pkg/analyzer/tool/task_dependency_graph/generate.dart - sdk.git - Git at Google

 // 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.

 /**
  * This file contains code to output a description of tasks and their
  * dependencies in ".dot" format.  Prior to running, the user should run "pub
  * get" in the analyzer directory to ensure that a "packages" folder exists.
  *
  * TODO(paulberry):
  * - Add general.dart and html.dart for completeness.
  * - Use Graphviz's "record" feature to produce more compact output
  *   (http://www.graphviz.org/content/node-shapes#record)
  * - Produce a warning if a result descriptor is found which isn't the output
  *   of exactly one task.
  * - Convert this tool to use package_config to find the package map.
  */
 library analyzer.tool.task_dependency_graph.generate;

 import 'dart:io' hide File;
 import 'dart:io' as io;

 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/physical_file_system.dart';
 import 'package:analyzer/src/codegen/tools.dart';
 import 'package:analyzer/src/generated/constant.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/java_io.dart';
 import 'package:analyzer/src/generated/sdk.dart';
 import 'package:analyzer/src/generated/sdk_io.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/generated/source_io.dart';
 import 'package:path/path.dart' as path;
 import 'package:path/path.dart';

 /**
  * Generate the target .dot file.
  */
 main() {
   String script = Platform.script.toFilePath(windows: Platform.isWindows);
   String pkgPath = normalize(join(dirname(script), '..', '..'));
   GeneratedContent.generateAll(pkgPath, <GeneratedContent>[target, htmlTarget]);
 }

 final GeneratedFile htmlTarget = new GeneratedFile(
     'doc/tasks.html', (String pkgPath) => new Driver(pkgPath).generateHtml());

 final GeneratedFile target = new GeneratedFile(
     'tool/task_dependency_graph/tasks.dot',
     (String pkgPath) => new Driver(pkgPath).generateFileContents());

 typedef void GetterFinderCallback(PropertyAccessorElement element);

 class Driver {
   static bool hasInitializedPlugins = false;
   PhysicalResourceProvider resourceProvider;
   AnalysisContext context;
   InterfaceType resultDescriptorType;
   InterfaceType listOfResultDescriptorType;
   ClassElement enginePluginClass;
   CompilationUnitElement taskUnitElement;
   InterfaceType extensionPointIdType;

   final String rootDir;

   Driver(String pkgPath) : rootDir = new Directory(pkgPath).absolute.path;

   /**
    * Get an [io.File] object corresponding to the file in which the generated
    * graph should be output.
    */
   io.File get file => new io.File(
       path.join(rootDir, 'tool', 'task_dependency_graph', 'tasks.dot'));

   /**
    * Starting at [node], find all calls to registerExtension() which refer to
    * the given [extensionIdVariable], and execute [callback] for the associated
    * result descriptors.
    */
   void findExtensions(AstNode node, TopLevelVariableElement extensionIdVariable,
       void callback(descriptorName)) {
     Set<PropertyAccessorElement> resultDescriptors =
         new Set<PropertyAccessorElement>();
     node.accept(new ExtensionFinder(
         resultDescriptorType, extensionIdVariable, resultDescriptors.add));
     for (PropertyAccessorElement resultDescriptor in resultDescriptors) {
       callback(resultDescriptor.name);
     }
   }

   /**
    * Starting at [node], find all references to a getter of type
    * `List<ResultDescriptor>`, and execute [callback] on the getter names.
    */
   void findResultDescriptorLists(
       AstNode node, void callback(String descriptorListName)) {
     Set<PropertyAccessorElement> resultDescriptorLists =
         new Set<PropertyAccessorElement>();
     node.accept(new GetterFinder(
         listOfResultDescriptorType, resultDescriptorLists.add));
     for (PropertyAccessorElement resultDescriptorList
         in resultDescriptorLists) {
       // We only care about result descriptor lists associated with getters in
       // the engine plugin class.
       if (resultDescriptorList.enclosingElement != enginePluginClass) {
         continue;
       }
       callback(resultDescriptorList.name);
     }
   }

   void findResultDescriptors(
       AstNode node, void callback(String descriptorName)) {
     Set<PropertyAccessorElement> resultDescriptors =
         new Set<PropertyAccessorElement>();
     node.accept(new GetterFinder(resultDescriptorType, resultDescriptors.add));
     for (PropertyAccessorElement resultDescriptor in resultDescriptors) {
       callback(resultDescriptor.name);
     }
   }

