TODO(paulberry): don't make Object point to itself.
+        classElement.supertype = summaryResynthesizer.typeProvider.objectType;
+      }
+      classElement.interfaces =
+          serializedClass.interfaces.map(buildType).toList();
+      classElement.mixins = serializedClass.mixins.map(buildType).toList();
+      classElement.typeParameters = currentTypeParameters;
+      ElementHolder memberHolder = new ElementHolder();
+      bool constructorFound = false;
+      for (UnlinkedExecutable serializedExecutable
+          in serializedClass.executables) {
+        switch (serializedExecutable.kind) {
+          case UnlinkedExecutableKind.constructor:
+            constructorFound = true;
+            buildConstructor(serializedExecutable, memberHolder);
+            break;
+          case UnlinkedExecutableKind.functionOrMethod:
+          case UnlinkedExecutableKind.getter:
+          case UnlinkedExecutableKind.setter:
+            buildExecutable(serializedExecutable, memberHolder);
+            break;
+        }
+      }
+      for (UnlinkedVariable serializedVariable in serializedClass.fields) {
+        buildVariable(serializedVariable, memberHolder);
+      }
+      if (!serializedClass.isMixinApplication) {
+        if (!constructorFound) {
+          // Synthesize implicit constructors.
+          ConstructorElementImpl constructor =
+              new ConstructorElementImpl('', -1);
+          constructor.setModifier(Modifier.SYNTHETIC, true);
+          constructor.returnType = correspondingType;
+          constructor.type = new FunctionTypeImpl(constructor);
+          memberHolder.addConstructor(constructor);
+        }
+        classElement.constructors = memberHolder.constructors;
+      }
+      classElement.accessors = memberHolder.accessors;
+      classElement.fields = memberHolder.fields;
+      classElement.methods = memberHolder.methods;
+      correspondingType.typeArguments =
+          currentTypeParameters.map((param) => param.type).toList();
+      classElement.type = correspondingType;
+      unitHolder.addType(classElement);
+    } finally {
+      currentTypeParameters = null;
+    }
+  }
+
+  /**
+   * Resynthesize a [NamespaceCombinator].
+   */
+  NamespaceCombinator buildCombinator(UnlinkedCombinator serializedCombinator) {
+    if (serializedCombinator.shows.isNotEmpty) {
+      ShowElementCombinatorImpl combinator = new ShowElementCombinatorImpl();
+      combinator.shownNames = serializedCombinator.shows
+          .map((UnlinkedCombinatorName n) => n.name)
+          .toList();
+      return combinator;
+    } else {
+      HideElementCombinatorImpl combinator = new HideElementCombinatorImpl();
+      combinator.hiddenNames = serializedCombinator.hides
+          .map((UnlinkedCombinatorName n) => n.name)
+          .toList();
+      return combinator;
+    }
+  }
+
+  /**
+   * Resynthesize a [ConstructorElement] and place it in the given [holder].
+   */
+  void buildConstructor(
+      UnlinkedExecutable serializedExecutable, ElementHolder holder) {
+    assert(serializedExecutable.kind == UnlinkedExecutableKind.constructor);
+    ConstructorElementImpl constructorElement =
+        new ConstructorElementImpl(serializedExecutable.name, -1);
+    buildExecutableCommonParts(constructorElement, serializedExecutable);
+    if (serializedExecutable.isFactory) {
+      constructorElement.setModifier(Modifier.FACTORY, true);

[scheglov, 2015/12/16 01:46:49]

ConstructorElementImpl has a setter "factory".
...and the setter "const2".
Ouch.

[Paul Berry, 2015/12/16 16:34:20]

Good point.  I'll do a follow-up commit that replaces these calls to
`setModifier` with calls to the appropriate setters where possible.

+    }
+    if (serializedExecutable.isConst) {
+      constructorElement.setModifier(Modifier.CONST, true);
+    }
+    holder.addConstructor(constructorElement);
+  }
+
+  /**
+   * Resynthesize the [ClassElement] corresponding to an enum, along with the
+   * associated fields and implicit accessors.
+   */
+  void buildEnum(UnlinkedEnum serializedEnum) {
+    ClassElementImpl classElement =
+        new ClassElementImpl(serializedEnum.name, -1);

[Brian Wilkerson, 2015/12/16 00:29:07]

I assume that we'll get offsets at some point.

