Move class DeclarationResolver to its own file.

pkg/analyzer/lib/src/generated/declaration_resolver.dart

+// Copyright (c) 2016, 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.generated.declaration_resolver;
+
+import 'dart:collection';
+
+import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/token.dart';
+import 'package:analyzer/dart/ast/visitor.dart';
+import 'package:analyzer/dart/element/element.dart';
+import 'package:analyzer/dart/element/visitor.dart';
+import 'package:analyzer/exception/exception.dart';
+import 'package:analyzer/src/dart/element/element.dart';
+
+/**
+ * A visitor that resolves declarations in an AST structure to already built
+ * elements.
+ *
+ * The resulting AST must have everything resolved that would have been resolved
+ * by a [CompilationUnitBuilder] (that is, must be a valid [RESOLVED_UNIT1]).
+ * This class must not assume that the [CompilationUnitElement] passed to it is
+ * any more complete than a [COMPILATION_UNIT_ELEMENT].
+ */
+class DeclarationResolver extends RecursiveAstVisitor<Object>
+    with _ExistingElementResolver {
+  /**
+   * The elements that are reachable from the compilation unit element. When a
+   * compilation unit has been resolved, this set should be empty.
+   */
+  Set<Element> _expectedElements;
+
+  /**
+   * The function type alias containing the AST nodes being visited, or `null`
+   * if we are not in the scope of a function type alias.
+   */
+  FunctionTypeAliasElement _enclosingAlias;
+
+  /**
+   * The class containing the AST nodes being visited, or `null` if we are not
+   * in the scope of a class.
+   */
+  ClassElement _enclosingClass;
+
+  /**
+   * The method or function containing the AST nodes being visited, or `null` if
+   * we are not in the scope of a method or function.
+   */
+  ExecutableElement _enclosingExecutable;
+
+  /**
+   * The parameter containing the AST nodes being visited, or `null` if we are
+   * not in the scope of a parameter.
+   */
+  ParameterElement _enclosingParameter;
+
+  /**
+   * Resolve the declarations within the given compilation [unit] to the
+   * elements rooted at the given [element]. Throw an [ElementMismatchException]
+   * if the element model and compilation unit do not match each other.
+   */
+  void resolve(CompilationUnit unit, CompilationUnitElement element) {
+    _ElementGatherer gatherer = new _ElementGatherer();
+    element.accept(gatherer);
+    _expectedElements = gatherer.elements;
+    _enclosingUnit = element;
+    _expectedElements.remove(element);
+    unit.element = element;
+    unit.accept(this);
+    _validateResolution();
+  }
+
+  @override
+  Object visitCatchClause(CatchClause node) {
+    SimpleIdentifier exceptionParameter = node.exceptionParameter;
+    if (exceptionParameter != null) {
+      List<LocalVariableElement> localVariables =
+          _enclosingExecutable.localVariables;
+      _findIdentifier(localVariables, exceptionParameter);
+      SimpleIdentifier stackTraceParameter = node.stackTraceParameter;
+      if (stackTraceParameter != null) {
+        _findIdentifier(localVariables, stackTraceParameter);
+      }
+    }
+    return super.visitCatchClause(node);
+  }
+
+  @override
+  Object visitClassDeclaration(ClassDeclaration node) {
+    ClassElement outerClass = _enclosingClass;
+    try {
+      SimpleIdentifier className = node.name;
+      _enclosingClass = _findIdentifier(_enclosingUnit.types, className);
+      super.visitClassDeclaration(node);
+      _resolveMetadata(node, node.metadata, _enclosingClass);
+      return null;
+    } finally {
+      _enclosingClass = outerClass;
+    }
+  }
+
+  @override
+  Object visitClassTypeAlias(ClassTypeAlias node) {
+    ClassElement outerClass = _enclosingClass;
+    try {
+      SimpleIdentifier className = node.name;
+      _enclosingClass = _findIdentifier(_enclosingUnit.types, className);
+      super.visitClassTypeAlias(node);
+      _resolveMetadata(node, node.metadata, _enclosingClass);
+      return null;
+    } finally {
+      _enclosingClass = outerClass;
+    }
+  }
+
+  @override
+  Object visitConstructorDeclaration(ConstructorDeclaration node) {
