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

 // Copyright 2016 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 '../android/android_sdk.dart';
 import '../artifacts.dart';
 import '../base/build.dart';
 import '../base/common.dart';
 import '../base/file_system.dart';
 import '../base/logger.dart';
 import '../base/process.dart';
 import '../base/utils.dart';
 import '../build_info.dart';
 import '../compile.dart';
 import '../dart/package_map.dart';
 import '../globals.dart';
 import '../resident_runner.dart';
 import '../runner/flutter_command.dart';
 import 'build.dart';

 // Files generated by the ahead-of-time snapshot builder.
 const List<String> kAotSnapshotFiles = const <String>[
   'vm_snapshot_data', 'vm_snapshot_instr', 'isolate_snapshot_data', 'isolate_snapshot_instr',
 ];

 class BuildAotCommand extends BuildSubCommand {
   BuildAotCommand({bool verboseHelp: false}) {
     usesTargetOption();
     addBuildModeFlags();
     usesPubOption();
     argParser
       ..addOption('output-dir', defaultsTo: getAotBuildDirectory())
       ..addOption('target-platform',
         defaultsTo: 'android-arm',
         allowed: <String>['android-arm', 'android-arm64', 'ios']
       )
       ..addFlag('interpreter')
       ..addFlag('quiet', defaultsTo: false)
       ..addFlag('preview-dart-2',
         defaultsTo: true,
         hide: !verboseHelp,
         help: 'Preview Dart 2.0 functionality.',
       )
       ..addMultiOption(FlutterOptions.kExtraFrontEndOptions,
         splitCommas: true,
         hide: true,
       )
       ..addMultiOption(FlutterOptions.kExtraGenSnapshotOptions,
         splitCommas: true,
         hide: true,
       )
       ..addFlag('prefer-shared-library',
         negatable: false,
         help: 'Whether to prefer compiling to a *.so file (android only).');
   }

   @override
   final String name = 'aot';

   @override
   final String description = "Build an ahead-of-time compiled snapshot of your app's Dart code.";

   @override
   Future<Null> runCommand() async {
     await super.runCommand();
     final String targetPlatform = argResults['target-platform'];
     final TargetPlatform platform = getTargetPlatformForName(targetPlatform);
     if (platform == null)
       throwToolExit('Unknown platform: $targetPlatform');

     final String typeName = artifacts.getEngineType(platform, getBuildMode());
     Status status;
     if (!argResults['quiet']) {
       status = logger.startProgress('Building AOT snapshot in ${getModeName(getBuildMode())} mode ($typeName)...',
           expectSlowOperation: true);
     }
     final String outputPath = await buildAotSnapshot(
       findMainDartFile(targetFile),
       platform,
       getBuildMode(),
       outputPath: argResults['output-dir'],
       interpreter: argResults['interpreter'],
       previewDart2: argResults['preview-dart-2'],
       extraFrontEndOptions: argResults[FlutterOptions.kExtraFrontEndOptions],
       extraGenSnapshotOptions: argResults[FlutterOptions.kExtraGenSnapshotOptions],
       preferSharedLibrary: argResults['prefer-shared-library'],
     );
     status?.stop();

     if (outputPath == null)
       throwToolExit(null);

     final String builtMessage = 'Built to $outputPath${fs.path.separator}.';
     if (argResults['quiet']) {
       printTrace(builtMessage);
     } else {
       printStatus(builtMessage);
     }
   }
 }

 String _getPackagePath(PackageMap packageMap, String package) {
   return fs.path.dirname(packageMap.map[package].toFilePath());
 }

 /// Build an AOT snapshot. Return null (and log to `printError`) if the method
 /// fails.
 Future<String> buildAotSnapshot(
   String mainPath,
   TargetPlatform platform,
   BuildMode buildMode, {
   String outputPath,
   bool interpreter: false,
   bool previewDart2: false,
   List<String> extraFrontEndOptions,
   List<String> extraGenSnapshotOptions,
   bool preferSharedLibrary: false,
 }) async {
   outputPath ??= getAotBuildDirectory();
   try {
     return _buildAotSnapshot(
       mainPath,
       platform,
       buildMode,
       outputPath: outputPath,
       interpreter: interpreter,
       previewDart2: previewDart2,
       extraFrontEndOptions: extraFrontEndOptions,
       extraGenSnapshotOptions: extraGenSnapshotOptions,
       preferSharedLibrary: preferSharedLibrary,
     );
   } on String catch (error) {
     // Catch the String exceptions thrown from the `runCheckedSync` methods below.
     printError(error);
     return null;
   }
 }