[Paul Berry, 2015/12/16 16:34:20]

Yes, that's the plan.  I've added a TODO comment to capture this.

+    classElement.setModifier(Modifier.ENUM, true);
+    InterfaceType enumType = new InterfaceTypeImpl(classElement);
+    classElement.type = enumType;
+    classElement.supertype = summaryResynthesizer.typeProvider.objectType;
+    ElementHolder memberHolder = new ElementHolder();
+    FieldElementImpl indexField = new FieldElementImpl('index', -1);
+    indexField.setModifier(Modifier.FINAL, true);
+    indexField.setModifier(Modifier.SYNTHETIC, true);
+    indexField.type = summaryResynthesizer.typeProvider.intType;
+    memberHolder.addField(indexField);
+    buildImplicitAccessors(indexField, memberHolder);
+    FieldElementImpl valuesField = new ConstFieldElementImpl('values', -1);
+    valuesField.setModifier(Modifier.SYNTHETIC, true);
+    valuesField.setModifier(Modifier.CONST, true);
+    valuesField.setModifier(Modifier.STATIC, true);
+    valuesField.type = summaryResynthesizer.typeProvider.listType
+        .substitute4(<DartType>[enumType]);
+    memberHolder.addField(valuesField);
+    buildImplicitAccessors(valuesField, memberHolder);
+    for (UnlinkedEnumValue serializedEnumValue in serializedEnum.values) {
+      ConstFieldElementImpl valueField =
+          new ConstFieldElementImpl(serializedEnumValue.name, -1);
+      valueField.setModifier(Modifier.CONST, true);
+      valueField.setModifier(Modifier.STATIC, true);
+      valueField.type = enumType;
+      memberHolder.addField(valueField);
+      buildImplicitAccessors(valueField, memberHolder);
+    }
+    classElement.fields = memberHolder.fields;
+    classElement.accessors = memberHolder.accessors;
+    classElement.constructors = <ConstructorElement>[];
+    unitHolder.addEnum(classElement);
+  }
+
+  /**
+   * Resynthesize an [ExecutableElement] and place it in the given [holder].
+   */
+  void buildExecutable(UnlinkedExecutable serializedExecutable,
+      [ElementHolder holder]) {
+    bool isTopLevel = holder == null;
+    if (holder == null) {
+      holder = unitHolder;
+    }
+    String name = serializedExecutable.name;
+    if (name.endsWith('=')) {
+      name = name.substring(0, name.length - 1);
+    }
+    UnlinkedExecutableKind kind = serializedExecutable.kind;
+    switch (kind) {
+      case UnlinkedExecutableKind.functionOrMethod:
+        if (isTopLevel) {
+          FunctionElementImpl executableElement =
+              new FunctionElementImpl(name, -1);
+          buildExecutableCommonParts(executableElement, serializedExecutable);
+          holder.addFunction(executableElement);
+        } else {
+          MethodElementImpl executableElement = new MethodElementImpl(name, -1);
+          buildExecutableCommonParts(executableElement, serializedExecutable);
+          executableElement.setModifier(
+              Modifier.STATIC, serializedExecutable.isStatic);
+          holder.addMethod(executableElement);
+        }
+        break;
+      case UnlinkedExecutableKind.getter:
+      case UnlinkedExecutableKind.setter:
+        PropertyAccessorElementImpl executableElement =
+            new PropertyAccessorElementImpl(name, -1);
+        if (isTopLevel) {
+          executableElement.setModifier(Modifier.STATIC, true);
+        } else {
+          executableElement.setModifier(
+              Modifier.STATIC, serializedExecutable.isStatic);
+        }
+        buildExecutableCommonParts(executableElement, serializedExecutable);
+        DartType type;
+        if (kind == UnlinkedExecutableKind.getter) {
+          executableElement.setModifier(Modifier.GETTER, true);
+          type = executableElement.returnType;
+        } else {
+          executableElement.setModifier(Modifier.SETTER, true);
+          type = executableElement.parameters[0].type;
+        }
+        holder.addAccessor(executableElement);
+        // TODO(paulberry): consider removing implicit variables from the
+        // element model; the spec doesn't call for them, and they cause
+        // trouble when getters/setters exist in different parts.
