[flutter_tool] Remove some async file io (#38654)

diff --git a/packages/flutter_tools/lib/runner.dart b/packages/flutter_tools/lib/runner.dart
index 6999486..0734f13 100644
--- a/packages/flutter_tools/lib/runner.dart
+++ b/packages/flutter_tools/lib/runner.dart

@@ -179,12 +179,12 @@
   buffer.writeln('```\n${await _doctorText()}```');
 
   try {
-    await crashFile.writeAsString(buffer.toString());
+    crashFile.writeAsStringSync(buffer.toString());
   } on FileSystemException catch (_) {
     // Fallback to the system temporary directory.
     crashFile = getUniqueFile(crashFileSystem.systemTempDirectory, 'flutter', 'log');
     try {
-      await crashFile.writeAsString(buffer.toString());
+      crashFile.writeAsStringSync(buffer.toString());
     } on FileSystemException catch (e) {
       printError('Could not write crash report to disk: $e');
       printError(buffer.toString());

diff --git a/packages/flutter_tools/lib/src/asset.dart b/packages/flutter_tools/lib/src/asset.dart
index d121d83..737c9c7 100644
--- a/packages/flutter_tools/lib/src/asset.dart
+++ b/packages/flutter_tools/lib/src/asset.dart

@@ -235,7 +235,7 @@
     entries[_fontManifestJson] = DevFSStringContent(json.encode(fonts));
 
     // TODO(ianh): Only do the following line if we've changed packages or if our LICENSE file changed
-    entries[_license] = await _obtainLicenses(packageMap, assetBasePath, reportPackages: reportLicensedPackages);
+    entries[_license] = _obtainLicenses(packageMap, assetBasePath, reportPackages: reportLicensedPackages);
 
     return 0;
   }
@@ -325,11 +325,11 @@
 final String _licenseSeparator = '\n' + ('-' * 80) + '\n';
 
 /// Returns a DevFSContent representing the license file.
-Future<DevFSContent> _obtainLicenses(
+DevFSContent _obtainLicenses(
   PackageMap packageMap,
   String assetBase, {
   bool reportPackages,
-}) async {
+}) {
   // Read the LICENSE file from each package in the .packages file, splitting
   // each one into each component license (so that we can de-dupe if possible).
   //
@@ -347,30 +347,32 @@
   final Set<String> allPackages = <String>{};
   for (String packageName in packageMap.map.keys) {
     final Uri package = packageMap.map[packageName];
-    if (package != null && package.scheme == 'file') {
-      final File file = fs.file(package.resolve('../LICENSE'));
-      if (file.existsSync()) {
-        final List<String> rawLicenses =
-            (await file.readAsString()).split(_licenseSeparator);
-        for (String rawLicense in rawLicenses) {
-          List<String> packageNames;
-          String licenseText;
-          if (rawLicenses.length > 1) {
-            final int split = rawLicense.indexOf('\n\n');
-            if (split >= 0) {
-              packageNames = rawLicense.substring(0, split).split('\n');
-              licenseText = rawLicense.substring(split + 2);
-            }
-          }
-          if (licenseText == null) {
-            packageNames = <String>[packageName];
-            licenseText = rawLicense;
-          }
-          packageLicenses.putIfAbsent(licenseText, () => <String>{})
-            ..addAll(packageNames);
-          allPackages.addAll(packageNames);
+    if (package == null || package.scheme != 'file') {
+      continue;
+    }
+    final File file = fs.file(package.resolve('../LICENSE'));
+    if (!file.existsSync()) {
+      continue;
+    }
+    final List<String> rawLicenses =
+        file.readAsStringSync().split(_licenseSeparator);
+    for (String rawLicense in rawLicenses) {
+      List<String> packageNames;
+      String licenseText;
+      if (rawLicenses.length > 1) {
+        final int split = rawLicense.indexOf('\n\n');
+        if (split >= 0) {
+          packageNames = rawLicense.substring(0, split).split('\n');
+          licenseText = rawLicense.substring(split + 2);
         }
       }
+      if (licenseText == null) {
+        packageNames = <String>[packageName];
+        licenseText = rawLicense;
+      }
+      packageLicenses.putIfAbsent(licenseText, () => <String>{})
+        ..addAll(packageNames);
+      allPackages.addAll(packageNames);
     }
   }
 

diff --git a/packages/flutter_tools/lib/src/base/build.dart b/packages/flutter_tools/lib/src/base/build.dart
index 51bcbcc..695d869 100644
--- a/packages/flutter_tools/lib/src/base/build.dart
+++ b/packages/flutter_tools/lib/src/base/build.dart