+    ExecutableElement outerExecutable = _enclosingExecutable;
+    try {
+      SimpleIdentifier constructorName = node.name;
+      if (constructorName == null) {
+        _enclosingExecutable = _enclosingClass.unnamedConstructor;
+        if (_enclosingExecutable == null) {
+          _mismatch('Could not find default constructor', node);
+        }
+      } else {
+        _enclosingExecutable =
+            _enclosingClass.getNamedConstructor(constructorName.name);
+        if (_enclosingExecutable == null) {
+          _mismatch(
+              'Could not find constructor element with name "${constructorName.name}',
+              node);
+        }
+        constructorName.staticElement = _enclosingExecutable;
+      }
+      _expectedElements.remove(_enclosingExecutable);
+      node.element = _enclosingExecutable as ConstructorElement;
+      super.visitConstructorDeclaration(node);
+      _resolveMetadata(node, node.metadata, _enclosingExecutable);
+      return null;
+    } finally {
+      _enclosingExecutable = outerExecutable;
+    }
+  }
+
+  @override
+  Object visitDeclaredIdentifier(DeclaredIdentifier node) {
+    SimpleIdentifier variableName = node.identifier;
+    Element element =
+        _findIdentifier(_enclosingExecutable.localVariables, variableName);
+    super.visitDeclaredIdentifier(node);
+    _resolveMetadata(node, node.metadata, element);
+    return null;
+  }
+
+  @override
+  Object visitDefaultFormalParameter(DefaultFormalParameter node) {
+    SimpleIdentifier parameterName = node.parameter.identifier;
+    ParameterElement element = _getElementForParameter(node, parameterName);
+    Expression defaultValue = node.defaultValue;
+    if (defaultValue != null) {
+      ExecutableElement outerExecutable = _enclosingExecutable;
+      try {
+        _enclosingExecutable = element.initializer;
+        defaultValue.accept(this);
+      } finally {
+        _enclosingExecutable = outerExecutable;
+      }
+    }
+    ParameterElement outerParameter = _enclosingParameter;
+    try {
+      _enclosingParameter = element;
+      super.visitDefaultFormalParameter(node);
+      _resolveMetadata(node, node.metadata, element);
+      return null;
+    } finally {
+      _enclosingParameter = outerParameter;
+    }
+  }
+
+  @override
+  Object visitEnumDeclaration(EnumDeclaration node) {
+    ClassElement enclosingEnum =
+        _findIdentifier(_enclosingUnit.enums, node.name);
+    List<FieldElement> constants = enclosingEnum.fields;
+    for (EnumConstantDeclaration constant in node.constants) {
+      _findIdentifier(constants, constant.name);
+    }
+    super.visitEnumDeclaration(node);
+    _resolveMetadata(node, node.metadata, enclosingEnum);
+    return null;
+  }
+
+  @override
+  Object visitExportDirective(ExportDirective node) {
+    super.visitExportDirective(node);
+    _resolveAnnotations(
+        node, node.metadata, _enclosingUnit.getAnnotations(node.offset));
+    return null;
+  }
+
+  @override
+  Object visitFieldDeclaration(FieldDeclaration node) {
+    super.visitFieldDeclaration(node);
+    _resolveMetadata(node, node.metadata, node.fields.variables[0].element);
+    return null;
+  }
+
+  @override
+  Object visitFieldFormalParameter(FieldFormalParameter node) {
+    if (node.parent is! DefaultFormalParameter) {
+      SimpleIdentifier parameterName = node.identifier;
+      ParameterElement element = _getElementForParameter(node, parameterName);
+      ParameterElement outerParameter = _enclosingParameter;
+      try {
+        _enclosingParameter = element;
+        super.visitFieldFormalParameter(node);
+        _resolveMetadata(node, node.metadata, element);
+        return null;
+      } finally {
+        _enclosingParameter = outerParameter;
+      }
+    } else {
+      return super.visitFieldFormalParameter(node);
+    }
+  }
+
+  @override
+  Object visitFunctionDeclaration(FunctionDeclaration node) {
+    ExecutableElement outerExecutable = _enclosingExecutable;
+    try {
+      SimpleIdentifier functionName = node.name;
+      Token property = node.propertyKeyword;
+      if (property == null) {
+        if (_enclosingExecutable != null) {
+          _enclosingExecutable =