   /**
    * Generate the task dependency graph and return it as a [String].
    */
   String generateFileContents() {
     return '''
 // 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.
 //
 // This file has been automatically generated.  Please do not edit it manually.
 // To regenerate the file, use the script
 // "pkg/analyzer/tool/task_dependency_graph/generate.dart".
 //
 // To render this graph using Graphviz (www.graphviz.org) use the command:
 // "dot tasks.dot -Tpdf -O".
 digraph G {
 ${generateGraphData()}
 }
 ''';
   }

   String generateGraphData() {
     if (!hasInitializedPlugins) {
       AnalysisEngine.instance.processRequiredPlugins();
       hasInitializedPlugins = true;
     }
     List<String> lines = <String>[];
     resourceProvider = PhysicalResourceProvider.INSTANCE;
     DartSdk sdk = DirectoryBasedDartSdk.defaultSdk;
     context = AnalysisEngine.instance.createAnalysisContext();
     String packageRootPath;
     if (Platform.packageRoot != null) {
       packageRootPath = Uri.parse(Platform.packageRoot).toFilePath();
     } else {
       packageRootPath = path.join(rootDir, 'packages');
     }
     JavaFile packagesDir = new JavaFile(packageRootPath);
     List<UriResolver> uriResolvers = [
       new DartUriResolver(sdk),
       new PackageUriResolver(<JavaFile>[packagesDir]),
       new ResourceUriResolver(PhysicalResourceProvider.INSTANCE)
     ];
     context.sourceFactory = new SourceFactory(uriResolvers);
     Source dartDartSource =
         setupSource(path.join('lib', 'src', 'task', 'dart.dart'));
     Source taskSource = setupSource(path.join('lib', 'plugin', 'task.dart'));
     Source modelSource = setupSource(path.join('lib', 'task', 'model.dart'));
     Source enginePluginSource =
         setupSource(path.join('lib', 'src', 'plugin', 'engine_plugin.dart'));
     CompilationUnitElement modelElement = getUnit(modelSource).element;
     InterfaceType analysisTaskType = modelElement.getType('AnalysisTask').type;
     DartType dynamicType = context.typeProvider.dynamicType;
     resultDescriptorType = modelElement
         .getType('ResultDescriptor')
         .type
         .instantiate([dynamicType]);
     listOfResultDescriptorType =
         context.typeProvider.listType.instantiate([resultDescriptorType]);
     CompilationUnitElement enginePluginUnitElement =
         getUnit(enginePluginSource).element;
     enginePluginClass = enginePluginUnitElement.getType('EnginePlugin');
     extensionPointIdType =
         enginePluginUnitElement.getType('ExtensionPointId').type;
     CompilationUnit dartDartUnit = getUnit(dartDartSource);
     CompilationUnitElement dartDartUnitElement = dartDartUnit.element;
     CompilationUnit taskUnit = getUnit(taskSource);
     taskUnitElement = taskUnit.element;
     Set<String> results = new Set<String>();
     Set<String> resultLists = new Set<String>();
     for (ClassElement cls in dartDartUnitElement.types) {
       if (!cls.isAbstract && cls.type.isSubtypeOf(analysisTaskType)) {
         String task = cls.name;
         AstNode buildInputsAst = cls.getMethod('buildInputs').computeNode();
         findResultDescriptors(buildInputsAst, (String input) {
           results.add(input);
           lines.add('  $input -> $task');
         });
         findResultDescriptorLists(buildInputsAst, (String input) {
           resultLists.add(input);
           lines.add('  $input -> $task');
         });
         findResultDescriptors(cls.getField('DESCRIPTOR').computeNode(),
             (String out) {
           results.add(out);
           lines.add('  $task -> $out');
         });
       }
     }
     AstNode enginePluginAst = enginePluginUnitElement.computeNode();
     for (String resultList in resultLists) {
       lines.add('  $resultList [shape=hexagon]');
       TopLevelVariableElement extensionIdVariable = _getExtensionId(resultList);
       findExtensions(enginePluginAst, extensionIdVariable, (String extension) {
         results.add(extension);
         lines.add('  $extension -> $resultList');
       });
     }
     for (String result in results) {
       lines.add('  $result [shape=box]');
     }
     lines.sort();
     return lines.join('\n');
   }