+        PropertyInducingElementImpl implicitVariable;
+        if (isTopLevel) {
+          implicitVariable = buildImplicitTopLevelVariable(name, kind, holder);
+        } else {
+          implicitVariable = buildImplicitField(name, type, kind, holder);
+          implicitVariable.setModifier(
+              Modifier.STATIC, serializedExecutable.isStatic);
+        }
+        executableElement.variable = implicitVariable;
+        if (kind == UnlinkedExecutableKind.getter) {
+          implicitVariable.getter = executableElement;
+        } else {
+          implicitVariable.setter = executableElement;
+        }
+        // TODO(paulberry): do the right thing when getter and setter are in
+        // different units.
+        break;
+      default:
+        // The only other executable type is a constructor, and that is handled
+        // separately (in [buildConstructor].  So this code should be
+        // unreachable.
+        assert(false);
+    }
+  }
+
+  /**
+   * Handle the parts of an executable element that are common to constructors,
+   * functions, methods, getters, and setters.
+   */
+  void buildExecutableCommonParts(ExecutableElementImpl executableElement,
+      UnlinkedExecutable serializedExecutable) {
+    executableElement.parameters =
+        serializedExecutable.parameters.map(buildParameter).toList();
+    if (serializedExecutable.returnType != null) {
+      executableElement.returnType = buildType(serializedExecutable.returnType);
+    } else {
+      executableElement.returnType = VoidTypeImpl.instance;
+    }
+    executableElement.type = new FunctionTypeImpl(executableElement);
+    if (serializedExecutable.hasImplicitReturnType) {
+      executableElement.setModifier(Modifier.IMPLICIT_TYPE, true);
+    }
+  }
+
+  /**
+   * Resynthesize an [ExportElement],
+   */
+  ExportElement buildExport(UnlinkedExport serializedExport) {
+    ExportElementImpl exportElement = new ExportElementImpl(0);
+    String exportedLibraryUri = summaryResynthesizer.sourceFactory
+        .resolveUri(librarySource, serializedExport.uri)
+        .uri
+        .toString();
+    exportElement.exportedLibrary = new LibraryElementHandle(
+        summaryResynthesizer,
+        new ElementLocationImpl.con3(<String>[exportedLibraryUri]));
+    exportElement.uri = serializedExport.uri;
+    exportElement.combinators =
+        serializedExport.combinators.map(buildCombinator).toList();
+    return exportElement;
+  }
+
+  /**
+   * Resynthesize a [FieldElement].
+   */
+  FieldElement buildField(UnlinkedVariable serializedField) {
+    FieldElementImpl fieldElement =
+        new FieldElementImpl(serializedField.name, -1);
+    fieldElement.type = buildType(serializedField.type);
+    if (serializedField.isConst) {
+      fieldElement.setModifier(Modifier.CONST, true);
+    }
+    return fieldElement;
+  }
+
+  /**
+   * Build the implicit getter and setter associated with [element], and place
+   * them in [holder].
+   */
+  void buildImplicitAccessors(
+      PropertyInducingElementImpl element, ElementHolder holder) {
+    String name = element.name;
+    DartType type = element.type;
+    PropertyAccessorElementImpl getter =
+        new PropertyAccessorElementImpl(name, -1);
+    getter.setModifier(Modifier.GETTER, true);
+    getter.setModifier(Modifier.STATIC, element.isStatic);
+    getter.setModifier(Modifier.SYNTHETIC, true);
+    getter.returnType = type;
+    getter.type = new FunctionTypeImpl(getter);
+    getter.variable = element;
+    holder.addAccessor(getter);
+    element.getter = getter;
+    if (!(element.isConst || element.isFinal)) {
+      PropertyAccessorElementImpl setter =
+          new PropertyAccessorElementImpl(name, -1);
+      setter.setModifier(Modifier.SETTER, true);
+      setter.setModifier(Modifier.STATIC, element.isStatic);
+      setter.setModifier(Modifier.SYNTHETIC, true);
+      setter.parameters = <ParameterElement>[
+        new ParameterElementImpl('_$name', -1)
+          ..setModifier(Modifier.SYNTHETIC, true)
+          ..type = type
+          ..parameterKind = ParameterKind.REQUIRED
+      ];
+      setter.returnType = VoidTypeImpl.instance;
+      setter.type = new FunctionTypeImpl(setter);
+      setter.variable = element;
+      holder.addAccessor(setter);
+      element.setter = setter;
+    }
+  }
+
+  /**
+   * Build the implicit field associated with a getter or setter, and place it
+   * in [holder].