+              _findIdentifier(_enclosingExecutable.functions, functionName);
+        } else {
+          _enclosingExecutable =
+              _findIdentifier(_enclosingUnit.functions, functionName);
+        }
+      } else {
+        if (_enclosingExecutable != null) {
+          _enclosingExecutable =
+              _findIdentifier(_enclosingExecutable.functions, functionName);
+        } else {
+          List<PropertyAccessorElement> accessors;
+          if (_enclosingClass != null) {
+            accessors = _enclosingClass.accessors;
+          } else {
+            accessors = _enclosingUnit.accessors;
+          }
+          PropertyAccessorElement accessor;
+          if (property.keyword == Keyword.GET) {
+            accessor = _findIdentifier(accessors, functionName);
+          } else if (property.keyword == Keyword.SET) {
+            accessor = _findWithNameAndOffset(accessors, functionName,
+                functionName.name + '=', functionName.offset);
+            _expectedElements.remove(accessor);
+            functionName.staticElement = accessor;
+          }
+          _enclosingExecutable = accessor;
+        }
+      }
+      node.functionExpression.element = _enclosingExecutable;
+      super.visitFunctionDeclaration(node);
+      _resolveMetadata(node, node.metadata, _enclosingExecutable);
+      return null;
+    } finally {
+      _enclosingExecutable = outerExecutable;
+    }
+  }
+
+  @override
+  Object visitFunctionExpression(FunctionExpression node) {
+    if (node.parent is! FunctionDeclaration) {
+      FunctionElement element = _findAtOffset(
+          _enclosingExecutable.functions, node, node.beginToken.offset);
+      _expectedElements.remove(element);
+      node.element = element;
+    }
+    ExecutableElement outerExecutable = _enclosingExecutable;
+    try {
+      _enclosingExecutable = node.element;
+      return super.visitFunctionExpression(node);
+    } finally {
+      _enclosingExecutable = outerExecutable;
+    }
+  }
+
+  @override
+  Object visitFunctionTypeAlias(FunctionTypeAlias node) {
+    FunctionTypeAliasElement outerAlias = _enclosingAlias;
+    try {
+      SimpleIdentifier aliasName = node.name;
+      _enclosingAlias =
+          _findIdentifier(_enclosingUnit.functionTypeAliases, aliasName);
+      super.visitFunctionTypeAlias(node);
+      _resolveMetadata(node, node.metadata, _enclosingAlias);
+      return null;
+    } finally {
+      _enclosingAlias = outerAlias;
+    }
+  }
+
+  @override
+  Object visitFunctionTypedFormalParameter(FunctionTypedFormalParameter node) {
+    if (node.parent is! DefaultFormalParameter) {
+      SimpleIdentifier parameterName = node.identifier;
+      ParameterElement element = _getElementForParameter(node, parameterName);
+      ParameterElement outerParameter = _enclosingParameter;
+      try {
+        _enclosingParameter = element;
+        super.visitFunctionTypedFormalParameter(node);
+        _resolveMetadata(node, node.metadata, _enclosingParameter);
+        return null;
+      } finally {
+        _enclosingParameter = outerParameter;
+      }
+    } else {
+      return super.visitFunctionTypedFormalParameter(node);
+    }
+  }
+
+  @override
+  Object visitImportDirective(ImportDirective node) {
+    super.visitImportDirective(node);
+    _resolveAnnotations(
+        node, node.metadata, _enclosingUnit.getAnnotations(node.offset));
+    return null;
+  }
+
+  @override
+  Object visitLabeledStatement(LabeledStatement node) {
+    for (Label label in node.labels) {
+      SimpleIdentifier labelName = label.label;
+      _findIdentifier(_enclosingExecutable.labels, labelName);
+    }
+    return super.visitLabeledStatement(node);
+  }
+
+  @override
+  Object visitLibraryDirective(LibraryDirective node) {
+    super.visitLibraryDirective(node);
+    _resolveAnnotations(
+        node, node.metadata, _enclosingUnit.getAnnotations(node.offset));
+    return null;
+  }
+
+  @override
+  Object visitMethodDeclaration(MethodDeclaration node) {
+    ExecutableElement outerExecutable = _enclosingExecutable;
+    try {
+      Token property = node.propertyKeyword;
+      SimpleIdentifier methodName = node.name;