   String generateHtml() {
     return '''
 <!DOCTYPE html>
 <html>
 <head>
     <title>Analysis Task Dependency Graph</title>
     <link rel="stylesheet" href="support/style.css">
     <script src="support/viz.js"></script>
     <script type="application/dart" src="support/web_app.dart.js"></script>
     <script src="support/dart.js"></script>
 </head>
 <body>
 <button id="zoomBtn">Zoom</button>
 <script type="text/vnd.graphviz" id="dot">
 digraph G {
   tooltip="Analysis Task Dependency Graph";
   node [fontname=Helvetica];
   edge [fontname=Helvetica, fontcolor=gray];
 ${generateGraphData()}
 }
 </script>
 </body>
 </html>
 ''';
   }

   CompilationUnit getUnit(Source source) =>
       context.resolveCompilationUnit2(source, source);

   Source setupSource(String filename) {
     String filePath = path.join(rootDir, filename);
     File file = resourceProvider.getResource(filePath);
     Source source = file.createSource();
     Uri restoredUri = context.sourceFactory.restoreUri(source);
     if (restoredUri != null) {
       source = file.createSource(restoredUri);
     }
     ChangeSet changeSet = new ChangeSet();
     changeSet.addedSource(source);
     context.applyChanges(changeSet);
     return source;
   }

   /**
    * Find the result list getter having name [resultListGetterName] in the
    * [EnginePlugin] class, and use the [ExtensionPointId] annotation on that
    * getter to find the associated [TopLevelVariableElement] which can be used
    * to register extensions for that getter.
    */
   TopLevelVariableElement _getExtensionId(String resultListGetterName) {
     PropertyAccessorElement getter =
         enginePluginClass.getGetter(resultListGetterName);
     for (ElementAnnotation annotation in getter.metadata) {
       DartObjectImpl annotationValue = annotation.constantValue;
       if (annotationValue.type.isSubtypeOf(extensionPointIdType)) {
         String extensionPointId =
             annotationValue.fields['extensionPointId'].toStringValue();
         for (TopLevelVariableElement variable
             in taskUnitElement.topLevelVariables) {
           if (variable.name == extensionPointId) {
             return variable;
           }
         }
       }
     }
     throw new Exception(
         'Could not find extension ID corresponding to $resultListGetterName');
   }
 }

 /**
  * Visitor that finds calls that register extension points.  Specifically, we
  * look for calls of the form `method(extensionIdVariable, resultDescriptor)`,
  * where `resultDescriptor` has type [resultDescriptorType], and we pass the
  * corresponding result descriptor names to [callback].
  */
 class ExtensionFinder extends GeneralizingAstVisitor {
   final InterfaceType resultDescriptorType;
   final TopLevelVariableElement extensionIdVariable;
   final GetterFinderCallback callback;

   ExtensionFinder(
       this.resultDescriptorType, this.extensionIdVariable, this.callback);

   @override
   visitIdentifier(Identifier node) {
     Element element = node.staticElement;
     if (element is PropertyAccessorElement &&
         element.isGetter &&
         element.variable == extensionIdVariable) {
       AstNode parent = node.parent;
       if (parent is ArgumentList &&
           parent.arguments.length == 2 &&
           parent.arguments[0] == node) {
         Expression extension = parent.arguments[1];
         if (extension is Identifier) {
           Element element = extension.staticElement;
           if (element is PropertyAccessorElement &&
               element.isGetter &&
               element.returnType.isSubtypeOf(resultDescriptorType)) {
             callback(element);
             return;
           }
         }
       }
       throw new Exception('Could not decode extension setup: $parent');
     }
   }
 }

 /**
  * Visitor that finds references to getters having a specific type (or a
  * subtype of that type)
  */
 class GetterFinder extends GeneralizingAstVisitor {
   final InterfaceType type;
   final GetterFinderCallback callback;

   GetterFinder(this.type, this.callback);

   @override
   visitIdentifier(Identifier node) {
     Element element = node.staticElement;
     if (element is PropertyAccessorElement &&
         element.isGetter &&
         element.returnType.isSubtypeOf(type)) {
       callback(element);
     }
   }
 }
	// 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.