 // TODO(cbracken): split AOT and Assembly AOT snapshotting logic and migrate to Snapshotter class.
 Future<String> _buildAotSnapshot(
   String mainPath,
   TargetPlatform platform,
   BuildMode buildMode, {
   String outputPath,
   bool interpreter: false,
   bool previewDart2: false,
   List<String> extraFrontEndOptions,
   List<String> extraGenSnapshotOptions,
   bool preferSharedLibrary: false,
 }) async {
   outputPath ??= getAotBuildDirectory();
   if (!isAotBuildMode(buildMode) && !interpreter) {
     printError('${toTitleCase(getModeName(buildMode))} mode does not support AOT compilation.');
     return null;
   }

   if (!(platform == TargetPlatform.android_arm ||
         platform == TargetPlatform.android_arm64 ||
         platform == TargetPlatform.ios)) {
     printError('${getNameForTargetPlatform(platform)} does not support AOT compilation.');
     return null;
   }

   final Directory outputDir = fs.directory(outputPath);
   outputDir.createSync(recursive: true);
   final String vmSnapshotData = fs.path.join(outputDir.path, 'vm_snapshot_data');
   final String vmSnapshotInstructions = fs.path.join(outputDir.path, 'vm_snapshot_instr');
   final String isolateSnapshotData = fs.path.join(outputDir.path, 'isolate_snapshot_data');
   final String isolateSnapshotInstructions = fs.path.join(outputDir.path, 'isolate_snapshot_instr');
   final String dependencies = fs.path.join(outputDir.path, 'snapshot.d');
   final String assembly = fs.path.join(outputDir.path, 'snapshot_assembly.S');
   final String assemblyO = fs.path.join(outputDir.path, 'snapshot_assembly.o');
   final String assemblySo = fs.path.join(outputDir.path, 'app.so');
   final bool compileToSharedLibrary =
       preferSharedLibrary && androidSdk.ndkCompiler != null;

   if (preferSharedLibrary && !compileToSharedLibrary) {
     printStatus(
         'Could not find NDK compiler. Not building in shared library mode');
   }

   final String vmEntryPoints = artifacts.getArtifactPath(
     Artifact.dartVmEntryPointsTxt,
     platform,
     buildMode,
   );
   final String ioEntryPoints = artifacts.getArtifactPath(Artifact.dartIoEntriesTxt, platform, buildMode);

   final List<String> entryPointsJsonFiles = <String>[];
   if (previewDart2 && !interpreter) {
     entryPointsJsonFiles.addAll(<String>[
       artifacts.getArtifactPath(Artifact.entryPointsJson, platform, buildMode),
       artifacts.getArtifactPath(Artifact.entryPointsExtraJson, platform, buildMode),
     ]);
   }

   final PackageMap packageMap = new PackageMap(PackageMap.globalPackagesPath);
   final String packageMapError = packageMap.checkValid();
   if (packageMapError != null) {
     printError(packageMapError);
     return null;
   }

   final String skyEnginePkg = _getPackagePath(packageMap, 'sky_engine');
   final String uiPath = fs.path.join(skyEnginePkg, 'lib', 'ui', 'ui.dart');
   final String vmServicePath = fs.path.join(skyEnginePkg, 'sdk_ext', 'vmservice_io.dart');

   final List<String> inputPaths = <String>[
     vmEntryPoints,
     ioEntryPoints,
     uiPath,
     vmServicePath,
     mainPath,
   ];

   inputPaths.addAll(entryPointsJsonFiles);

   final Set<String> outputPaths = new Set<String>();

   // These paths are used only on iOS.
   String snapshotDartIOS;

   switch (platform) {
     case TargetPlatform.android_arm:
     case TargetPlatform.android_arm64:
     case TargetPlatform.android_x64:
     case TargetPlatform.android_x86:
       if (compileToSharedLibrary) {
         outputPaths.add(assemblySo);
       } else {
         outputPaths.addAll(<String>[
           vmSnapshotData,
           isolateSnapshotData,
         ]);
       }
       break;
     case TargetPlatform.ios:
       snapshotDartIOS = artifacts.getArtifactPath(Artifact.snapshotDart, platform, buildMode);
       inputPaths.add(snapshotDartIOS);
       break;
     case TargetPlatform.darwin_x64:
     case TargetPlatform.linux_x64:
     case TargetPlatform.windows_x64:
     case TargetPlatform.fuchsia:
     case TargetPlatform.tester:
       assert(false);
   }

   final Iterable<String> missingInputs = inputPaths.where((String p) => !fs.isFileSync(p));
   if (missingInputs.isNotEmpty) {
     printError('Missing input files: $missingInputs');
     return null;
   }

   final List<String> genSnapshotArgs = <String>[
     '--vm_snapshot_data=$vmSnapshotData',
     '--isolate_snapshot_data=$isolateSnapshotData',
     '--url_mapping=dart:ui,$uiPath',
     '--url_mapping=dart:vmservice_io,$vmServicePath',
     '--dependencies=$dependencies',
   ];

   if ((extraFrontEndOptions != null) && extraFrontEndOptions.isNotEmpty)
     printTrace('Extra front-end options: $extraFrontEndOptions');

   if ((extraGenSnapshotOptions != null) && extraGenSnapshotOptions.isNotEmpty) {
     printTrace('Extra gen-snapshot options: $extraGenSnapshotOptions');
     genSnapshotArgs.addAll(extraGenSnapshotOptions);
   }

   if (!interpreter) {
     genSnapshotArgs.add('--embedder_entry_points_manifest=$vmEntryPoints');
     genSnapshotArgs.add('--embedder_entry_points_manifest=$ioEntryPoints');
   }

