packages/flutter_tools/lib/src/compile.dart - mirrors/flutter - Git at Google

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 import 'dart:async';
 import 'dart:convert';

 import 'package:meta/meta.dart';
 import 'package:usage/uuid/uuid.dart';

 import 'artifacts.dart';
 import 'base/common.dart';
 import 'base/context.dart';
 import 'base/file_system.dart';
 import 'base/fingerprint.dart';
 import 'base/io.dart';
 import 'base/platform.dart';
 import 'base/process_manager.dart';
 import 'base/terminal.dart';
 import 'dart/package_map.dart';
 import 'globals.dart';

 KernelCompiler get kernelCompiler => context[KernelCompiler];

 typedef CompilerMessageConsumer = void Function(String message, {bool emphasis, TerminalColor color});

 /// The target model describes the set of core libraries that are availible within
 /// the SDK.
 class TargetModel {
   /// Parse a [TargetModel] from a raw string.
   ///
   /// Throws an [AssertionError] if passed a value other than 'flutter' or
   /// 'flutter_runner'.
   factory TargetModel(String rawValue) {
     switch (rawValue) {
       case 'flutter':
         return flutter;
       case 'flutter_runner':
         return flutterRunner;
     }
     assert(false);
     return null;
   }

   const TargetModel._(this._value);

   /// The flutter patched dart SDK
   static const TargetModel flutter = TargetModel._('flutter');

   /// The fuchsia patched SDK.
   static const TargetModel flutterRunner = TargetModel._('flutter_runner');

   final String _value;

   @override
   String toString() => _value;
 }

 class CompilerOutput {
   const CompilerOutput(this.outputFilename, this.errorCount);

   final String outputFilename;
   final int errorCount;
 }

 class _StdoutHandler {
   _StdoutHandler({this.consumer = printError}) {
     reset();
   }

   bool compilerMessageReceived = false;
   final CompilerMessageConsumer consumer;
   String boundaryKey;
   Completer<CompilerOutput> compilerOutput;

   bool _suppressCompilerMessages;

   void handler(String message) {
     const String kResultPrefix = 'result ';
     if (boundaryKey == null) {
       if (message.startsWith(kResultPrefix))
         boundaryKey = message.substring(kResultPrefix.length);
     } else if (message.startsWith(boundaryKey)) {
       if (message.length <= boundaryKey.length) {
         compilerOutput.complete(null);
         return;
       }
       final int spaceDelimiter = message.lastIndexOf(' ');
       compilerOutput.complete(
         CompilerOutput(
           message.substring(boundaryKey.length + 1, spaceDelimiter),
           int.parse(message.substring(spaceDelimiter + 1).trim())));
     }
     else if (!_suppressCompilerMessages) {
       if (compilerMessageReceived == false) {
         consumer('\nCompiler message:');
         compilerMessageReceived = true;
       }
       consumer(message);
     }
   }

   // This is needed to get ready to process next compilation result output,
   // with its own boundary key and new completer.
   void reset({bool suppressCompilerMessages = false}) {
     boundaryKey = null;
     compilerMessageReceived = false;
     compilerOutput = Completer<CompilerOutput>();
     _suppressCompilerMessages = suppressCompilerMessages;
   }
 }

 // Converts filesystem paths to package URIs.
 class _PackageUriMapper {
   _PackageUriMapper(String scriptPath, String packagesPath) {
     final Map<String, Uri> packageMap = PackageMap(fs.path.absolute(packagesPath)).map;
     final String scriptUri = Uri.file(scriptPath, windows: platform.isWindows).toString();

     for (String packageName in packageMap.keys) {
       final String prefix = packageMap[packageName].toString();
       if (scriptUri.startsWith(prefix)) {
         _packageName = packageName;
         _uriPrefix = prefix;
         return;
       }
     }
   }

   String _packageName;
   String _uriPrefix;

   Uri map(String scriptPath) {
     if (_packageName == null)
       return null;

     final String scriptUri = Uri.file(scriptPath, windows: platform.isWindows).toString();
     if (scriptUri.startsWith(_uriPrefix)) {
       return Uri.parse('package:$_packageName/${scriptUri.substring(_uriPrefix.length)}');
     }

     return null;
   }

   static Uri findUri(String scriptPath, String packagesPath) {
     return _PackageUriMapper(scriptPath, packagesPath).map(scriptPath);
   }
 }

 class KernelCompiler {
   const KernelCompiler();

   Future<CompilerOutput> compile({
     String sdkRoot,
     String mainPath,
     String outputFilePath,
     String depFilePath,
     TargetModel targetModel = TargetModel.flutter,
     bool linkPlatformKernelIn = false,
     bool aot = false,
     @required bool trackWidgetCreation,
     List<String> extraFrontEndOptions,
     String incrementalCompilerByteStorePath,
     String packagesPath,
     List<String> fileSystemRoots,
     String fileSystemScheme,
     bool targetProductVm = false,
   }) async {
     final String frontendServer = artifacts.getArtifactPath(
       Artifact.frontendServerSnapshotForEngineDartSdk
     );