@@ -180,7 +180,7 @@
     // gen_snapshot would provide an argument to do this automatically.
     if (platform == TargetPlatform.ios && bitcode) {
       final IOSink sink = fs.file('$assembly.bitcode').openWrite();
-      for (String line in await fs.file(assembly).readAsLines()) {
+      for (String line in fs.file(assembly).readAsLinesSync()) {
         if (line.startsWith('.section __DWARF')) {
           break;
         }
@@ -192,7 +192,7 @@
     // Write path to gen_snapshot, since snapshots have to be re-generated when we roll
     // the Dart SDK.
     final String genSnapshotPath = GenSnapshot.getSnapshotterPath(snapshotType);
-    await outputDir.childFile('gen_snapshot.d').writeAsString('gen_snapshot.d: $genSnapshotPath\n');
+    outputDir.childFile('gen_snapshot.d').writeAsStringSync('gen_snapshot.d: $genSnapshotPath\n');
 
     // On iOS, we use Xcode to compile the snapshot into a dynamic library that the
     // end-developer can link into their app.
@@ -313,7 +313,7 @@
 
     // Write path to frontend_server, since things need to be re-generated when that changes.
     final String frontendPath = artifacts.getArtifactPath(Artifact.frontendServerSnapshotForEngineDartSdk);
-    await fs.directory(outputPath).childFile('frontend_server.d').writeAsString('frontend_server.d: $frontendPath\n');
+    fs.directory(outputPath).childFile('frontend_server.d').writeAsStringSync('frontend_server.d: $frontendPath\n');
 
     return compilerOutput?.outputFilename;
   }

diff --git a/packages/flutter_tools/lib/src/base/fingerprint.dart b/packages/flutter_tools/lib/src/base/fingerprint.dart
index 69ce8fc..663a254 100644
--- a/packages/flutter_tools/lib/src/base/fingerprint.dart
+++ b/packages/flutter_tools/lib/src/base/fingerprint.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:crypto/crypto.dart' show md5;
 import 'package:meta/meta.dart';
 import 'package:quiver/core.dart' show hash2;
@@ -52,12 +50,12 @@
   final List<String> _depfilePaths;
   final FingerprintPathFilter _pathFilter;
 
-  Future<Fingerprint> buildFingerprint() async {
-    final List<String> paths = await _getPaths();
+  Fingerprint buildFingerprint() {
+    final List<String> paths = _getPaths();
     return Fingerprint.fromBuildInputs(_properties, paths);
   }
 
-  Future<bool> doesFingerprintMatch() async {
+  bool doesFingerprintMatch() {
     if (_disableBuildCache) {
       return false;
     }
@@ -69,12 +67,12 @@
       if (!_depfilePaths.every(fs.isFileSync))
         return false;
 
-      final List<String> paths = await _getPaths();
+      final List<String> paths = _getPaths();
       if (!paths.every(fs.isFileSync))
         return false;
 
-      final Fingerprint oldFingerprint = Fingerprint.fromJson(await fingerprintFile.readAsString());
-      final Fingerprint newFingerprint = await buildFingerprint();
+      final Fingerprint oldFingerprint = Fingerprint.fromJson(fingerprintFile.readAsStringSync());
+      final Fingerprint newFingerprint = buildFingerprint();
       return oldFingerprint == newFingerprint;
     } catch (e) {
       // Log exception and continue, fingerprinting is only a performance improvement.
@@ -83,9 +81,9 @@
     return false;
   }
 
-  Future<void> writeFingerprint() async {
+  void writeFingerprint() {
     try {
-      final Fingerprint fingerprint = await buildFingerprint();
+      final Fingerprint fingerprint = buildFingerprint();
       fs.file(fingerprintPath).writeAsStringSync(fingerprint.toJson());
     } catch (e) {
       // Log exception and continue, fingerprinting is only a performance improvement.
@@ -93,11 +91,11 @@
     }
   }
 