   // iOS symbols used to load snapshot data in the engine.
   const String kVmSnapshotData = 'kDartVmSnapshotData';
   const String kIsolateSnapshotData = 'kDartIsolateSnapshotData';

   // iOS snapshot generated files, compiled object files.
   final String kVmSnapshotDataC = fs.path.join(outputDir.path, '$kVmSnapshotData.c');
   final String kIsolateSnapshotDataC = fs.path.join(outputDir.path, '$kIsolateSnapshotData.c');
   final String kVmSnapshotDataO = fs.path.join(outputDir.path, '$kVmSnapshotData.o');
   final String kIsolateSnapshotDataO = fs.path.join(outputDir.path, '$kIsolateSnapshotData.o');
   final String kApplicationKernelPath = fs.path.join(getBuildDirectory(), 'app.dill');

   switch (platform) {
     case TargetPlatform.android_arm:
     case TargetPlatform.android_arm64:
     case TargetPlatform.android_x64:
     case TargetPlatform.android_x86:
       if (compileToSharedLibrary) {
         genSnapshotArgs.add('--snapshot_kind=app-aot-assembly');
         genSnapshotArgs.add('--assembly=$assembly');
         outputPaths.add(assemblySo);
       } else {
         genSnapshotArgs.addAll(<String>[
           '--snapshot_kind=app-aot-blobs',
           '--vm_snapshot_instructions=$vmSnapshotInstructions',
           '--isolate_snapshot_instructions=$isolateSnapshotInstructions',
         ]);
       }
       if (platform == TargetPlatform.android_arm) {
         genSnapshotArgs.addAll(<String>[
           '--no-sim-use-hardfp', // Android uses the softfloat ABI.
           '--no-use-integer-division', // Not supported by the Pixel in 32-bit mode.
         ]);
       }
       break;
     case TargetPlatform.ios:
       if (interpreter) {
         genSnapshotArgs.add('--snapshot_kind=core');
         genSnapshotArgs.add(snapshotDartIOS);
         outputPaths.addAll(<String>[
           kVmSnapshotDataO,
           kIsolateSnapshotDataO,
         ]);
       } else {
         genSnapshotArgs.add('--snapshot_kind=app-aot-assembly');
         genSnapshotArgs.add('--assembly=$assembly');
         outputPaths.add(assemblyO);
       }
       break;
     case TargetPlatform.darwin_x64:
     case TargetPlatform.linux_x64:
     case TargetPlatform.windows_x64:
     case TargetPlatform.fuchsia:
     case TargetPlatform.tester:
       assert(false);
   }

   if (buildMode != BuildMode.release) {
     genSnapshotArgs.addAll(<String>[
       '--no-checked',
       '--conditional_directives',
     ]);
   }

   final String entryPoint = mainPath;
   final SnapshotType snapshotType = new SnapshotType(platform, buildMode);
   Future<Fingerprint> makeFingerprint() async {
     final Set<String> snapshotInputPaths = await readDepfile(dependencies)
       ..add(entryPoint)
       ..addAll(outputPaths);
     return Snapshotter.createFingerprint(snapshotType, entryPoint, snapshotInputPaths);
   }

   final File fingerprintFile = fs.file('$dependencies.fingerprint');
   final List<File> fingerprintFiles = <File>[fingerprintFile, fs.file(dependencies)]
     ..addAll(inputPaths.map(fs.file))
     ..addAll(outputPaths.map(fs.file));
   if (fingerprintFiles.every((File file) => file.existsSync())) {
     try {
       final String json = await fingerprintFile.readAsString();
       final Fingerprint oldFingerprint = new Fingerprint.fromJson(json);
       if (oldFingerprint == await makeFingerprint()) {
         printStatus('Skipping AOT snapshot build. Fingerprint match.');
         return outputPath;
       }
     } catch (e) {
       // Log exception and continue, this step is a performance improvement only.
       printTrace('Rebuilding snapshot due to fingerprint check error: $e');
     }
   }