+   */
+  PropertyInducingElementImpl buildImplicitField(String name, DartType type,
+      UnlinkedExecutableKind kind, ElementHolder holder) {
+    if (holder.getField(name) == null) {
+      FieldElementImpl field = new FieldElementImpl(name, -1);
+      field.setModifier(Modifier.SYNTHETIC, true);
+      if (kind == UnlinkedExecutableKind.getter) {
+        field.setModifier(Modifier.FINAL, true);
+      }
+      field.type = type;
+      holder.addField(field);
+      return field;
+    } else {
+      // TODO(paulberry): if adding a setter where there was previously
+      // only a getter, remove "final" modifier.
+      // TODO(paulberry): what if the getter and setter have a type mismatch?
+      throw new UnimplementedError();
+    }
+  }
+
+  /**
+   * Build the implicit top level variable associated with a getter or setter,
+   * and place it in [holder].
+   */
+  PropertyInducingElementImpl buildImplicitTopLevelVariable(
+      String name, UnlinkedExecutableKind kind, ElementHolder holder) {
+    if (holder.getTopLevelVariable(name) == null) {
+      TopLevelVariableElementImpl variable =
+          new TopLevelVariableElementImpl(name, -1);
+      variable.setModifier(Modifier.SYNTHETIC, true);
+      if (kind == UnlinkedExecutableKind.getter) {
+        variable.setModifier(Modifier.FINAL, true);
+      }
+      holder.addTopLevelVariable(variable);
+      return variable;
+    } else {
+      // TODO(paulberry): if adding a setter where there was previously
+      // only a getter, remove "final" modifier.
+      // TODO(paulberry): what if the getter and setter have a type mismatch?
+      throw new UnimplementedError();
+    }
+  }
+
+  /**
+   * Resynthesize an [ImportElement].
+   */
+  ImportElement buildImport(UnlinkedImport serializedImport, int dependency) {
+    bool isSynthetic = serializedImport.isImplicit;
+    // TODO(paulberry): it seems problematic for the offset to be 0 for
+    // non-synthetic imports, since it is used to disambiguate location.
+    ImportElementImpl importElement =
+        new ImportElementImpl(isSynthetic ? -1 : serializedImport.offset);
+    String absoluteUri = summaryResynthesizer.sourceFactory
+        .resolveUri(
+            librarySource, prelinkedLibrary.dependencies[dependency].uri)
+        .uri
+        .toString();
+    importElement.importedLibrary = new LibraryElementHandle(
+        summaryResynthesizer,
+        new ElementLocationImpl.con3(<String>[absoluteUri]));
+    if (isSynthetic) {
+      importElement.setModifier(Modifier.SYNTHETIC, true);
+    } else {
+      importElement.uri = serializedImport.uri;
+    }
+    if (serializedImport.prefixReference != 0) {
+      UnlinkedReference serializedPrefix = prelinkedLibrary.units[0]
+          .unlinked
+          .references[serializedImport.prefixReference];
+      importElement.prefix = new PrefixElementImpl(serializedPrefix.name, -1);
+    }
+    importElement.combinators =
+        serializedImport.combinators.map(buildCombinator).toList();
+    return importElement;
+  }
+
+  /**
+   * Main entry point.  Resynthesize the [LibraryElement] and return it.
+   */
+  LibraryElement buildLibrary() {
+    // TODO(paulberry): is it ok to pass -1 for offset and nameLength?