+      String nameOfMethod = methodName.name;
+      if (property == null) {
+        String elementName = nameOfMethod == '-' &&
+                node.parameters != null &&
+                node.parameters.parameters.isEmpty
+            ? 'unary-'
+            : nameOfMethod;
+        _enclosingExecutable = _findWithNameAndOffset(_enclosingClass.methods,
+            methodName, elementName, methodName.offset);
+        _expectedElements.remove(_enclosingExecutable);
+        methodName.staticElement = _enclosingExecutable;
+      } else {
+        PropertyAccessorElement accessor;
+        if (property.keyword == Keyword.GET) {
+          accessor = _findIdentifier(_enclosingClass.accessors, methodName);
+        } else if (property.keyword == Keyword.SET) {
+          accessor = _findWithNameAndOffset(_enclosingClass.accessors,
+              methodName, nameOfMethod + '=', methodName.offset);
+          _expectedElements.remove(accessor);
+          methodName.staticElement = accessor;
+        }
+        _enclosingExecutable = accessor;
+      }
+      super.visitMethodDeclaration(node);
+      _resolveMetadata(node, node.metadata, _enclosingExecutable);
+      return null;
+    } finally {
+      _enclosingExecutable = outerExecutable;
+    }
+  }
+
+  @override
+  Object visitPartDirective(PartDirective node) {
+    super.visitPartDirective(node);
+    _resolveAnnotations(
+        node, node.metadata, _enclosingUnit.getAnnotations(node.offset));
+    return null;
+  }
+
+  @override
+  Object visitPartOfDirective(PartOfDirective node) {
+    node.element = _enclosingUnit.library;
+    return super.visitPartOfDirective(node);
+  }
+
+  @override
+  Object visitSimpleFormalParameter(SimpleFormalParameter node) {
+    if (node.parent is! DefaultFormalParameter) {
+      SimpleIdentifier parameterName = node.identifier;
+      ParameterElement element = _getElementForParameter(node, parameterName);
+      ParameterElement outerParameter = _enclosingParameter;
+      try {
+        _enclosingParameter = element;
+        super.visitSimpleFormalParameter(node);
+        _resolveMetadata(node, node.metadata, element);
+        return null;
+      } finally {
+        _enclosingParameter = outerParameter;
+      }
+    } else {}
+    return super.visitSimpleFormalParameter(node);
+  }
+
+  @override
+  Object visitSwitchCase(SwitchCase node) {
+    for (Label label in node.labels) {
+      SimpleIdentifier labelName = label.label;
+      _findIdentifier(_enclosingExecutable.labels, labelName);
+    }
+    return super.visitSwitchCase(node);
+  }
+
+  @override
+  Object visitSwitchDefault(SwitchDefault node) {
+    for (Label label in node.labels) {
+      SimpleIdentifier labelName = label.label;
+      _findIdentifier(_enclosingExecutable.labels, labelName);
+    }
+    return super.visitSwitchDefault(node);
+  }
+
+  @override
+  Object visitTopLevelVariableDeclaration(TopLevelVariableDeclaration node) {
+    super.visitTopLevelVariableDeclaration(node);
+    _resolveMetadata(node, node.metadata, node.variables.variables[0].element);
+    return null;
+  }
+
+  @override
+  Object visitTypeParameter(TypeParameter node) {
+    SimpleIdentifier parameterName = node.name;
+    Element element = null;
+    if (_enclosingExecutable != null) {
+      element = _findIdentifier(
+          _enclosingExecutable.typeParameters, parameterName,
+          required: false);
+    }
+    if (element == null) {
+      if (_enclosingClass != null) {
+        element =
+            _findIdentifier(_enclosingClass.typeParameters, parameterName);
+      } else if (_enclosingAlias != null) {
+        element =
+            _findIdentifier(_enclosingAlias.typeParameters, parameterName);
+      }
+    }
+    if (element == null) {
+      String name = parameterName.name;
+      int offset = parameterName.offset;
+      _mismatch(
+          'Could not find type parameter with name "$name" at $offset', node);
+    }
+    super.visitTypeParameter(node);
+    _resolveMetadata(node, node.metadata, element);
+    return null;
+  }
+
+  @override
+  Object visitVariableDeclaration(VariableDeclaration node) {