	/**
	* This file contains code to output a description of tasks and their
	* dependencies in ".dot" format. Prior to running, the user should run "pub
	* get" in the analyzer directory to ensure that a "packages" folder exists.
	*
	* TODO(paulberry):
	* - Add general.dart and html.dart for completeness.
	* - Use Graphviz's "record" feature to produce more compact output
	* (http://www.graphviz.org/content/node-shapes#record)
	* - Produce a warning if a result descriptor is found which isn't the output
	* of exactly one task.
	* - Convert this tool to use package_config to find the package map.
	*/
	library analyzer.tool.task_dependency_graph.generate;

	import 'dart:io' hide File;
	import 'dart:io' as io;

	import 'package:analyzer/analyzer.dart';
	import 'package:analyzer/dart/element/element.dart';
	import 'package:analyzer/dart/element/type.dart';
	import 'package:analyzer/file_system/file_system.dart';
	import 'package:analyzer/file_system/physical_file_system.dart';
	import 'package:analyzer/src/codegen/tools.dart';
	import 'package:analyzer/src/generated/constant.dart';
	import 'package:analyzer/src/generated/engine.dart';
	import 'package:analyzer/src/generated/java_io.dart';
	import 'package:analyzer/src/generated/sdk.dart';
	import 'package:analyzer/src/generated/sdk_io.dart';
	import 'package:analyzer/src/generated/source.dart';
	import 'package:analyzer/src/generated/source_io.dart';
	import 'package:path/path.dart' as path;
	import 'package:path/path.dart';

	/**
	* Generate the target .dot file.
	*/
	main() {
	String script = Platform.script.toFilePath(windows: Platform.isWindows);
	String pkgPath = normalize(join(dirname(script), '..', '..'));
	GeneratedContent.generateAll(pkgPath, <GeneratedContent>[target, htmlTarget]);
	}

	final GeneratedFile htmlTarget = new GeneratedFile(
	'doc/tasks.html', (String pkgPath) => new Driver(pkgPath).generateHtml());

	final GeneratedFile target = new GeneratedFile(
	'tool/task_dependency_graph/tasks.dot',
	(String pkgPath) => new Driver(pkgPath).generateFileContents());

	typedef void GetterFinderCallback(PropertyAccessorElement element);

	class Driver {
	static bool hasInitializedPlugins = false;
	PhysicalResourceProvider resourceProvider;
	AnalysisContext context;
	InterfaceType resultDescriptorType;
	InterfaceType listOfResultDescriptorType;
	ClassElement enginePluginClass;
	CompilationUnitElement taskUnitElement;
	InterfaceType extensionPointIdType;

	final String rootDir;

	Driver(String pkgPath) : rootDir = new Directory(pkgPath).absolute.path;

	/**
	* Get an [io.File] object corresponding to the file in which the generated
	* graph should be output.
	*/
	io.File get file => new io.File(
	path.join(rootDir, 'tool', 'task_dependency_graph', 'tasks.dot'));

	/**
	* Starting at [node], find all calls to registerExtension() which refer to
	* the given [extensionIdVariable], and execute [callback] for the associated
	* result descriptors.
	*/
	void findExtensions(AstNode node, TopLevelVariableElement extensionIdVariable,
	void callback(descriptorName)) {
	Set<PropertyAccessorElement> resultDescriptors =
	new Set<PropertyAccessorElement>();
	node.accept(new ExtensionFinder(
	resultDescriptorType, extensionIdVariable, resultDescriptors.add));
	for (PropertyAccessorElement resultDescriptor in resultDescriptors) {
	callback(resultDescriptor.name);
	}
	}

	/**
	* Starting at [node], find all references to a getter of type
	* `List<ResultDescriptor>`, and execute [callback] on the getter names.
	*/
	void findResultDescriptorLists(
	AstNode node, void callback(String descriptorListName)) {
	Set<PropertyAccessorElement> resultDescriptorLists =
	new Set<PropertyAccessorElement>();
	node.accept(new GetterFinder(
	listOfResultDescriptorType, resultDescriptorLists.add));
	for (PropertyAccessorElement resultDescriptorList
	in resultDescriptorLists) {
	// We only care about result descriptor lists associated with getters in
	// the engine plugin class.
	if (resultDescriptorList.enclosingElement != enginePluginClass) {
	continue;
	}
	callback(resultDescriptorList.name);
	}
	}

	void findResultDescriptors(
	AstNode node, void callback(String descriptorName)) {
	Set<PropertyAccessorElement> resultDescriptors =
	new Set<PropertyAccessorElement>();
	node.accept(new GetterFinder(resultDescriptorType, resultDescriptors.add));
	for (PropertyAccessorElement resultDescriptor in resultDescriptors) {
	callback(resultDescriptor.name);
	}
	}