   if (previewDart2) {
     final CompilerOutput compilerOutput = await kernelCompiler.compile(
       sdkRoot: artifacts.getArtifactPath(Artifact.flutterPatchedSdkPath),
       mainPath: mainPath,
       outputFilePath: kApplicationKernelPath,
       depFilePath: dependencies,
       extraFrontEndOptions: extraFrontEndOptions,
       linkPlatformKernelIn : true,
       aot : !interpreter,
       entryPointsJsonFiles: entryPointsJsonFiles,
       trackWidgetCreation: false,
     );
     mainPath = compilerOutput?.outputFilename;
     if (mainPath == null) {
       printError('Compiler terminated unexpectedly.');
       return null;
     }
     // Write path to frontend_server, since things need to be re-generated when
     // that changes.
     await outputDir.childFile('frontend_server.d')
         .writeAsString('frontend_server.d: ${artifacts.getArtifactPath(Artifact.frontendServerSnapshotForEngineDartSdk)}\n');

     genSnapshotArgs.addAll(<String>[
       '--reify-generic-functions',
       '--strong',
     ]);
   }

   genSnapshotArgs.add(mainPath);

   final int genSnapshotExitCode = await genSnapshot.run(
     snapshotType: new SnapshotType(platform, buildMode),
     packagesPath: packageMap.packagesPath,
     depfilePath: dependencies,
     additionalArgs: genSnapshotArgs,
   );
   if (genSnapshotExitCode != 0) {
     printError('Dart snapshot generator failed with exit code $genSnapshotExitCode');
     return null;
   }

   // Write path to gen_snapshot, since snapshots have to be re-generated when we roll
   // the Dart SDK.
   await outputDir.childFile('gen_snapshot.d').writeAsString('snapshot.d: $genSnapshot\n');

   // On iOS, we use Xcode to compile the snapshot into a dynamic library that the
   // end-developer can link into their app.
   if (platform == TargetPlatform.ios) {
     printStatus('Building App.framework...');

     final List<String> commonBuildOptions = <String>['-arch', 'arm64', '-miphoneos-version-min=8.0'];

     if (interpreter) {
       await runCheckedAsync(<String>['mv', vmSnapshotData, fs.path.join(outputDir.path, kVmSnapshotData)]);
       await runCheckedAsync(<String>['mv', isolateSnapshotData, fs.path.join(outputDir.path, kIsolateSnapshotData)]);

       await runCheckedAsync(<String>[
         'xxd', '--include', kVmSnapshotData, fs.path.basename(kVmSnapshotDataC)
       ], workingDirectory: outputDir.path);
       await runCheckedAsync(<String>[
         'xxd', '--include', kIsolateSnapshotData, fs.path.basename(kIsolateSnapshotDataC)
       ], workingDirectory: outputDir.path);

       await runCheckedAsync(<String>['xcrun', 'cc']
         ..addAll(commonBuildOptions)
         ..addAll(<String>['-c', kVmSnapshotDataC, '-o', kVmSnapshotDataO]));
       await runCheckedAsync(<String>['xcrun', 'cc']
         ..addAll(commonBuildOptions)
         ..addAll(<String>['-c', kIsolateSnapshotDataC, '-o', kIsolateSnapshotDataO]));
     } else {
       await runCheckedAsync(<String>['xcrun', 'cc']
         ..addAll(commonBuildOptions)
         ..addAll(<String>['-c', assembly, '-o', assemblyO]));
     }

     final String frameworkDir = fs.path.join(outputDir.path, 'App.framework');
     fs.directory(frameworkDir).createSync(recursive: true);
     final String appLib = fs.path.join(frameworkDir, 'App');
     final List<String> linkCommand = <String>['xcrun', 'clang']
       ..addAll(commonBuildOptions)
       ..addAll(<String>[
         '-dynamiclib',
         '-Xlinker', '-rpath', '-Xlinker', '@executable_path/Frameworks',
         '-Xlinker', '-rpath', '-Xlinker', '@loader_path/Frameworks',
         '-install_name', '@rpath/App.framework/App',
         '-o', appLib,
     ]);
     if (interpreter) {
       linkCommand.add(kVmSnapshotDataO);
       linkCommand.add(kIsolateSnapshotDataO);
     } else {
       linkCommand.add(assemblyO);
     }
     await runCheckedAsync(linkCommand);
   } else {
     if (compileToSharedLibrary) {
       // A word of warning: Instead of compiling via two steps, to a .o file and
       // then to a .so file we use only one command. When using two commands
       // gcc will end up putting a .eh_frame and a .debug_frame into the shared
       // library. Without stripping .debug_frame afterwards, unwinding tools
       // based upon libunwind use just one and ignore the contents of the other
       // (which causes it to not look into the other section and therefore not
       // find the correct unwinding information).
       await runCheckedAsync(<String>[androidSdk.ndkCompiler]
           ..addAll(androidSdk.ndkCompilerArgs)
           ..addAll(<String>[ '-shared', '-nostdlib', '-o', assemblySo, assembly ]));
     }
   }