-  Future<List<String>> _getPaths() async {
+  List<String> _getPaths() {
     final Set<String> paths = <String>{
       ..._paths,
       for (String depfilePath in _depfilePaths)
-        ...await readDepfile(depfilePath),
+        ...readDepfile(depfilePath),
     };
     final FingerprintPathFilter filter = _pathFilter ?? (String path) => true;
     return paths.where(filter).toList()..sort();
@@ -183,10 +181,10 @@
 /// outfile : file1.dart fil\\e2.dart fil\ e3.dart
 ///
 /// will return a set containing: 'file1.dart', 'fil\e2.dart', 'fil e3.dart'.
-Future<Set<String>> readDepfile(String depfilePath) async {
+Set<String> readDepfile(String depfilePath) {
   // Depfile format:
   // outfile1 outfile2 : file1.dart file2.dart file3.dart
-  final String contents = await fs.file(depfilePath).readAsString();
+  final String contents = fs.file(depfilePath).readAsStringSync();
 
   final String dependencies = contents.split(': ')[1];
   return dependencies

diff --git a/packages/flutter_tools/lib/src/base/platform.dart b/packages/flutter_tools/lib/src/base/platform.dart
index 9ab824d..24d8a55 100644
--- a/packages/flutter_tools/lib/src/base/platform.dart
+++ b/packages/flutter_tools/lib/src/base/platform.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:platform/platform.dart';
 
 import 'context.dart';
@@ -25,17 +23,17 @@
 /// subdirectory.
 ///
 /// Returns the existing platform.
-Future<Platform> getRecordingPlatform(String location) async {
+Platform getRecordingPlatform(String location) {
   final Directory dir = getRecordingSink(location, _kRecordingType);
   final File file = _getPlatformManifest(dir);
-  await file.writeAsString(platform.toJson(), flush: true);
+  file.writeAsStringSync(platform.toJson(), flush: true);
   return platform;
 }
 
-Future<FakePlatform> getReplayPlatform(String location) async {
+FakePlatform getReplayPlatform(String location) {
   final Directory dir = getReplaySource(location, _kRecordingType);
   final File file = _getPlatformManifest(dir);
-  final String json = await file.readAsString();
+  final String json = file.readAsStringSync();
   return FakePlatform.fromJson(json);
 }
 

diff --git a/packages/flutter_tools/lib/src/base/process.dart b/packages/flutter_tools/lib/src/base/process.dart
index 1dd5765..f94384e 100644
--- a/packages/flutter_tools/lib/src/base/process.dart
+++ b/packages/flutter_tools/lib/src/base/process.dart

@@ -15,7 +15,7 @@
 typedef StringConverter = String Function(String string);
 
 /// A function that will be run before the VM exits.
-typedef ShutdownHook = Future<dynamic> Function();
+typedef ShutdownHook = FutureOr<dynamic> Function();
 
 // TODO(ianh): We have way too many ways to run subprocesses in this project.
 // Convert most of these into one or more lightweight wrappers around the
@@ -83,8 +83,12 @@
       printTrace('Shutdown hook priority ${stage.priority}');
       final List<ShutdownHook> hooks = _shutdownHooks.remove(stage);
       final List<Future<dynamic>> futures = <Future<dynamic>>[];
-      for (ShutdownHook shutdownHook in hooks)
-        futures.add(shutdownHook());
+      for (ShutdownHook shutdownHook in hooks) {
+        final FutureOr<dynamic> result = shutdownHook();
+        if (result is Future<dynamic>) {
+          futures.add(result);
+        }
+      }
       await Future.wait<dynamic>(futures);
     }
   } finally {

diff --git a/packages/flutter_tools/lib/src/build_runner/build_runner.dart b/packages/flutter_tools/lib/src/build_runner/build_runner.dart
index 6265c02..a550c8f 100644
--- a/packages/flutter_tools/lib/src/build_runner/build_runner.dart
+++ b/packages/flutter_tools/lib/src/build_runner/build_runner.dart