     // TODO(cbracken): eliminate pathFilter.
     // Currently the compiler emits buildbot paths for the core libs in the
     // depfile. None of these are available on the local host.
     Fingerprinter fingerprinter;
     if (depFilePath != null) {
       fingerprinter = Fingerprinter(
         fingerprintPath: '$depFilePath.fingerprint',
         paths: <String>[mainPath],
         properties: <String, String>{
           'entryPoint': mainPath,
           'trackWidgetCreation': trackWidgetCreation.toString(),
           'linkPlatformKernelIn': linkPlatformKernelIn.toString(),
         },
         depfilePaths: <String>[depFilePath],
         pathFilter: (String path) => !path.startsWith('/b/build/slave/'),
       );

       if (await fingerprinter.doesFingerprintMatch()) {
         printTrace('Skipping kernel compilation. Fingerprint match.');
         return CompilerOutput(outputFilePath, 0);
       }
     }

     // This is a URI, not a file path, so the forward slash is correct even on Windows.
     if (!sdkRoot.endsWith('/'))
       sdkRoot = '$sdkRoot/';
     final String engineDartPath = artifacts.getArtifactPath(Artifact.engineDartBinary);
     if (!processManager.canRun(engineDartPath)) {
       throwToolExit('Unable to find Dart binary at $engineDartPath');
     }
     final List<String> command = <String>[
       engineDartPath,
       frontendServer,
       '--sdk-root',
       sdkRoot,
       '--strong',
       '--target=$targetModel',
     ];
     if (trackWidgetCreation)
       command.add('--track-widget-creation');
     if (!linkPlatformKernelIn)
       command.add('--no-link-platform');
     if (aot) {
       command.add('--aot');
       command.add('--tfa');
     }
     if (targetProductVm) {
       command.add('-Ddart.vm.product=true');
     }
     if (incrementalCompilerByteStorePath != null) {
       command.add('--incremental');
     }
     Uri mainUri;
     if (packagesPath != null) {
       command.addAll(<String>['--packages', packagesPath]);
        mainUri = _PackageUriMapper.findUri(mainPath, packagesPath);
     }
     if (outputFilePath != null) {
       command.addAll(<String>['--output-dill', outputFilePath]);
     }
     if (depFilePath != null && (fileSystemRoots == null || fileSystemRoots.isEmpty)) {
       command.addAll(<String>['--depfile', depFilePath]);
     }
     if (fileSystemRoots != null) {
       for (String root in fileSystemRoots) {
         command.addAll(<String>['--filesystem-root', root]);
       }
     }
     if (fileSystemScheme != null) {
       command.addAll(<String>['--filesystem-scheme', fileSystemScheme]);
     }

     if (extraFrontEndOptions != null)
       command.addAll(extraFrontEndOptions);

     command.add(mainUri?.toString() ?? mainPath);

     printTrace(command.join(' '));
     final Process server = await processManager
         .start(command)
         .catchError((dynamic error, StackTrace stack) {
       printError('Failed to start frontend server $error, $stack');
     });

     final _StdoutHandler _stdoutHandler = _StdoutHandler();

     server.stderr
       .transform<String>(utf8.decoder)
       .listen((String message) { printError(message); });
     server.stdout
       .transform<String>(utf8.decoder)
       .transform<String>(const LineSplitter())
       .listen(_stdoutHandler.handler);
     final int exitCode = await server.exitCode;
     if (exitCode == 0) {
       if (fingerprinter != null) {
         await fingerprinter.writeFingerprint();
       }
       return _stdoutHandler.compilerOutput.future;
     }
     return null;
   }
 }

 /// Class that allows to serialize compilation requests to the compiler.
 abstract class _CompilationRequest {
   _CompilationRequest(this.completer);

   Completer<CompilerOutput> completer;

   Future<CompilerOutput> _run(ResidentCompiler compiler);

   Future<void> run(ResidentCompiler compiler) async {
     completer.complete(await _run(compiler));
   }
 }

 class _RecompileRequest extends _CompilationRequest {
   _RecompileRequest(Completer<CompilerOutput> completer, this.mainPath,
       this.invalidatedFiles, this.outputPath, this.packagesFilePath) :
       super(completer);

   String mainPath;
   List<String> invalidatedFiles;
   String outputPath;
   String packagesFilePath;

   @override
   Future<CompilerOutput> _run(ResidentCompiler compiler) async =>
       compiler._recompile(this);
 }

 class _CompileExpressionRequest extends _CompilationRequest {
   _CompileExpressionRequest(Completer<CompilerOutput> completer, this.expression, this.definitions,
       this.typeDefinitions, this.libraryUri, this.klass, this.isStatic) :
       super(completer);

   String expression;
   List<String> definitions;
   List<String> typeDefinitions;
   String libraryUri;
   String klass;
   bool isStatic;