   // Compute and record build fingerprint.
   try {
     final Fingerprint fingerprint = await makeFingerprint();
     await fingerprintFile.writeAsString(fingerprint.toJson());
   } catch (e, s) {
     // Log exception and continue, this step is a performance improvement only.
     printStatus('Error during AOT snapshot fingerprinting: $e\n$s');
   }

   return outputPath;
 }
	// Copyright 2016 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 '../android/android_sdk.dart';
	import '../artifacts.dart';
	import '../base/build.dart';
	import '../base/common.dart';
	import '../base/file_system.dart';
	import '../base/logger.dart';
	import '../base/process.dart';
	import '../base/utils.dart';
	import '../build_info.dart';
	import '../compile.dart';
	import '../dart/package_map.dart';
	import '../globals.dart';
	import '../resident_runner.dart';
	import '../runner/flutter_command.dart';
	import 'build.dart';

	// Files generated by the ahead-of-time snapshot builder.
	const List<String> kAotSnapshotFiles = const <String>[
	'vm_snapshot_data', 'vm_snapshot_instr', 'isolate_snapshot_data', 'isolate_snapshot_instr',
	];

	class BuildAotCommand extends BuildSubCommand {
	BuildAotCommand({bool verboseHelp: false}) {
	usesTargetOption();
	addBuildModeFlags();
	usesPubOption();
	argParser
	..addOption('output-dir', defaultsTo: getAotBuildDirectory())
	..addOption('target-platform',
	defaultsTo: 'android-arm',
	allowed: <String>['android-arm', 'android-arm64', 'ios']
	)
	..addFlag('interpreter')
	..addFlag('quiet', defaultsTo: false)
	..addFlag('preview-dart-2',
	defaultsTo: true,
	hide: !verboseHelp,
	help: 'Preview Dart 2.0 functionality.',
	)
	..addMultiOption(FlutterOptions.kExtraFrontEndOptions,
	splitCommas: true,
	hide: true,
	)
	..addMultiOption(FlutterOptions.kExtraGenSnapshotOptions,
	splitCommas: true,
	hide: true,
	)
	..addFlag('prefer-shared-library',
	negatable: false,
	help: 'Whether to prefer compiling to a *.so file (android only).');
	}

	@override
	final String name = 'aot';

	@override
	final String description = "Build an ahead-of-time compiled snapshot of your app's Dart code.";

	@override
	Future<Null> runCommand() async {
	await super.runCommand();
	final String targetPlatform = argResults['target-platform'];
	final TargetPlatform platform = getTargetPlatformForName(targetPlatform);
	if (platform == null)
	throwToolExit('Unknown platform: $targetPlatform');

	final String typeName = artifacts.getEngineType(platform, getBuildMode());
	Status status;
	if (!argResults['quiet']) {
	status = logger.startProgress('Building AOT snapshot in ${getModeName(getBuildMode())} mode ($typeName)...',
	expectSlowOperation: true);
	}
	final String outputPath = await buildAotSnapshot(
	findMainDartFile(targetFile),
	platform,
	getBuildMode(),
	outputPath: argResults['output-dir'],
	interpreter: argResults['interpreter'],
	previewDart2: argResults['preview-dart-2'],
	extraFrontEndOptions: argResults[FlutterOptions.kExtraFrontEndOptions],
	extraGenSnapshotOptions: argResults[FlutterOptions.kExtraGenSnapshotOptions],
	preferSharedLibrary: argResults['prefer-shared-library'],
	);
	status?.stop();

	if (outputPath == null)
	throwToolExit(null);

	final String builtMessage = 'Built to $outputPath${fs.path.separator}.';
	if (argResults['quiet']) {
	printTrace(builtMessage);
	} else {
	printStatus(builtMessage);
	}
	}
	}

	String _getPackagePath(PackageMap packageMap, String package) {
	return fs.path.dirname(packageMap.map[package].toFilePath());
	}

	/// Build an AOT snapshot. Return null (and log to `printError`) if the method
	/// fails.
	Future<String> buildAotSnapshot(
	String mainPath,
	TargetPlatform platform,
	BuildMode buildMode, {
	String outputPath,
	bool interpreter: false,
	bool previewDart2: false,
	List<String> extraFrontEndOptions,
	List<String> extraGenSnapshotOptions,
	bool preferSharedLibrary: false,
	}) async {
	outputPath ??= getAotBuildDirectory();
	try {
	return _buildAotSnapshot(
	mainPath,
	platform,
	buildMode,
	outputPath: outputPath,
	interpreter: interpreter,
	previewDart2: previewDart2,
	extraFrontEndOptions: extraFrontEndOptions,
	extraGenSnapshotOptions: extraGenSnapshotOptions,
	preferSharedLibrary: preferSharedLibrary,
	);
	} on String catch (error) {
	// Catch the String exceptions thrown from the `runCheckedSync` methods below.
	printError(error);
	return null;
	}
	}