@@ -102,7 +102,7 @@
       }
       stringBuffer.writeln('  build_runner: ^$kMinimumBuildRunnerVersion');
       stringBuffer.writeln('  build_daemon: $kSupportedBuildDaemonVersion');
-      await syntheticPubspec.writeAsString(stringBuffer.toString());
+      syntheticPubspec.writeAsStringSync(stringBuffer.toString());
 
       await pubGet(
         context: PubContext.pubGet,

diff --git a/packages/flutter_tools/lib/src/build_runner/build_script.dart b/packages/flutter_tools/lib/src/build_runner/build_script.dart
index 4a1a284..728a1f3 100644
--- a/packages/flutter_tools/lib/src/build_runner/build_script.dart
+++ b/packages/flutter_tools/lib/src/build_runner/build_script.dart

@@ -376,7 +376,7 @@
   final Iterable<AssetId> allSrcs = allDeps.expand((Module module) => module.sources);
   await scratchSpace.ensureAssets(allSrcs, buildStep);
 
-  final String packageFile = await _createPackageFile(allSrcs, buildStep, scratchSpace);
+  final String packageFile = _createPackageFile(allSrcs, buildStep, scratchSpace);
   final String dartPath = dartEntrypointId.path.startsWith('lib/')
       ? 'package:${dartEntrypointId.package}/'
           '${dartEntrypointId.path.substring('lib/'.length)}'
@@ -430,7 +430,7 @@
 /// The filename is based off the MD5 hash of the asset path so that files are
 /// unique regarless of situations like `web/foo/bar.dart` vs
 /// `web/foo-bar.dart`.
-Future<String> _createPackageFile(Iterable<AssetId> inputSources, BuildStep buildStep, ScratchSpace scratchSpace) async {
+String _createPackageFile(Iterable<AssetId> inputSources, BuildStep buildStep, ScratchSpace scratchSpace) {
   final Uri inputUri = buildStep.inputId.uri;
   final String packageFileName =
       '.package-${md5.convert(inputUri.toString().codeUnits)}';
@@ -439,8 +439,7 @@
   final Set<String> packageNames = inputSources.map((AssetId s) => s.package).toSet();
   final String packagesFileContent =
       packageNames.map((String name) => '$name:packages/$name/').join('\n');
-  await packagesFile
-      .writeAsString('# Generated for $inputUri\n$packagesFileContent');
+  packagesFile .writeAsStringSync('# Generated for $inputUri\n$packagesFileContent');
   return packageFileName;
 }
 

diff --git a/packages/flutter_tools/lib/src/build_runner/build_script_generator.dart b/packages/flutter_tools/lib/src/build_runner/build_script_generator.dart
index ff010dd..8b59f9b 100644
--- a/packages/flutter_tools/lib/src/build_runner/build_script_generator.dart
+++ b/packages/flutter_tools/lib/src/build_runner/build_script_generator.dart

@@ -49,8 +49,8 @@
         // ignore_for_file: directives_ordering
         ${library.accept(emitter)}''');
       final File output = fs.file(location);
-      await output.create(recursive: true);
-      await fs.file(location).writeAsString(result);
+      output.createSync(recursive: true);
+      fs.file(location).writeAsStringSync(result);
     } on FormatterException {
       throwToolExit('Generated build script could not be parsed. '
         'This is likely caused by a misconfigured builder definition.');

diff --git a/packages/flutter_tools/lib/src/bundle.dart b/packages/flutter_tools/lib/src/bundle.dart
index f298114..573f985 100644
--- a/packages/flutter_tools/lib/src/bundle.dart
+++ b/packages/flutter_tools/lib/src/bundle.dart

@@ -99,8 +99,8 @@
       }
       kernelContent = DevFSFileContent(fs.file(compilerOutput.outputFilename));
 
-      await fs.directory(getBuildDirectory()).childFile('frontend_server.d')
-          .writeAsString('frontend_server.d: ${artifacts.getArtifactPath(Artifact.frontendServerSnapshotForEngineDartSdk)}\n');
+      fs.directory(getBuildDirectory()).childFile('frontend_server.d')
+          .writeAsStringSync('frontend_server.d: ${artifacts.getArtifactPath(Artifact.frontendServerSnapshotForEngineDartSdk)}\n');
     }
 
     final AssetBundle assets = await buildAssets(

diff --git a/packages/flutter_tools/lib/src/commands/create.dart b/packages/flutter_tools/lib/src/commands/create.dart
index fa8a198..c29458a 100644
--- a/packages/flutter_tools/lib/src/commands/create.dart
+++ b/packages/flutter_tools/lib/src/commands/create.dart