+    LibraryElementImpl libraryElement = new LibraryElementImpl(
+        summaryResynthesizer.context,
+        prelinkedLibrary.units[0].unlinked.libraryName,
+        -1,
+        -1);
+    CompilationUnitElementImpl definingCompilationUnit =
+        new CompilationUnitElementImpl(librarySource.shortName);
+    libraryElement.definingCompilationUnit = definingCompilationUnit;
+    definingCompilationUnit.source = librarySource;
+    definingCompilationUnit.librarySource = librarySource;
+    List<CompilationUnitElement> parts = <CompilationUnitElement>[];
+    UnlinkedUnit unlinkedDefiningUnit = prelinkedLibrary.units[0].unlinked;
+    assert(
+        unlinkedDefiningUnit.parts.length + 1 == prelinkedLibrary.units.length);
+    for (int i = 1; i < prelinkedLibrary.units.length; i++) {
+      CompilationUnitElementImpl part = buildPart(
+          unlinkedDefiningUnit.parts[i - 1].uri,
+          prelinkedLibrary.units[i].unlinked);
+      parts.add(part);
+    }
+    libraryElement.parts = parts;
+    List<ImportElement> imports = <ImportElement>[];
+    for (int i = 0; i < unlinkedDefiningUnit.imports.length; i++) {
+      imports.add(buildImport(unlinkedDefiningUnit.imports[i],
+          prelinkedLibrary.importDependencies[i]));
+    }
+    libraryElement.imports = imports;
+    libraryElement.exports =
+        unlinkedDefiningUnit.exports.map(buildExport).toList();
+    populateUnit(definingCompilationUnit, 0);
+    for (int i = 0; i < parts.length; i++) {
+      populateUnit(parts[i], i + 1);
+    }
+    return libraryElement;
+  }
+
+  /**
+   * Resynthesize a [ParameterElement].
+   */
+  ParameterElement buildParameter(UnlinkedParam serializedParameter) {
+    ParameterElementImpl parameterElement =
+        new ParameterElementImpl(serializedParameter.name, -1);
+    if (serializedParameter.isFunctionTyped) {
+      FunctionElementImpl parameterTypeElement =
+          new FunctionElementImpl('', -1);
+      parameterTypeElement.setModifier(Modifier.SYNTHETIC, true);
+      parameterElement.parameters =
+          serializedParameter.parameters.map(buildParameter).toList();
+      parameterTypeElement.enclosingElement = parameterElement;
+      parameterTypeElement.shareParameters(parameterElement.parameters);
+      if (serializedParameter.type != null) {
+        parameterTypeElement.returnType = buildType(serializedParameter.type);
+      } else {
+        parameterTypeElement.returnType = VoidTypeImpl.instance;
+      }
+      parameterElement.type = new FunctionTypeImpl(parameterTypeElement);
+    } else {
+      parameterElement.type = buildType(serializedParameter.type);
+      if (serializedParameter.hasImplicitType) {
+        parameterElement.setModifier(Modifier.IMPLICIT_TYPE, true);
+      }
+    }
+    switch (serializedParameter.kind) {
+      case UnlinkedParamKind.named:
+        parameterElement.parameterKind = ParameterKind.NAMED;
+        break;
+      case UnlinkedParamKind.positional:
+        parameterElement.parameterKind = ParameterKind.POSITIONAL;
+        break;
+      case UnlinkedParamKind.required:
+        parameterElement.parameterKind = ParameterKind.REQUIRED;
+        break;
+    }
+    return parameterElement;
+  }
+
+  /**
+   * Create, but do not populate, the [CompilationUnitElement] for a part other
+   * than the defining compilation unit.
+   */
+  CompilationUnitElementImpl buildPart(
+      String uri, UnlinkedUnit serializedPart) {
+    Source unitSource =
+        summaryResynthesizer.sourceFactory.resolveUri(librarySource, uri);
+    CompilationUnitElementImpl partUnit =
+        new CompilationUnitElementImpl(unitSource.shortName);
+    partUnit.source = unitSource;
+    partUnit.librarySource = librarySource;
+    partUnit.uri = uri;
+    return partUnit;
+  }
+
+  /**
+   * Build a [DartType] object based on an [UnlinkedTypeRef].  This [DartType]
+   * may refer to elements in other libraries than the library being
+   * deserialized, so handles are used to avoid having to deserialize other
+   * libraries in the process.
+   */
+  DartType buildType(UnlinkedTypeRef type) {
+    if (type.paramReference != 0) {
+      // TODO(paulberry): make this work for generic methods.
+      return currentTypeParameters[
+          currentTypeParameters.length - type.paramReference].type;
+    } else {
+      // TODO(paulberry): handle references to things other than classes (note:
+      // this should only occur in the case of erroneous code).
+      // TODO(paulberry): test reference to something inside a part.
+      // TODO(paulberry): test reference to something inside a part of the
+      // current lib.