	// TODO(cbracken): split AOT and Assembly AOT snapshotting logic and migrate to Snapshotter class.
	Future<String> _buildAotSnapshot(
	String mainPath,
	TargetPlatform platform,
	BuildMode buildMode, {
	String outputPath,
	bool interpreter: false,
	bool previewDart2: false,
	List<String> extraFrontEndOptions,
	List<String> extraGenSnapshotOptions,
	bool preferSharedLibrary: false,
	}) async {
	outputPath ??= getAotBuildDirectory();
	if (!isAotBuildMode(buildMode) && !interpreter) {
	printError('${toTitleCase(getModeName(buildMode))} mode does not support AOT compilation.');
	return null;
	}

	if (!(platform == TargetPlatform.android_arm \|\|
	platform == TargetPlatform.android_arm64 \|\|
	platform == TargetPlatform.ios)) {
	printError('${getNameForTargetPlatform(platform)} does not support AOT compilation.');
	return null;
	}

	final Directory outputDir = fs.directory(outputPath);
	outputDir.createSync(recursive: true);
	final String vmSnapshotData = fs.path.join(outputDir.path, 'vm_snapshot_data');
	final String vmSnapshotInstructions = fs.path.join(outputDir.path, 'vm_snapshot_instr');
	final String isolateSnapshotData = fs.path.join(outputDir.path, 'isolate_snapshot_data');
	final String isolateSnapshotInstructions = fs.path.join(outputDir.path, 'isolate_snapshot_instr');
	final String dependencies = fs.path.join(outputDir.path, 'snapshot.d');
	final String assembly = fs.path.join(outputDir.path, 'snapshot_assembly.S');
	final String assemblyO = fs.path.join(outputDir.path, 'snapshot_assembly.o');
	final String assemblySo = fs.path.join(outputDir.path, 'app.so');
	final bool compileToSharedLibrary =
	preferSharedLibrary && androidSdk.ndkCompiler != null;

	if (preferSharedLibrary && !compileToSharedLibrary) {
	printStatus(
	'Could not find NDK compiler. Not building in shared library mode');
	}

	final String vmEntryPoints = artifacts.getArtifactPath(
	Artifact.dartVmEntryPointsTxt,
	platform,
	buildMode,
	);
	final String ioEntryPoints = artifacts.getArtifactPath(Artifact.dartIoEntriesTxt, platform, buildMode);

	final List<String> entryPointsJsonFiles = <String>[];
	if (previewDart2 && !interpreter) {
	entryPointsJsonFiles.addAll(<String>[
	artifacts.getArtifactPath(Artifact.entryPointsJson, platform, buildMode),
	artifacts.getArtifactPath(Artifact.entryPointsExtraJson, platform, buildMode),
	]);
	}

	final PackageMap packageMap = new PackageMap(PackageMap.globalPackagesPath);
	final String packageMapError = packageMap.checkValid();
	if (packageMapError != null) {
	printError(packageMapError);
	return null;
	}

	final String skyEnginePkg = _getPackagePath(packageMap, 'sky_engine');
	final String uiPath = fs.path.join(skyEnginePkg, 'lib', 'ui', 'ui.dart');
	final String vmServicePath = fs.path.join(skyEnginePkg, 'sdk_ext', 'vmservice_io.dart');

	final List<String> inputPaths = <String>[
	vmEntryPoints,
	ioEntryPoints,
	uiPath,
	vmServicePath,
	mainPath,
	];

	inputPaths.addAll(entryPointsJsonFiles);

	final Set<String> outputPaths = new Set<String>();

	// These paths are used only on iOS.
	String snapshotDartIOS;

	switch (platform) {
	case TargetPlatform.android_arm:
	case TargetPlatform.android_arm64:
	case TargetPlatform.android_x64:
	case TargetPlatform.android_x86:
	if (compileToSharedLibrary) {
	outputPaths.add(assemblySo);
	} else {
	outputPaths.addAll(<String>[
	vmSnapshotData,
	isolateSnapshotData,
	]);
	}
	break;
	case TargetPlatform.ios:
	snapshotDartIOS = artifacts.getArtifactPath(Artifact.snapshotDart, platform, buildMode);
	inputPaths.add(snapshotDartIOS);
	break;
	case TargetPlatform.darwin_x64:
	case TargetPlatform.linux_x64:
	case TargetPlatform.windows_x64:
	case TargetPlatform.fuchsia:
	case TargetPlatform.tester:
	assert(false);
	}

	final Iterable<String> missingInputs = inputPaths.where((String p) => !fs.isFileSync(p));
	if (missingInputs.isNotEmpty) {
	printError('Missing input files: $missingInputs');
	return null;
	}

	final List<String> genSnapshotArgs = <String>[
	'--vm_snapshot_data=$vmSnapshotData',
	'--isolate_snapshot_data=$isolateSnapshotData',
	'--url_mapping=dart:ui,$uiPath',
	'--url_mapping=dart:vmservice_io,$vmServicePath',
	'--dependencies=$dependencies',
	];

	if ((extraFrontEndOptions != null) && extraFrontEndOptions.isNotEmpty)
	printTrace('Extra front-end options: $extraFrontEndOptions');

	if ((extraGenSnapshotOptions != null) && extraGenSnapshotOptions.isNotEmpty) {
	printTrace('Extra gen-snapshot options: $extraGenSnapshotOptions');
	genSnapshotArgs.addAll(extraGenSnapshotOptions);
	}

	if (!interpreter) {
	genSnapshotArgs.add('--embedder_entry_points_manifest=$vmEntryPoints');
	genSnapshotArgs.add('--embedder_entry_points_manifest=$ioEntryPoints');
	}