@@ -407,7 +407,7 @@
         break;
     }
     if (sampleCode != null) {
-      generatedFileCount += await _applySample(relativeDir, sampleCode);
+      generatedFileCount += _applySample(relativeDir, sampleCode);
     }
     printStatus('Wrote $generatedFileCount files.');
     printStatus('\nAll done!');
@@ -566,13 +566,13 @@
   // documentation website in sampleCode.  Returns the difference in the number
   // of files after applying the sample, since it also deletes the application's
   // test directory (since the template's test doesn't apply to the sample).
-  Future<int> _applySample(Directory directory, String sampleCode) async {
+  int _applySample(Directory directory, String sampleCode) {
     final File mainDartFile = directory.childDirectory('lib').childFile('main.dart');
-    await mainDartFile.create(recursive: true);
-    await mainDartFile.writeAsString(sampleCode);
+    mainDartFile.createSync(recursive: true);
+    mainDartFile.writeAsStringSync(sampleCode);
     final Directory testDir = directory.childDirectory('test');
     final List<FileSystemEntity> files = testDir.listSync(recursive: true);
-    await testDir.delete(recursive: true);
+    testDir.deleteSync(recursive: true);
     return -files.length;
   }
 

diff --git a/packages/flutter_tools/lib/src/commands/packages.dart b/packages/flutter_tools/lib/src/commands/packages.dart
index 6078a17..510e9bf 100644
--- a/packages/flutter_tools/lib/src/commands/packages.dart
+++ b/packages/flutter_tools/lib/src/commands/packages.dart

@@ -79,9 +79,9 @@
       return usageValues;
     }
     final FlutterProject rootProject = FlutterProject.fromPath(target);
-    final bool hasPlugins = await rootProject.flutterPluginsFile.exists();
+    final bool hasPlugins = rootProject.flutterPluginsFile.existsSync();
     if (hasPlugins) {
-      final int numberOfPlugins = (await rootProject.flutterPluginsFile.readAsLines()).length;
+      final int numberOfPlugins = (rootProject.flutterPluginsFile.readAsLinesSync()).length;
       usageValues[CustomDimensions.commandPackagesNumberPlugins] = '$numberOfPlugins';
     } else {
       usageValues[CustomDimensions.commandPackagesNumberPlugins] = '0';

diff --git a/packages/flutter_tools/lib/src/commands/screenshot.dart b/packages/flutter_tools/lib/src/commands/screenshot.dart
index e98f6ed..bda6f33 100644
--- a/packages/flutter_tools/lib/src/commands/screenshot.dart
+++ b/packages/flutter_tools/lib/src/commands/screenshot.dart

@@ -106,7 +106,7 @@
     } catch (error) {
       throwToolExit('Error taking screenshot: $error');
     }
-    await showOutputFileInfo(outputFile);
+    _showOutputFileInfo(outputFile);
   }
 
   Future<void> runSkia(File outputFile) async {
@@ -115,8 +115,8 @@
     final IOSink sink = outputFile.openWrite();
     sink.add(base64.decode(skp['skp']));
     await sink.close();
-    await showOutputFileInfo(outputFile);
-    await _ensureOutputIsNotJsonRpcError(outputFile);
+    _showOutputFileInfo(outputFile);
+    _ensureOutputIsNotJsonRpcError(outputFile);
   }
 
   Future<void> runRasterizer(File outputFile) async {
@@ -125,8 +125,8 @@
     final IOSink sink = outputFile.openWrite();
     sink.add(base64.decode(response['screenshot']));
     await sink.close();
-    await showOutputFileInfo(outputFile);
-    await _ensureOutputIsNotJsonRpcError(outputFile);
+    _showOutputFileInfo(outputFile);
+    _ensureOutputIsNotJsonRpcError(outputFile);
   }
 
   Future<Map<String, dynamic>> _invokeVmServiceRpc(String method) async {
@@ -135,18 +135,20 @@
     return await vmService.vm.invokeRpcRaw(method);
   }
 