   @override
   Future<CompilerOutput> _run(ResidentCompiler compiler) async =>
       compiler._compileExpression(this);
 }

 /// Wrapper around incremental frontend server compiler, that communicates with
 /// server via stdin/stdout.
 ///
 /// The wrapper is intended to stay resident in memory as user changes, reloads,
 /// restarts the Flutter app.
 class ResidentCompiler {
   ResidentCompiler(this._sdkRoot, {
     bool trackWidgetCreation = false,
     String packagesPath,
     List<String> fileSystemRoots,
     String fileSystemScheme,
     CompilerMessageConsumer compilerMessageConsumer = printError,
     String initializeFromDill,
     TargetModel targetModel = TargetModel.flutter,
     bool unsafePackageSerialization
   }) : assert(_sdkRoot != null),
        _trackWidgetCreation = trackWidgetCreation,
        _packagesPath = packagesPath,
        _fileSystemRoots = fileSystemRoots,
        _fileSystemScheme = fileSystemScheme,
        _targetModel = targetModel,
        _stdoutHandler = _StdoutHandler(consumer: compilerMessageConsumer),
        _controller = StreamController<_CompilationRequest>(),
        _initializeFromDill = initializeFromDill,
        _unsafePackageSerialization = unsafePackageSerialization {
     // This is a URI, not a file path, so the forward slash is correct even on Windows.
     if (!_sdkRoot.endsWith('/'))
       _sdkRoot = '$_sdkRoot/';
   }

   final bool _trackWidgetCreation;
   final String _packagesPath;
   final TargetModel _targetModel;
   final List<String> _fileSystemRoots;
   final String _fileSystemScheme;
   String _sdkRoot;
   Process _server;
   final _StdoutHandler _stdoutHandler;
   String _initializeFromDill;
   bool _unsafePackageSerialization;

   final StreamController<_CompilationRequest> _controller;

   /// If invoked for the first time, it compiles Dart script identified by
   /// [mainPath], [invalidatedFiles] list is ignored.
   /// On successive runs [invalidatedFiles] indicates which files need to be
   /// recompiled. If [mainPath] is [null], previously used [mainPath] entry
   /// point that is used for recompilation.
   /// Binary file name is returned if compilation was successful, otherwise
   /// null is returned.
   Future<CompilerOutput> recompile(String mainPath, List<String> invalidatedFiles,
       {@required String outputPath, String packagesFilePath}) async {
     assert (outputPath != null);
     if (!_controller.hasListener) {
       _controller.stream.listen(_handleCompilationRequest);
     }

     final Completer<CompilerOutput> completer = Completer<CompilerOutput>();
     _controller.add(
         _RecompileRequest(completer, mainPath, invalidatedFiles, outputPath, packagesFilePath)
     );
     return completer.future;
   }

   Future<CompilerOutput> _recompile(_RecompileRequest request) async {
     _stdoutHandler.reset();

     // First time recompile is called we actually have to compile the app from
     // scratch ignoring list of invalidated files.
     _PackageUriMapper packageUriMapper;
     if (request.packagesFilePath != null) {
       packageUriMapper = _PackageUriMapper(request.mainPath, request.packagesFilePath);
     }

     if (_server == null) {
       return _compile(
           _mapFilename(request.mainPath, packageUriMapper),
           request.outputPath,
           _mapFilename(request.packagesFilePath, /* packageUriMapper= */ null)
       );
     }

     final String inputKey = Uuid().generateV4();
     final String mainUri = request.mainPath != null
         ? _mapFilename(request.mainPath, packageUriMapper) + ' '
         : '';
     _server.stdin.writeln('recompile $mainUri$inputKey');
     for (String fileUri in request.invalidatedFiles) {
       _server.stdin.writeln(_mapFileUri(fileUri, packageUriMapper));
     }
     _server.stdin.writeln(inputKey);

     return _stdoutHandler.compilerOutput.future;
   }

   final List<_CompilationRequest> _compilationQueue = <_CompilationRequest>[];

   Future<void> _handleCompilationRequest(_CompilationRequest request) async {
     final bool isEmpty = _compilationQueue.isEmpty;
     _compilationQueue.add(request);
     // Only trigger processing if queue was empty - i.e. no other requests
     // are currently being processed. This effectively enforces "one
     // compilation request at a time".
     if (isEmpty) {
       while (_compilationQueue.isNotEmpty) {
         final _CompilationRequest request = _compilationQueue.first;
         await request.run(this);
         _compilationQueue.removeAt(0);
       }
     }
   }