+    VariableElement element = null;
+    SimpleIdentifier variableName = node.name;
+    if (_enclosingExecutable != null) {
+      element = _findIdentifier(
+          _enclosingExecutable.localVariables, variableName,
+          required: false);
+    }
+    if (element == null && _enclosingClass != null) {
+      element = _findIdentifier(_enclosingClass.fields, variableName,
+          required: false);
+    }
+    if (element == null && _enclosingUnit != null) {
+      element = _findIdentifier(_enclosingUnit.topLevelVariables, variableName);
+    }
+    Expression initializer = node.initializer;
+    if (initializer != null) {
+      ExecutableElement outerExecutable = _enclosingExecutable;
+      try {
+        _enclosingExecutable = element.initializer;
+        return super.visitVariableDeclaration(node);
+      } finally {
+        _enclosingExecutable = outerExecutable;
+      }
+    }
+    return super.visitVariableDeclaration(node);
+  }
+
+  @override
+  Object visitVariableDeclarationList(VariableDeclarationList node) {
+    super.visitVariableDeclarationList(node);
+    if (node.parent is! FieldDeclaration &&
+        node.parent is! TopLevelVariableDeclaration) {
+      _resolveMetadata(node, node.metadata, node.variables[0].element);
+    }
+    return null;
+  }
+
+  /**
+   * Return the element in the given list of [elements] that was created for the
+   * declaration at the given [offset]. Throw an [ElementMismatchException] if
+   * an element at that offset cannot be found.
+   *
+   * This method should only be used when there is no name associated with the
+   * node.
+   */
+  Element _findAtOffset(List<Element> elements, AstNode node, int offset) =>
+      _findWithNameAndOffset(elements, node, '', offset);
+
+  /**
+   * Return the element in the given list of [elements] that was created for the
+   * declaration with the given [identifier]. As a side-effect, associate the
+   * returned element with the identifier. Throw an [ElementMismatchException]
+   * if an element corresponding to the identifier cannot be found unless
+   * [required] is `false`, in which case return `null`.
+   */
+  Element _findIdentifier(List<Element> elements, SimpleIdentifier identifier,
+      {bool required: true}) {
+    Element element = _findWithNameAndOffset(
+        elements, identifier, identifier.name, identifier.offset,
+        required: required);
+    _expectedElements.remove(element);
+    identifier.staticElement = element;
+    return element;
+  }
+
+  /**
+   * Return the element in the given list of [elements] that was created for the
+   * declaration with the given [name] at the given [offset]. Throw an
+   * [ElementMismatchException] if an element corresponding to the identifier
+   * cannot be found unless [required] is `false`, in which case return `null`.
+   */
+  Element _findWithNameAndOffset(
+      List<Element> elements, AstNode node, String name, int offset,
+      {bool required: true}) {
+    int length = elements.length;
+    for (int i = 0; i < length; i++) {
+      Element element = elements[i];
+      if (element.nameOffset == offset && element.name == name) {
+        return element;
+      }
+    }
+    if (!required) {
+      return null;
+    }
+    for (int i = 0; i < length; i++) {
+      Element element = elements[i];
+      if (element.name == name) {
+        _mismatch(
+            'Found element with name "$name" at ${element.nameOffset}, '
+            'but expected offset of $offset',
+            node);
+      }
+      if (element.nameOffset == offset) {
+        _mismatch(
+            'Found element with name "${element.name}" at $offset, '
+            'but expected element with name "$name"',
+            node);
+      }
+    }
+    _mismatch('Could not find element with name "$name" at $offset', node);
+    return null; // Never reached
+  }
+
+  /**
+   * Search the most closely enclosing list of parameter elements for a
+   * parameter, defined by the given [node], with the given [parameterName].
+   * Return the element that was found, or throw an [ElementMismatchException]
+   * if an element corresponding to the identifier cannot be found.