-  Future<void> _ensureOutputIsNotJsonRpcError(File outputFile) async {
-    if (await outputFile.length() < 1000) {
-      final String content = await outputFile.readAsString(
-        encoding: const AsciiCodec(allowInvalid: true),
-      );
-      if (content.startsWith('{"jsonrpc":"2.0", "error"'))
-        throwToolExit('\nIt appears the output file contains an error message, not valid skia output.');
+  void _ensureOutputIsNotJsonRpcError(File outputFile) {
+    if (outputFile.lengthSync() >= 1000) {
+      return;
+    }
+    final String content = outputFile.readAsStringSync(
+      encoding: const AsciiCodec(allowInvalid: true),
+    );
+    if (content.startsWith('{"jsonrpc":"2.0", "error"')) {
+      throwToolExit('It appears the output file contains an error message, not valid skia output.');
     }
   }
 
-  Future<void> showOutputFileInfo(File outputFile) async {
-    final int sizeKB = (await outputFile.length()) ~/ 1024;
+  void _showOutputFileInfo(File outputFile) {
+    final int sizeKB = (outputFile.lengthSync()) ~/ 1024;
     printStatus('Screenshot written to ${fs.path.relative(outputFile.path)} (${sizeKB}kB).');
   }
 }

diff --git a/packages/flutter_tools/lib/src/ios/mac.dart b/packages/flutter_tools/lib/src/ios/mac.dart
index f800f4c..ef8df16 100644
--- a/packages/flutter_tools/lib/src/ios/mac.dart
+++ b/packages/flutter_tools/lib/src/ios/mac.dart

@@ -269,7 +269,7 @@
   bool codesign = true,
   bool usesTerminalUi = true,
 }) async {
-  if (!await upgradePbxProjWithFlutterAssets(app.project))
+  if (!upgradePbxProjWithFlutterAssets(app.project))
     return XcodeBuildResult(success: false);
 
   if (!_checkXcodeVersion())
@@ -679,10 +679,10 @@
   manifest.writeAsStringSync(json.encode(jsonObject), mode: FileMode.write, flush: true);
 }
 
-Future<bool> upgradePbxProjWithFlutterAssets(IosProject project) async {
+bool upgradePbxProjWithFlutterAssets(IosProject project) {
   final File xcodeProjectFile = project.xcodeProjectInfoFile;
-  assert(await xcodeProjectFile.exists());
-  final List<String> lines = await xcodeProjectFile.readAsLines();
+  assert(xcodeProjectFile.existsSync());
+  final List<String> lines = xcodeProjectFile.readAsLinesSync();
 
   final RegExp oldAssets = RegExp(r'\/\* (flutter_assets|app\.flx)');
   final StringBuffer buffer = StringBuffer();
@@ -697,6 +697,6 @@
       buffer.writeln(line);
     }
   }
-  await xcodeProjectFile.writeAsString(buffer.toString());
+  xcodeProjectFile.writeAsStringSync(buffer.toString());
   return true;
 }

diff --git a/packages/flutter_tools/lib/src/macos/cocoapod_utils.dart b/packages/flutter_tools/lib/src/macos/cocoapod_utils.dart
index aa7f701..45e3fe9 100644
--- a/packages/flutter_tools/lib/src/macos/cocoapod_utils.dart
+++ b/packages/flutter_tools/lib/src/macos/cocoapod_utils.dart

@@ -38,9 +38,9 @@
     xcodeProject: xcodeProject,
     engineDir: flutterFrameworkDir(buildMode),
     isSwift: xcodeProject.isSwift,
-    dependenciesChanged: !await fingerprinter.doesFingerprintMatch(),
+    dependenciesChanged: !fingerprinter.doesFingerprintMatch(),
   );
   if (didPodInstall) {
-    await fingerprinter.writeFingerprint();
+    fingerprinter.writeFingerprint();
   }
 }

diff --git a/packages/flutter_tools/lib/src/macos/cocoapods.dart b/packages/flutter_tools/lib/src/macos/cocoapods.dart
index 9729387..ca2577f 100644
--- a/packages/flutter_tools/lib/src/macos/cocoapods.dart
+++ b/packages/flutter_tools/lib/src/macos/cocoapods.dart

@@ -106,7 +106,7 @@
     bool isSwift = false,
     bool dependenciesChanged = true,
   }) async {
-    if (!(await xcodeProject.podfile.exists())) {
+    if (!xcodeProject.podfile.existsSync()) {
       throwToolExit('Podfile missing');
     }
     if (await _checkPodCondition()) {

diff --git a/packages/flutter_tools/lib/src/resident_runner.dart b/packages/flutter_tools/lib/src/resident_runner.dart
index ac96adb..d5d8bbd 100644
--- a/packages/flutter_tools/lib/src/resident_runner.dart
+++ b/packages/flutter_tools/lib/src/resident_runner.dart