	// iOS symbols used to load snapshot data in the engine.
	const String kVmSnapshotData = 'kDartVmSnapshotData';
	const String kIsolateSnapshotData = 'kDartIsolateSnapshotData';

	// iOS snapshot generated files, compiled object files.
	final String kVmSnapshotDataC = fs.path.join(outputDir.path, '$kVmSnapshotData.c');
	final String kIsolateSnapshotDataC = fs.path.join(outputDir.path, '$kIsolateSnapshotData.c');
	final String kVmSnapshotDataO = fs.path.join(outputDir.path, '$kVmSnapshotData.o');
	final String kIsolateSnapshotDataO = fs.path.join(outputDir.path, '$kIsolateSnapshotData.o');
	final String kApplicationKernelPath = fs.path.join(getBuildDirectory(), 'app.dill');

	switch (platform) {
	case TargetPlatform.android_arm:
	case TargetPlatform.android_arm64:
	case TargetPlatform.android_x64:
	case TargetPlatform.android_x86:
	if (compileToSharedLibrary) {
	genSnapshotArgs.add('--snapshot_kind=app-aot-assembly');
	genSnapshotArgs.add('--assembly=$assembly');
	outputPaths.add(assemblySo);
	} else {
	genSnapshotArgs.addAll(<String>[
	'--snapshot_kind=app-aot-blobs',
	'--vm_snapshot_instructions=$vmSnapshotInstructions',
	'--isolate_snapshot_instructions=$isolateSnapshotInstructions',
	]);
	}
	if (platform == TargetPlatform.android_arm) {
	genSnapshotArgs.addAll(<String>[
	'--no-sim-use-hardfp', // Android uses the softfloat ABI.
	'--no-use-integer-division', // Not supported by the Pixel in 32-bit mode.
	]);
	}
	break;
	case TargetPlatform.ios:
	if (interpreter) {
	genSnapshotArgs.add('--snapshot_kind=core');
	genSnapshotArgs.add(snapshotDartIOS);
	outputPaths.addAll(<String>[
	kVmSnapshotDataO,
	kIsolateSnapshotDataO,
	]);
	} else {
	genSnapshotArgs.add('--snapshot_kind=app-aot-assembly');
	genSnapshotArgs.add('--assembly=$assembly');
	outputPaths.add(assemblyO);
	}
	break;
	case TargetPlatform.darwin_x64:
	case TargetPlatform.linux_x64:
	case TargetPlatform.windows_x64:
	case TargetPlatform.fuchsia:
	case TargetPlatform.tester:
	assert(false);
	}

	if (buildMode != BuildMode.release) {
	genSnapshotArgs.addAll(<String>[
	'--no-checked',
	'--conditional_directives',
	]);
	}

	final String entryPoint = mainPath;
	final SnapshotType snapshotType = new SnapshotType(platform, buildMode);
	Future<Fingerprint> makeFingerprint() async {
	final Set<String> snapshotInputPaths = await readDepfile(dependencies)
	..add(entryPoint)
	..addAll(outputPaths);
	return Snapshotter.createFingerprint(snapshotType, entryPoint, snapshotInputPaths);
	}

	final File fingerprintFile = fs.file('$dependencies.fingerprint');
	final List<File> fingerprintFiles = <File>[fingerprintFile, fs.file(dependencies)]
	..addAll(inputPaths.map(fs.file))
	..addAll(outputPaths.map(fs.file));
	if (fingerprintFiles.every((File file) => file.existsSync())) {
	try {
	final String json = await fingerprintFile.readAsString();
	final Fingerprint oldFingerprint = new Fingerprint.fromJson(json);
	if (oldFingerprint == await makeFingerprint()) {
	printStatus('Skipping AOT snapshot build. Fingerprint match.');
	return outputPath;
	}
	} catch (e) {
	// Log exception and continue, this step is a performance improvement only.
	printTrace('Rebuilding snapshot due to fingerprint check error: $e');
	}
	}