+      UnlinkedReference reference =
+          prelinkedUnit.unlinked.references[type.reference];
+      PrelinkedReference referenceResolution =
+          prelinkedUnit.references[type.reference];
+      String referencedLibraryUri;
+      String partUri;
+      if (referenceResolution.dependency != 0) {
+        PrelinkedDependency dependency =
+            prelinkedLibrary.dependencies[referenceResolution.dependency];
+        Source referencedLibrarySource = summaryResynthesizer.sourceFactory
+            .resolveUri(librarySource, dependency.uri);
+        referencedLibraryUri = referencedLibrarySource.uri.toString();
+        PrelinkedLibrary referencedLibrary =
+            summaryResynthesizer.getSummary(referencedLibraryUri);
+        // TODO(paulberry): consider changing Location format so that this is
+        // not necessary (2nd string in location should just be the unit
+        // number).
+        if (referenceResolution.unit != 0) {
+          String uri = referencedLibrary.units[0].unlinked.parts[0].uri;
+          Source partSource = summaryResynthesizer.sourceFactory
+              .resolveUri(referencedLibrarySource, uri);
+          partUri = partSource.uri.toString();
+        } else {
+          partUri = referencedLibraryUri;
+        }
+      } else if (referenceResolution.kind ==
+          PrelinkedReferenceKind.unresolved) {
+        return summaryResynthesizer.typeProvider.undefinedType;
+      } else if (reference.name.isEmpty) {
+        return summaryResynthesizer.typeProvider.dynamicType;
+      } else {
+        referencedLibraryUri = librarySource.uri.toString();
+        if (referenceResolution.unit != 0) {
+          String uri = prelinkedLibrary.units[0].unlinked.parts[
+              referenceResolution.unit - 1].uri;
+          Source partSource =
+              summaryResynthesizer.sourceFactory.resolveUri(librarySource, uri);
+          partUri = partSource.uri.toString();
+        } else {
+          partUri = referencedLibraryUri;
+        }
+      }
+      ResynthesizedType resynthesizedType;
+      ElementLocationImpl location = new ElementLocationImpl.con3(
+          <String>[referencedLibraryUri, partUri, reference.name]);
+      switch (referenceResolution.kind) {
+        case PrelinkedReferenceKind.classOrEnum:
+          resynthesizedType = new ResynthesizedInterfaceTypeImpl(
+              new ClassElementHandle(summaryResynthesizer, location),
+              reference.name,
+              summaryResynthesizer);
+          break;
+        case PrelinkedReferenceKind.typedef:
+          resynthesizedType = new ResynthesizedFunctionTypeImpl(
+              new FunctionTypeAliasElementHandle(
+                  summaryResynthesizer, location),
+              reference.name,
+              summaryResynthesizer);
+          break;
+        default:
+          // TODO(paulberry): figure out how to handle this case (which should
+          // only occur in the event of erroneous code).
+          throw new UnimplementedError();
+      }
+      if (type.typeArguments.isNotEmpty) {
+        resynthesizedType._typeArguments =
+            type.typeArguments.map(buildType).toList();
+      }
+      return resynthesizedType;
+    }
+  }
+
+  /**
+   * Resynthesize a [FunctionTypeAliasElement] and place it in the
+   * [unitHolder].
+   */
+  void buildTypedef(UnlinkedTypedef serializedTypedef) {
+    try {
+      currentTypeParameters =
+          serializedTypedef.typeParameters.map(buildTypeParameter).toList();
+      for (int i = 0; i < serializedTypedef.typeParameters.length; i++) {
+        finishTypeParameter(
+            serializedTypedef.typeParameters[i], currentTypeParameters[i]);
+      }
+      FunctionTypeAliasElementImpl functionTypeAliasElement =
+          new FunctionTypeAliasElementImpl(serializedTypedef.name, -1);
+      functionTypeAliasElement.parameters =
+          serializedTypedef.parameters.map(buildParameter).toList();
+      if (serializedTypedef.returnType != null) {
+        functionTypeAliasElement.returnType =
+            buildType(serializedTypedef.returnType);
+      } else {
+        functionTypeAliasElement.returnType = VoidTypeImpl.instance;
+      }
+      functionTypeAliasElement.type =
+          new FunctionTypeImpl.forTypedef(functionTypeAliasElement);
+      functionTypeAliasElement.typeParameters = currentTypeParameters;
+      unitHolder.addTypeAlias(functionTypeAliasElement);
+    } finally {
+      currentTypeParameters = null;
+    }
+  }
+
+  /**
+   * Resynthesize a [TypeParameterElement], handling all parts of its except
+   * its bound.