   Future<CompilerOutput> _compile(String scriptUri, String outputPath,
       String packagesFilePath) async {
     final String frontendServer = artifacts.getArtifactPath(
       Artifact.frontendServerSnapshotForEngineDartSdk
     );
     final List<String> command = <String>[
       artifacts.getArtifactPath(Artifact.engineDartBinary),
       frontendServer,
       '--sdk-root',
       _sdkRoot,
       '--incremental',
       '--strong',
       '--target=$_targetModel',
     ];
     if (outputPath != null) {
       command.addAll(<String>['--output-dill', outputPath]);
     }
     if (packagesFilePath != null) {
       command.addAll(<String>['--packages', packagesFilePath]);
     }
     if (_trackWidgetCreation) {
       command.add('--track-widget-creation');
     }
     if (_packagesPath != null) {
       command.addAll(<String>['--packages', _packagesPath]);
     }
     if (_fileSystemRoots != null) {
       for (String root in _fileSystemRoots) {
         command.addAll(<String>['--filesystem-root', root]);
       }
     }
     if (_fileSystemScheme != null) {
       command.addAll(<String>['--filesystem-scheme', _fileSystemScheme]);
     }
     if (_initializeFromDill != null) {
       command.addAll(<String>['--initialize-from-dill', _initializeFromDill]);
     }
     if (_unsafePackageSerialization == true) {
       command.add('--unsafe-package-serialization');
     }
     printTrace(command.join(' '));
     _server = await processManager.start(command);
     _server.stdout
       .transform<String>(utf8.decoder)
       .transform<String>(const LineSplitter())
       .listen(
         _stdoutHandler.handler,
         onDone: () {
           // when outputFilename future is not completed, but stdout is closed
           // process has died unexpectedly.
           if (!_stdoutHandler.compilerOutput.isCompleted) {
             _stdoutHandler.compilerOutput.complete(null);
           }
         });

     _server.stderr
       .transform<String>(utf8.decoder)
       .transform<String>(const LineSplitter())
       .listen((String message) { printError(message); });

     _server.stdin.writeln('compile $scriptUri');

     return _stdoutHandler.compilerOutput.future;
   }

   Future<CompilerOutput> compileExpression(String expression, List<String> definitions,
       List<String> typeDefinitions, String libraryUri, String klass, bool isStatic) {
     if (!_controller.hasListener) {
       _controller.stream.listen(_handleCompilationRequest);
     }

     final Completer<CompilerOutput> completer = Completer<CompilerOutput>();
     _controller.add(
         _CompileExpressionRequest(
             completer, expression, definitions, typeDefinitions, libraryUri, klass, isStatic)
     );
     return completer.future;
   }

   Future<CompilerOutput> _compileExpression(
       _CompileExpressionRequest request) async {
     _stdoutHandler.reset(suppressCompilerMessages: true);

     // 'compile-expression' should be invoked after compiler has been started,
     // program was compiled.
     if (_server == null)
       return null;

     final String inputKey = Uuid().generateV4();
     _server.stdin.writeln('compile-expression $inputKey');
     _server.stdin.writeln(request.expression);
     request.definitions?.forEach(_server.stdin.writeln);
     _server.stdin.writeln(inputKey);
     request.typeDefinitions?.forEach(_server.stdin.writeln);
     _server.stdin.writeln(inputKey);
     _server.stdin.writeln(request.libraryUri ?? '');
     _server.stdin.writeln(request.klass ?? '');
     _server.stdin.writeln(request.isStatic ?? false);

     return _stdoutHandler.compilerOutput.future;
   }

   /// Should be invoked when results of compilation are accepted by the client.
   ///
   /// Either [accept] or [reject] should be called after every [recompile] call.
   void accept() {
     _server.stdin.writeln('accept');
   }

   /// Should be invoked when results of compilation are rejected by the client.
   ///
   /// Either [accept] or [reject] should be called after every [recompile] call.
   void reject() {
     _server.stdin.writeln('reject');
   }

   /// Should be invoked when frontend server compiler should forget what was
   /// accepted previously so that next call to [recompile] produces complete
   /// kernel file.
   void reset() {
     _server?.stdin?.writeln('reset');
   }

   String _mapFilename(String filename, _PackageUriMapper packageUriMapper) {
     return _doMapFilename(filename, packageUriMapper) ?? filename;
   }

   String _mapFileUri(String fileUri, _PackageUriMapper packageUriMapper) {
     String filename;
     try {
       filename = Uri.parse(fileUri).toFilePath();
     } on UnsupportedError catch (_) {
       return fileUri;
     }
     return _doMapFilename(filename, packageUriMapper) ?? fileUri;
   }

   String _doMapFilename(String filename, _PackageUriMapper packageUriMapper) {
     if (packageUriMapper != null) {
       final Uri packageUri = packageUriMapper.map(filename);
       if (packageUri != null)
         return packageUri.toString();
     }

     if (_fileSystemRoots != null) {
       for (String root in _fileSystemRoots) {
         if (filename.startsWith(root)) {
           return Uri(
               scheme: _fileSystemScheme, path: filename.substring(root.length))
               .toString();
         }
       }
     }
     return null;
   }