+   */
+  ParameterElement _getElementForParameter(
+      FormalParameter node, SimpleIdentifier parameterName) {
+    List<ParameterElement> parameters = null;
+    if (_enclosingParameter != null) {
+      parameters = _enclosingParameter.parameters;
+    }
+    if (parameters == null && _enclosingExecutable != null) {
+      parameters = _enclosingExecutable.parameters;
+    }
+    if (parameters == null && _enclosingAlias != null) {
+      parameters = _enclosingAlias.parameters;
+    }
+    if (parameters == null) {
+      StringBuffer buffer = new StringBuffer();
+      buffer.writeln('Could not find parameter in enclosing scope');
+      buffer.writeln(
+          '(_enclosingParameter == null) == ${_enclosingParameter == null}');
+      buffer.writeln(
+          '(_enclosingExecutable == null) == ${_enclosingExecutable == null}');
+      buffer.writeln('(_enclosingAlias == null) == ${_enclosingAlias == null}');
+      _mismatch(buffer.toString(), parameterName);
+    }
+    return _findIdentifier(parameters, parameterName);
+  }
+
+  /**
+   * Associate each of the annotation [nodes] with the corresponding
+   * [ElementAnnotation] in [annotations]. If there is a problem, report it
+   * against the given [parent] node.
+   */
+  void _resolveAnnotations(AstNode parent, NodeList<Annotation> nodes,
+      List<ElementAnnotation> annotations) {
+    int nodeCount = nodes.length;
+    if (nodeCount != annotations.length) {
+      _mismatch(
+          'Found $nodeCount annotation nodes and '
+          '${annotations.length} element annotations',
+          parent);
+    }
+    for (int i = 0; i < nodeCount; i++) {
+      nodes[i].elementAnnotation = annotations[i];
+    }
+  }
+
+  /**
+   * If [element] is not `null`, associate each of the annotation [nodes] with
+   * the corresponding [ElementAnnotation] in [element.metadata]. If there is a
+   * problem, report it against the given [parent] node.
+   *
+   * If [element] is `null`, do nothing--this allows us to be robust in the
+   * case where we are operating on an element model that hasn't been fully
+   * built.
+   */
+  void _resolveMetadata(
+      AstNode parent, NodeList<Annotation> nodes, Element element) {
+    if (element != null) {
+      _resolveAnnotations(parent, nodes, element.metadata);
+    }
+  }
+
+  /**
+   * Throw an exception if there are non-synthetic elements in the element model
+   * that were not associated with an AST node.
+   */
+  void _validateResolution() {
+    if (_expectedElements.isNotEmpty) {
+      StringBuffer buffer = new StringBuffer();
+      buffer.write(_expectedElements.length);
+      buffer.writeln(' unmatched elements found:');
+      for (Element element in _expectedElements) {
+        buffer.write('  ');
+        buffer.writeln(element);
+      }
+      throw new _ElementMismatchException(buffer.toString());
+    }
+  }
+}
+
+/**
+ * A visitor that can be used to collect all of the non-synthetic elements in an
+ * element model.
+ */
+class _ElementGatherer extends GeneralizingElementVisitor {
+  /**
+   * The set in which the elements are collected.
+   */
+  final Set<Element> elements = new HashSet<Element>();
+
+  /**
+   * Initialize the visitor.
+   */
+  _ElementGatherer();
+
+  @override
+  void visitElement(Element element) {
+    if (!element.isSynthetic) {
+      elements.add(element);
+    }
+    super.visitElement(element);
+  }
+}
+
+class _ElementMismatchException extends AnalysisException {
+  /**
+   * Initialize a newly created exception to have the given [message] and
+   * [cause].
+   */
+  _ElementMismatchException(String message, [CaughtException cause = null])
+      : super(message, cause);
+}
+
+/**
+ * A mixin for classes that use an existing element model to resolve a portion
+ * of an AST structure.
+ */
+class _ExistingElementResolver {
+  /**
+   * The compilation unit containing the AST nodes being visited.
+   */
+  CompilationUnitElementImpl _enclosingUnit;
+
+  /**
+   * Throw an [ElementMismatchException] to report that the element model and the
+   * AST do not match. The [message] will have the path to the given [node]
+   * appended to it.
+   */
+  void _mismatch(String message, AstNode node) {
+    StringBuffer buffer = new StringBuffer();
+    buffer.write('Mismatch in ');
+    buffer.write(runtimeType);
+    buffer.write(' while resolving ');
+    buffer.writeln(_enclosingUnit?.source?.fullName);
+    buffer.writeln(message);
+    buffer.write('Path to root:');
+    String separator = ' ';
+    AstNode parent = node;
+    while (parent != null) {
+      buffer.write(separator);
+      buffer.write(parent.runtimeType.toString());
+      separator = ', ';
+      parent = parent.parent;
+    }
+    throw new _ElementMismatchException(buffer.toString());
+  }
+}