	if (previewDart2) {
	final CompilerOutput compilerOutput = await kernelCompiler.compile(
	sdkRoot: artifacts.getArtifactPath(Artifact.flutterPatchedSdkPath),
	mainPath: mainPath,
	outputFilePath: kApplicationKernelPath,
	depFilePath: dependencies,
	extraFrontEndOptions: extraFrontEndOptions,
	linkPlatformKernelIn : true,
	aot : !interpreter,
	entryPointsJsonFiles: entryPointsJsonFiles,
	trackWidgetCreation: false,
	);
	mainPath = compilerOutput?.outputFilename;
	if (mainPath == null) {
	printError('Compiler terminated unexpectedly.');
	return null;
	}
	// Write path to frontend_server, since things need to be re-generated when
	// that changes.
	await outputDir.childFile('frontend_server.d')
	.writeAsString('frontend_server.d: ${artifacts.getArtifactPath(Artifact.frontendServerSnapshotForEngineDartSdk)}\n');

	genSnapshotArgs.addAll(<String>[
	'--reify-generic-functions',
	'--strong',
	]);
	}

	genSnapshotArgs.add(mainPath);

	final int genSnapshotExitCode = await genSnapshot.run(
	snapshotType: new SnapshotType(platform, buildMode),
	packagesPath: packageMap.packagesPath,
	depfilePath: dependencies,
	additionalArgs: genSnapshotArgs,
	);
	if (genSnapshotExitCode != 0) {
	printError('Dart snapshot generator failed with exit code $genSnapshotExitCode');
	return null;
	}

	// Write path to gen_snapshot, since snapshots have to be re-generated when we roll
	// the Dart SDK.
	await outputDir.childFile('gen_snapshot.d').writeAsString('snapshot.d: $genSnapshot\n');

	// On iOS, we use Xcode to compile the snapshot into a dynamic library that the
	// end-developer can link into their app.
	if (platform == TargetPlatform.ios) {
	printStatus('Building App.framework...');

	final List<String> commonBuildOptions = <String>['-arch', 'arm64', '-miphoneos-version-min=8.0'];

	if (interpreter) {
	await runCheckedAsync(<String>['mv', vmSnapshotData, fs.path.join(outputDir.path, kVmSnapshotData)]);
	await runCheckedAsync(<String>['mv', isolateSnapshotData, fs.path.join(outputDir.path, kIsolateSnapshotData)]);

	await runCheckedAsync(<String>[
	'xxd', '--include', kVmSnapshotData, fs.path.basename(kVmSnapshotDataC)
	], workingDirectory: outputDir.path);
	await runCheckedAsync(<String>[
	'xxd', '--include', kIsolateSnapshotData, fs.path.basename(kIsolateSnapshotDataC)
	], workingDirectory: outputDir.path);

	await runCheckedAsync(<String>['xcrun', 'cc']
	..addAll(commonBuildOptions)
	..addAll(<String>['-c', kVmSnapshotDataC, '-o', kVmSnapshotDataO]));
	await runCheckedAsync(<String>['xcrun', 'cc']
	..addAll(commonBuildOptions)
	..addAll(<String>['-c', kIsolateSnapshotDataC, '-o', kIsolateSnapshotDataO]));
	} else {
	await runCheckedAsync(<String>['xcrun', 'cc']
	..addAll(commonBuildOptions)
	..addAll(<String>['-c', assembly, '-o', assemblyO]));
	}

	final String frameworkDir = fs.path.join(outputDir.path, 'App.framework');
	fs.directory(frameworkDir).createSync(recursive: true);
	final String appLib = fs.path.join(frameworkDir, 'App');
	final List<String> linkCommand = <String>['xcrun', 'clang']
	..addAll(commonBuildOptions)
	..addAll(<String>[
	'-dynamiclib',
	'-Xlinker', '-rpath', '-Xlinker', '@executable_path/Frameworks',
	'-Xlinker', '-rpath', '-Xlinker', '@loader_path/Frameworks',
	'-install_name', '@rpath/App.framework/App',
	'-o', appLib,
	]);
	if (interpreter) {
	linkCommand.add(kVmSnapshotDataO);
	linkCommand.add(kIsolateSnapshotDataO);
	} else {
	linkCommand.add(assemblyO);
	}
	await runCheckedAsync(linkCommand);
	} else {
	if (compileToSharedLibrary) {
	// A word of warning: Instead of compiling via two steps, to a .o file and
	// then to a .so file we use only one command. When using two commands
	// gcc will end up putting a .eh_frame and a .debug_frame into the shared
	// library. Without stripping .debug_frame afterwards, unwinding tools
	// based upon libunwind use just one and ignore the contents of the other
	// (which causes it to not look into the other section and therefore not
	// find the correct unwinding information).
	await runCheckedAsync(<String>[androidSdk.ndkCompiler]
	..addAll(androidSdk.ndkCompilerArgs)
	..addAll(<String>[ '-shared', '-nostdlib', '-o', assemblySo, assembly ]));
	}
	}

	// Compute and record build fingerprint.
	try {
	final Fingerprint fingerprint = await makeFingerprint();
	await fingerprintFile.writeAsString(fingerprint.toJson());
	} catch (e, s) {
	// Log exception and continue, this step is a performance improvement only.
	printStatus('Error during AOT snapshot fingerprinting: $e\n$s');
	}

	return outputPath;
	}