   Future<dynamic> shutdown() {
     _server.kill();
     return _server.exitCode;
   }
 }
	// Copyright 2017 The Chromium Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	import 'dart:async';
	import 'dart:convert';

	import 'package:meta/meta.dart';
	import 'package:usage/uuid/uuid.dart';

	import 'artifacts.dart';
	import 'base/common.dart';
	import 'base/context.dart';
	import 'base/file_system.dart';
	import 'base/fingerprint.dart';
	import 'base/io.dart';
	import 'base/platform.dart';
	import 'base/process_manager.dart';
	import 'base/terminal.dart';
	import 'dart/package_map.dart';
	import 'globals.dart';

	KernelCompiler get kernelCompiler => context[KernelCompiler];

	typedef CompilerMessageConsumer = void Function(String message, {bool emphasis, TerminalColor color});

	/// The target model describes the set of core libraries that are availible within
	/// the SDK.
	class TargetModel {
	/// Parse a [TargetModel] from a raw string.
	///
	/// Throws an [AssertionError] if passed a value other than 'flutter' or
	/// 'flutter_runner'.
	factory TargetModel(String rawValue) {
	switch (rawValue) {
	case 'flutter':
	return flutter;
	case 'flutter_runner':
	return flutterRunner;
	}
	assert(false);
	return null;
	}

	const TargetModel._(this._value);

	/// The flutter patched dart SDK
	static const TargetModel flutter = TargetModel._('flutter');

	/// The fuchsia patched SDK.
	static const TargetModel flutterRunner = TargetModel._('flutter_runner');

	final String _value;

	@override
	String toString() => _value;
	}

	class CompilerOutput {
	const CompilerOutput(this.outputFilename, this.errorCount);

	final String outputFilename;
	final int errorCount;
	}

	class _StdoutHandler {
	_StdoutHandler({this.consumer = printError}) {
	reset();
	}

	bool compilerMessageReceived = false;
	final CompilerMessageConsumer consumer;
	String boundaryKey;
	Completer<CompilerOutput> compilerOutput;

	bool _suppressCompilerMessages;

	void handler(String message) {
	const String kResultPrefix = 'result ';
	if (boundaryKey == null) {
	if (message.startsWith(kResultPrefix))
	boundaryKey = message.substring(kResultPrefix.length);
	} else if (message.startsWith(boundaryKey)) {
	if (message.length <= boundaryKey.length) {
	compilerOutput.complete(null);
	return;
	}
	final int spaceDelimiter = message.lastIndexOf(' ');
	compilerOutput.complete(
	CompilerOutput(
	message.substring(boundaryKey.length + 1, spaceDelimiter),
	int.parse(message.substring(spaceDelimiter + 1).trim())));
	}
	else if (!_suppressCompilerMessages) {
	if (compilerMessageReceived == false) {
	consumer('\nCompiler message:');
	compilerMessageReceived = true;
	}
	consumer(message);
	}
	}

	// This is needed to get ready to process next compilation result output,
	// with its own boundary key and new completer.
	void reset({bool suppressCompilerMessages = false}) {
	boundaryKey = null;
	compilerMessageReceived = false;
	compilerOutput = Completer<CompilerOutput>();
	_suppressCompilerMessages = suppressCompilerMessages;
	}
	}

	// Converts filesystem paths to package URIs.
	class _PackageUriMapper {
	_PackageUriMapper(String scriptPath, String packagesPath) {
	final Map<String, Uri> packageMap = PackageMap(fs.path.absolute(packagesPath)).map;
	final String scriptUri = Uri.file(scriptPath, windows: platform.isWindows).toString();

	for (String packageName in packageMap.keys) {
	final String prefix = packageMap[packageName].toString();
	if (scriptUri.startsWith(prefix)) {
	_packageName = packageName;
	_uriPrefix = prefix;
	return;
	}
	}
	}

	String _packageName;
	String _uriPrefix;

	Uri map(String scriptPath) {
	if (_packageName == null)
	return null;

	final String scriptUri = Uri.file(scriptPath, windows: platform.isWindows).toString();
	if (scriptUri.startsWith(_uriPrefix)) {
	return Uri.parse('package:$_packageName/${scriptUri.substring(_uriPrefix.length)}');
	}

	return null;
	}

	static Uri findUri(String scriptPath, String packagesPath) {
	return _PackageUriMapper(scriptPath, packagesPath).map(scriptPath);
	}
	}

	class KernelCompiler {
	const KernelCompiler();

	Future<CompilerOutput> compile({
	String sdkRoot,
	String mainPath,
	String outputFilePath,
	String depFilePath,
	TargetModel targetModel = TargetModel.flutter,
	bool linkPlatformKernelIn = false,
	bool aot = false,
	@required bool trackWidgetCreation,
	List<String> extraFrontEndOptions,
	String incrementalCompilerByteStorePath,
	String packagesPath,
	List<String> fileSystemRoots,
	String fileSystemScheme,
	bool targetProductVm = false,
	}) async {
	final String frontendServer = artifacts.getArtifactPath(
	Artifact.frontendServerSnapshotForEngineDartSdk
	);