	/**
	* Generate the task dependency graph and return it as a [String].
	*/
	String generateFileContents() {
	return '''
	// 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.
	//
	// This file has been automatically generated. Please do not edit it manually.
	// To regenerate the file, use the script
	// "pkg/analyzer/tool/task_dependency_graph/generate.dart".
	//
	// To render this graph using Graphviz (www.graphviz.org) use the command:
	// "dot tasks.dot -Tpdf -O".
	digraph G {
	${generateGraphData()}
	}
	''';
	}

	String generateGraphData() {
	if (!hasInitializedPlugins) {
	AnalysisEngine.instance.processRequiredPlugins();
	hasInitializedPlugins = true;
	}
	List<String> lines = <String>[];
	resourceProvider = PhysicalResourceProvider.INSTANCE;
	DartSdk sdk = DirectoryBasedDartSdk.defaultSdk;
	context = AnalysisEngine.instance.createAnalysisContext();
	String packageRootPath;
	if (Platform.packageRoot != null) {
	packageRootPath = Uri.parse(Platform.packageRoot).toFilePath();
	} else {
	packageRootPath = path.join(rootDir, 'packages');
	}
	JavaFile packagesDir = new JavaFile(packageRootPath);
	List<UriResolver> uriResolvers = [
	new DartUriResolver(sdk),
	new PackageUriResolver(<JavaFile>[packagesDir]),
	new ResourceUriResolver(PhysicalResourceProvider.INSTANCE)
	];
	context.sourceFactory = new SourceFactory(uriResolvers);
	Source dartDartSource =
	setupSource(path.join('lib', 'src', 'task', 'dart.dart'));
	Source taskSource = setupSource(path.join('lib', 'plugin', 'task.dart'));
	Source modelSource = setupSource(path.join('lib', 'task', 'model.dart'));
	Source enginePluginSource =
	setupSource(path.join('lib', 'src', 'plugin', 'engine_plugin.dart'));
	CompilationUnitElement modelElement = getUnit(modelSource).element;
	InterfaceType analysisTaskType = modelElement.getType('AnalysisTask').type;
	DartType dynamicType = context.typeProvider.dynamicType;
	resultDescriptorType = modelElement
	.getType('ResultDescriptor')
	.type
	.instantiate([dynamicType]);
	listOfResultDescriptorType =
	context.typeProvider.listType.instantiate([resultDescriptorType]);
	CompilationUnitElement enginePluginUnitElement =
	getUnit(enginePluginSource).element;
	enginePluginClass = enginePluginUnitElement.getType('EnginePlugin');
	extensionPointIdType =
	enginePluginUnitElement.getType('ExtensionPointId').type;
	CompilationUnit dartDartUnit = getUnit(dartDartSource);
	CompilationUnitElement dartDartUnitElement = dartDartUnit.element;
	CompilationUnit taskUnit = getUnit(taskSource);
	taskUnitElement = taskUnit.element;
	Set<String> results = new Set<String>();
	Set<String> resultLists = new Set<String>();
	for (ClassElement cls in dartDartUnitElement.types) {
	if (!cls.isAbstract && cls.type.isSubtypeOf(analysisTaskType)) {
	String task = cls.name;
	AstNode buildInputsAst = cls.getMethod('buildInputs').computeNode();
	findResultDescriptors(buildInputsAst, (String input) {
	results.add(input);
	lines.add(' $input -> $task');
	});
	findResultDescriptorLists(buildInputsAst, (String input) {
	resultLists.add(input);
	lines.add(' $input -> $task');
	});
	findResultDescriptors(cls.getField('DESCRIPTOR').computeNode(),
	(String out) {
	results.add(out);
	lines.add(' $task -> $out');
	});
	}
	}
	AstNode enginePluginAst = enginePluginUnitElement.computeNode();
	for (String resultList in resultLists) {
	lines.add(' $resultList [shape=hexagon]');
	TopLevelVariableElement extensionIdVariable = _getExtensionId(resultList);
	findExtensions(enginePluginAst, extensionIdVariable, (String extension) {
	results.add(extension);
	lines.add(' $extension -> $resultList');
	});
	}
	for (String result in results) {
	lines.add(' $result [shape=box]');
	}
	lines.sort();
	return lines.join('\n');
	}