+   *
+   * The bound is deferred until later since it may refer to other type
+   * parameters that have not been resynthesized yet.  To handle the bound,
+   * call [finishTypeParameter].
+   */
+  TypeParameterElement buildTypeParameter(
+      UnlinkedTypeParam serializedTypeParameter) {
+    TypeParameterElementImpl typeParameterElement =
+        new TypeParameterElementImpl(serializedTypeParameter.name, -1);
+    typeParameterElement.type = new TypeParameterTypeImpl(typeParameterElement);
+    return typeParameterElement;
+  }
+
+  /**
+   * Resynthesize a [TopLevelVariableElement] or [FieldElement].
+   */
+  void buildVariable(UnlinkedVariable serializedVariable,
+      [ElementHolder holder]) {
+    if (holder == null) {
+      TopLevelVariableElementImpl element =
+          new TopLevelVariableElementImpl(serializedVariable.name, -1);
+      buildVariableCommonParts(element, serializedVariable);
+      unitHolder.addTopLevelVariable(element);
+      buildImplicitAccessors(element, unitHolder);
+    } else {
+      FieldElementImpl element =
+          new FieldElementImpl(serializedVariable.name, -1);
+      buildVariableCommonParts(element, serializedVariable);
+      holder.addField(element);
+      buildImplicitAccessors(element, holder);
+    }
+  }
+
+  /**
+   * Handle the parts that are common to top level variables and fields.
+   */
+  void buildVariableCommonParts(PropertyInducingElementImpl element,
+      UnlinkedVariable serializedVariable) {
+    element.type = buildType(serializedVariable.type);
+    element.setModifier(Modifier.CONST, serializedVariable.isConst);
+    element.setModifier(Modifier.STATIC, serializedVariable.isStatic);
+  }
+
+  /**
+   * Finish creating a [TypeParameterElement] by deserializing its bound.
+   */
+  void finishTypeParameter(UnlinkedTypeParam serializedTypeParameter,
+      TypeParameterElementImpl typeParameterElement) {
+    if (serializedTypeParameter.bound != null) {
+      typeParameterElement.bound = buildType(serializedTypeParameter.bound);
+    }
+  }
+
+  /**
+   * Populate a [CompilationUnitElement] by deserializing all the elements
+   * contained in it.
+   */
+  void populateUnit(CompilationUnitElementImpl unit, int unitNum) {
+    prelinkedUnit = prelinkedLibrary.units[unitNum];
+    unitHolder = new ElementHolder();
+    UnlinkedUnit unlinkedUnit = prelinkedUnit.unlinked;
+    unlinkedUnit.classes.forEach(buildClass);
+    unlinkedUnit.enums.forEach(buildEnum);
+    unlinkedUnit.executables.forEach(buildExecutable);
+    unlinkedUnit.typedefs.forEach(buildTypedef);
+    unlinkedUnit.variables.forEach(buildVariable);
+    String absoluteUri = unit.source.uri.toString();
+    unit.accessors = unitHolder.accessors;
+    unit.enums = unitHolder.enums;
+    unit.functions = unitHolder.functions;
+    List<FunctionTypeAliasElement> typeAliases = unitHolder.typeAliases;
+    for (FunctionTypeAliasElementImpl typeAlias in typeAliases) {
+      if (typeAlias.isSynthetic) {
+        typeAlias.enclosingElement = unit;
+      }
+    }
+    unit.typeAliases = typeAliases.where((e) => !e.isSynthetic).toList();
+    unit.types = unitHolder.types;
+    unit.topLevelVariables = unitHolder.topLevelVariables;
+    Map<String, Element> elementMap = <String, Element>{};
+    for (ClassElement cls in unit.types) {
+      elementMap[cls.name] = cls;
+    }
+    for (ClassElement cls in unit.enums) {
+      elementMap[cls.name] = cls;
+    }
+    for (FunctionTypeAliasElement typeAlias in unit.functionTypeAliases) {
+      elementMap[typeAlias.name] = typeAlias;
+    }
+    resummarizedElements[absoluteUri] = elementMap;
+    unitHolder = null;
+    prelinkedUnit = null;
+  }
+}