	// TODO(cbracken): eliminate pathFilter.
	// Currently the compiler emits buildbot paths for the core libs in the
	// depfile. None of these are available on the local host.
	Fingerprinter fingerprinter;
	if (depFilePath != null) {
	fingerprinter = Fingerprinter(
	fingerprintPath: '$depFilePath.fingerprint',
	paths: <String>[mainPath],
	properties: <String, String>{
	'entryPoint': mainPath,
	'trackWidgetCreation': trackWidgetCreation.toString(),
	'linkPlatformKernelIn': linkPlatformKernelIn.toString(),
	},
	depfilePaths: <String>[depFilePath],
	pathFilter: (String path) => !path.startsWith('/b/build/slave/'),
	);

	if (await fingerprinter.doesFingerprintMatch()) {
	printTrace('Skipping kernel compilation. Fingerprint match.');
	return CompilerOutput(outputFilePath, 0);
	}
	}

	// This is a URI, not a file path, so the forward slash is correct even on Windows.
	if (!sdkRoot.endsWith('/'))
	sdkRoot = '$sdkRoot/';
	final String engineDartPath = artifacts.getArtifactPath(Artifact.engineDartBinary);
	if (!processManager.canRun(engineDartPath)) {
	throwToolExit('Unable to find Dart binary at $engineDartPath');
	}
	final List<String> command = <String>[
	engineDartPath,
	frontendServer,
	'--sdk-root',
	sdkRoot,
	'--strong',
	'--target=$targetModel',
	];
	if (trackWidgetCreation)
	command.add('--track-widget-creation');
	if (!linkPlatformKernelIn)
	command.add('--no-link-platform');
	if (aot) {
	command.add('--aot');
	command.add('--tfa');
	}
	if (targetProductVm) {
	command.add('-Ddart.vm.product=true');
	}
	if (incrementalCompilerByteStorePath != null) {
	command.add('--incremental');
	}
	Uri mainUri;
	if (packagesPath != null) {
	command.addAll(<String>['--packages', packagesPath]);
	mainUri = _PackageUriMapper.findUri(mainPath, packagesPath);
	}
	if (outputFilePath != null) {
	command.addAll(<String>['--output-dill', outputFilePath]);
	}
	if (depFilePath != null && (fileSystemRoots == null \|\| fileSystemRoots.isEmpty)) {
	command.addAll(<String>['--depfile', depFilePath]);
	}
	if (fileSystemRoots != null) {
	for (String root in fileSystemRoots) {
	command.addAll(<String>['--filesystem-root', root]);
	}
	}
	if (fileSystemScheme != null) {
	command.addAll(<String>['--filesystem-scheme', fileSystemScheme]);
	}

	if (extraFrontEndOptions != null)
	command.addAll(extraFrontEndOptions);

	command.add(mainUri?.toString() ?? mainPath);

	printTrace(command.join(' '));
	final Process server = await processManager
	.start(command)
	.catchError((dynamic error, StackTrace stack) {
	printError('Failed to start frontend server $error, $stack');
	});

	final _StdoutHandler _stdoutHandler = _StdoutHandler();

	server.stderr
	.transform<String>(utf8.decoder)
	.listen((String message) { printError(message); });
	server.stdout
	.transform<String>(utf8.decoder)
	.transform<String>(const LineSplitter())
	.listen(_stdoutHandler.handler);
	final int exitCode = await server.exitCode;
	if (exitCode == 0) {
	if (fingerprinter != null) {
	await fingerprinter.writeFingerprint();
	}
	return _stdoutHandler.compilerOutput.future;
	}
	return null;
	}
	}

	/// Class that allows to serialize compilation requests to the compiler.
	abstract class _CompilationRequest {
	_CompilationRequest(this.completer);

	Completer<CompilerOutput> completer;

	Future<CompilerOutput> _run(ResidentCompiler compiler);

	Future<void> run(ResidentCompiler compiler) async {
	completer.complete(await _run(compiler));
	}
	}

	class _RecompileRequest extends _CompilationRequest {
	_RecompileRequest(Completer<CompilerOutput> completer, this.mainPath,
	this.invalidatedFiles, this.outputPath, this.packagesFilePath) :
	super(completer);

	String mainPath;
	List<String> invalidatedFiles;
	String outputPath;
	String packagesFilePath;

	@override
	Future<CompilerOutput> _run(ResidentCompiler compiler) async =>
	compiler._recompile(this);
	}

	class _CompileExpressionRequest extends _CompilationRequest {
	_CompileExpressionRequest(Completer<CompilerOutput> completer, this.expression, this.definitions,
	this.typeDefinitions, this.libraryUri, this.klass, this.isStatic) :
	super(completer);

	String expression;
	List<String> definitions;
	List<String> typeDefinitions;
	String libraryUri;
	String klass;
	bool isStatic;