	String generateHtml() {
	return '''
	<!DOCTYPE html>
	<html>
	<head>
	<title>Analysis Task Dependency Graph</title>
	<link rel="stylesheet" href="support/style.css">
	<script src="support/viz.js"></script>
	<script type="application/dart" src="support/web_app.dart.js"></script>
	<script src="support/dart.js"></script>
	</head>
	<body>
	<button id="zoomBtn">Zoom</button>
	<script type="text/vnd.graphviz" id="dot">
	digraph G {
	tooltip="Analysis Task Dependency Graph";
	node [fontname=Helvetica];
	edge [fontname=Helvetica, fontcolor=gray];
	${generateGraphData()}
	}
	</script>
	</body>
	</html>
	''';
	}

	CompilationUnit getUnit(Source source) =>
	context.resolveCompilationUnit2(source, source);

	Source setupSource(String filename) {
	String filePath = path.join(rootDir, filename);
	File file = resourceProvider.getResource(filePath);
	Source source = file.createSource();
	Uri restoredUri = context.sourceFactory.restoreUri(source);
	if (restoredUri != null) {
	source = file.createSource(restoredUri);
	}
	ChangeSet changeSet = new ChangeSet();
	changeSet.addedSource(source);
	context.applyChanges(changeSet);
	return source;
	}

	/**
	* Find the result list getter having name [resultListGetterName] in the
	* [EnginePlugin] class, and use the [ExtensionPointId] annotation on that
	* getter to find the associated [TopLevelVariableElement] which can be used
	* to register extensions for that getter.
	*/
	TopLevelVariableElement _getExtensionId(String resultListGetterName) {
	PropertyAccessorElement getter =
	enginePluginClass.getGetter(resultListGetterName);
	for (ElementAnnotation annotation in getter.metadata) {
	DartObjectImpl annotationValue = annotation.constantValue;
	if (annotationValue.type.isSubtypeOf(extensionPointIdType)) {
	String extensionPointId =
	annotationValue.fields['extensionPointId'].toStringValue();
	for (TopLevelVariableElement variable
	in taskUnitElement.topLevelVariables) {
	if (variable.name == extensionPointId) {
	return variable;
	}
	}
	}
	}
	throw new Exception(
	'Could not find extension ID corresponding to $resultListGetterName');
	}
	}

	/**
	* Visitor that finds calls that register extension points. Specifically, we
	* look for calls of the form `method(extensionIdVariable, resultDescriptor)`,
	* where `resultDescriptor` has type [resultDescriptorType], and we pass the
	* corresponding result descriptor names to [callback].
	*/
	class ExtensionFinder extends GeneralizingAstVisitor {
	final InterfaceType resultDescriptorType;
	final TopLevelVariableElement extensionIdVariable;
	final GetterFinderCallback callback;

	ExtensionFinder(
	this.resultDescriptorType, this.extensionIdVariable, this.callback);

	@override
	visitIdentifier(Identifier node) {
	Element element = node.staticElement;
	if (element is PropertyAccessorElement &&
	element.isGetter &&
	element.variable == extensionIdVariable) {
	AstNode parent = node.parent;
	if (parent is ArgumentList &&
	parent.arguments.length == 2 &&
	parent.arguments[0] == node) {
	Expression extension = parent.arguments[1];
	if (extension is Identifier) {
	Element element = extension.staticElement;
	if (element is PropertyAccessorElement &&
	element.isGetter &&
	element.returnType.isSubtypeOf(resultDescriptorType)) {
	callback(element);
	return;
	}
	}
	}
	throw new Exception('Could not decode extension setup: $parent');
	}
	}
	}

	/**
	* Visitor that finds references to getters having a specific type (or a
	* subtype of that type)
	*/
	class GetterFinder extends GeneralizingAstVisitor {
	final InterfaceType type;
	final GetterFinderCallback callback;

	GetterFinder(this.type, this.callback);

	@override
	visitIdentifier(Identifier node) {
	Element element = node.staticElement;
	if (element is PropertyAccessorElement &&
	element.isGetter &&
	element.returnType.isSubtypeOf(type)) {
	callback(element);
	}
	}
	}