	@override
	Future<CompilerOutput> _run(ResidentCompiler compiler) async =>
	compiler._compileExpression(this);
	}

	/// Wrapper around incremental frontend server compiler, that communicates with
	/// server via stdin/stdout.
	///
	/// The wrapper is intended to stay resident in memory as user changes, reloads,
	/// restarts the Flutter app.
	class ResidentCompiler {
	ResidentCompiler(this._sdkRoot, {
	bool trackWidgetCreation = false,
	String packagesPath,
	List<String> fileSystemRoots,
	String fileSystemScheme,
	CompilerMessageConsumer compilerMessageConsumer = printError,
	String initializeFromDill,
	TargetModel targetModel = TargetModel.flutter,
	bool unsafePackageSerialization
	}) : assert(_sdkRoot != null),
	_trackWidgetCreation = trackWidgetCreation,
	_packagesPath = packagesPath,
	_fileSystemRoots = fileSystemRoots,
	_fileSystemScheme = fileSystemScheme,
	_targetModel = targetModel,
	_stdoutHandler = _StdoutHandler(consumer: compilerMessageConsumer),
	_controller = StreamController<_CompilationRequest>(),
	_initializeFromDill = initializeFromDill,
	_unsafePackageSerialization = unsafePackageSerialization {
	// This is a URI, not a file path, so the forward slash is correct even on Windows.
	if (!_sdkRoot.endsWith('/'))
	_sdkRoot = '$_sdkRoot/';
	}

	final bool _trackWidgetCreation;
	final String _packagesPath;
	final TargetModel _targetModel;
	final List<String> _fileSystemRoots;
	final String _fileSystemScheme;
	String _sdkRoot;
	Process _server;
	final _StdoutHandler _stdoutHandler;
	String _initializeFromDill;
	bool _unsafePackageSerialization;

	final StreamController<_CompilationRequest> _controller;

	/// If invoked for the first time, it compiles Dart script identified by
	/// [mainPath], [invalidatedFiles] list is ignored.
	/// On successive runs [invalidatedFiles] indicates which files need to be
	/// recompiled. If [mainPath] is [null], previously used [mainPath] entry
	/// point that is used for recompilation.
	/// Binary file name is returned if compilation was successful, otherwise
	/// null is returned.
	Future<CompilerOutput> recompile(String mainPath, List<String> invalidatedFiles,
	{@required String outputPath, String packagesFilePath}) async {
	assert (outputPath != null);
	if (!_controller.hasListener) {
	_controller.stream.listen(_handleCompilationRequest);
	}

	final Completer<CompilerOutput> completer = Completer<CompilerOutput>();
	_controller.add(
	_RecompileRequest(completer, mainPath, invalidatedFiles, outputPath, packagesFilePath)
	);
	return completer.future;
	}

	Future<CompilerOutput> _recompile(_RecompileRequest request) async {
	_stdoutHandler.reset();

	// First time recompile is called we actually have to compile the app from
	// scratch ignoring list of invalidated files.
	_PackageUriMapper packageUriMapper;
	if (request.packagesFilePath != null) {
	packageUriMapper = _PackageUriMapper(request.mainPath, request.packagesFilePath);
	}

	if (_server == null) {
	return _compile(
	_mapFilename(request.mainPath, packageUriMapper),
	request.outputPath,
	_mapFilename(request.packagesFilePath, /* packageUriMapper= */ null)
	);
	}

	final String inputKey = Uuid().generateV4();
	final String mainUri = request.mainPath != null
	? _mapFilename(request.mainPath, packageUriMapper) + ' '
	: '';
	_server.stdin.writeln('recompile $mainUri$inputKey');
	for (String fileUri in request.invalidatedFiles) {
	_server.stdin.writeln(_mapFileUri(fileUri, packageUriMapper));
	}
	_server.stdin.writeln(inputKey);

	return _stdoutHandler.compilerOutput.future;
	}

	final List<_CompilationRequest> _compilationQueue = <_CompilationRequest>[];

	Future<void> _handleCompilationRequest(_CompilationRequest request) async {
	final bool isEmpty = _compilationQueue.isEmpty;
	_compilationQueue.add(request);
	// Only trigger processing if queue was empty - i.e. no other requests
	// are currently being processed. This effectively enforces "one
	// compilation request at a time".
	if (isEmpty) {
	while (_compilationQueue.isNotEmpty) {
	final _CompilationRequest request = _compilationQueue.first;
	await request.run(this);
	_compilationQueue.removeAt(0);
	}
	}
	}

	Future<CompilerOutput> _compile(String scriptUri, String outputPath,
	String packagesFilePath) async {
	final String frontendServer = artifacts.getArtifactPath(
	Artifact.frontendServerSnapshotForEngineDartSdk
	);
	final List<String> command = <String>[
	artifacts.getArtifactPath(Artifact.engineDartBinary),
	frontendServer,
	'--sdk-root',
	_sdkRoot,
	'--incremental',
	'--strong',
	'--target=$_targetModel',
	];
	if (outputPath != null) {
	command.addAll(<String>['--output-dill', outputPath]);
	}
	if (packagesFilePath != null) {
	command.addAll(<String>['--packages', packagesFilePath]);
	}
	if (_trackWidgetCreation) {
	command.add('--track-widget-creation');
	}
	if (_packagesPath != null) {
	command.addAll(<String>['--packages', _packagesPath]);
	}
	if (_fileSystemRoots != null) {
	for (String root in _fileSystemRoots) {
	command.addAll(<String>['--filesystem-root', root]);
	}
	}
	if (_fileSystemScheme != null) {
	command.addAll(<String>['--filesystem-scheme', _fileSystemScheme]);
	}
	if (_initializeFromDill != null) {
	command.addAll(<String>['--initialize-from-dill', _initializeFromDill]);
	}
	if (_unsafePackageSerialization == true) {
	command.add('--unsafe-package-serialization');
	}
	printTrace(command.join(' '));
	_server = await processManager.start(command);
	_server.stdout
	.transform<String>(utf8.decoder)
	.transform<String>(const LineSplitter())
	.listen(
	_stdoutHandler.handler,
	onDone: () {
	// when outputFilename future is not completed, but stdout is closed
	// process has died unexpectedly.
	if (!_stdoutHandler.compilerOutput.isCompleted) {
	_stdoutHandler.compilerOutput.complete(null);
	}
	});

	_server.stderr
	.transform<String>(utf8.decoder)
	.transform<String>(const LineSplitter())
	.listen((String message) { printError(message); });

	_server.stdin.writeln('compile $scriptUri');

	return _stdoutHandler.compilerOutput.future;
	}

	Future<CompilerOutput> compileExpression(String expression, List<String> definitions,
	List<String> typeDefinitions, String libraryUri, String klass, bool isStatic) {
	if (!_controller.hasListener) {
	_controller.stream.listen(_handleCompilationRequest);
	}

	final Completer<CompilerOutput> completer = Completer<CompilerOutput>();
	_controller.add(
	_CompileExpressionRequest(
	completer, expression, definitions, typeDefinitions, libraryUri, klass, isStatic)
	);
	return completer.future;
	}

	Future<CompilerOutput> _compileExpression(
	_CompileExpressionRequest request) async {
	_stdoutHandler.reset(suppressCompilerMessages: true);

	// 'compile-expression' should be invoked after compiler has been started,
	// program was compiled.
	if (_server == null)
	return null;

	final String inputKey = Uuid().generateV4();
	_server.stdin.writeln('compile-expression $inputKey');
	_server.stdin.writeln(request.expression);
	request.definitions?.forEach(_server.stdin.writeln);
	_server.stdin.writeln(inputKey);
	request.typeDefinitions?.forEach(_server.stdin.writeln);
	_server.stdin.writeln(inputKey);
	_server.stdin.writeln(request.libraryUri ?? '');
	_server.stdin.writeln(request.klass ?? '');
	_server.stdin.writeln(request.isStatic ?? false);

	return _stdoutHandler.compilerOutput.future;
	}

	/// Should be invoked when results of compilation are accepted by the client.
	///
	/// Either [accept] or [reject] should be called after every [recompile] call.
	void accept() {
	_server.stdin.writeln('accept');
	}

	/// Should be invoked when results of compilation are rejected by the client.
	///
	/// Either [accept] or [reject] should be called after every [recompile] call.
	void reject() {
	_server.stdin.writeln('reject');
	}

	/// Should be invoked when frontend server compiler should forget what was
	/// accepted previously so that next call to [recompile] produces complete
	/// kernel file.
	void reset() {
	_server?.stdin?.writeln('reset');
	}

	String _mapFilename(String filename, _PackageUriMapper packageUriMapper) {
	return _doMapFilename(filename, packageUriMapper) ?? filename;
	}

	String _mapFileUri(String fileUri, _PackageUriMapper packageUriMapper) {
	String filename;
	try {
	filename = Uri.parse(fileUri).toFilePath();
	} on UnsupportedError catch (_) {
	return fileUri;
	}
	return _doMapFilename(filename, packageUriMapper) ?? fileUri;
	}

	String _doMapFilename(String filename, _PackageUriMapper packageUriMapper) {
	if (packageUriMapper != null) {
	final Uri packageUri = packageUriMapper.map(filename);
	if (packageUri != null)
	return packageUri.toString();
	}

	if (_fileSystemRoots != null) {
	for (String root in _fileSystemRoots) {
	if (filename.startsWith(root)) {
	return Uri(
	scheme: _fileSystemScheme, path: filename.substring(root.length))
	.toString();
	}
	}
	}
	return null;
	}

	Future<dynamic> shutdown() {
	_server.kill();
	return _server.exitCode;
	}
	}