@@ -747,7 +747,7 @@
           }
         }
       }
-      final int sizeKB = (await outputFile.length()) ~/ 1024;
+      final int sizeKB = outputFile.lengthSync() ~/ 1024;
       status.stop();
       printStatus('Screenshot written to ${fs.path.relative(outputFile.path)} (${sizeKB}kB).');
     } catch (error) {

diff --git a/packages/flutter_tools/lib/src/runner/flutter_command_runner.dart b/packages/flutter_tools/lib/src/runner/flutter_command_runner.dart
index de8e4f9..5a16863 100644
--- a/packages/flutter_tools/lib/src/runner/flutter_command_runner.dart
+++ b/packages/flutter_tools/lib/src/runner/flutter_command_runner.dart

@@ -303,15 +303,15 @@
         ..writeln()
         ..writeln('# rest')
         ..writeln(topLevelResults.rest);
-      await manifest.writeAsString(buffer.toString(), flush: true);
+      manifest.writeAsStringSync(buffer.toString(), flush: true);
 
       // ZIP the recording up once the recording has been serialized.
-      addShutdownHook(() async {
+      addShutdownHook(() {
         final File zipFile = getUniqueFile(fs.currentDirectory, 'bugreport', 'zip');
         os.zip(tempDir, zipFile);
         printStatus(userMessages.runnerBugReportFinished(zipFile.basename));
       }, ShutdownStage.POST_PROCESS_RECORDING);
-      addShutdownHook(() => tempDir.delete(recursive: true), ShutdownStage.CLEANUP);
+      addShutdownHook(() => tempDir.deleteSync(recursive: true), ShutdownStage.CLEANUP);
     }
 
     assert(recordTo == null || replayFrom == null);
@@ -323,7 +323,7 @@
       contextOverrides.addAll(<Type, dynamic>{
         ProcessManager: getRecordingProcessManager(recordTo),
         FileSystem: getRecordingFileSystem(recordTo),
-        Platform: await getRecordingPlatform(recordTo),
+        Platform: getRecordingPlatform(recordTo),
       });
       VMService.enableRecordingConnection(recordTo);
     }
@@ -335,7 +335,7 @@
       contextOverrides.addAll(<Type, dynamic>{
         ProcessManager: await getReplayProcessManager(replayFrom),
         FileSystem: getReplayFileSystem(replayFrom),
-        Platform: await getReplayPlatform(replayFrom),
+        Platform: getReplayPlatform(replayFrom),
       });
       VMService.enableReplayConnection(replayFrom);
     }

diff --git a/packages/flutter_tools/lib/src/tracing.dart b/packages/flutter_tools/lib/src/tracing.dart
index 0a2de0c..f208305 100644
--- a/packages/flutter_tools/lib/src/tracing.dart
+++ b/packages/flutter_tools/lib/src/tracing.dart

@@ -78,12 +78,14 @@
   final File traceInfoFile = fs.file(traceInfoFilePath);
 
   // Delete old startup data, if any.
-  if (await traceInfoFile.exists())
-    await traceInfoFile.delete();
+  if (traceInfoFile.existsSync()) {
+    traceInfoFile.deleteSync();
+  }
 
   // Create "build" directory, if missing.
-  if (!(await traceInfoFile.parent.exists()))
-    await traceInfoFile.parent.create();
+  if (!traceInfoFile.parent.existsSync()) {
+    traceInfoFile.parent.createSync();
+  }
 
   final Tracing tracing = Tracing(observatory);
 

diff --git a/packages/flutter_tools/lib/src/version.dart b/packages/flutter_tools/lib/src/version.dart
index f1f4a42..61666df 100644
--- a/packages/flutter_tools/lib/src/version.dart
+++ b/packages/flutter_tools/lib/src/version.dart

@@ -99,8 +99,9 @@
   String get engineRevision => Cache.instance.engineRevision;
   String get engineRevisionShort => _shortGitRevision(engineRevision);
 
-  Future<void> ensureVersionFile() async {
+  Future<void> ensureVersionFile() {
     fs.file(fs.path.join(Cache.flutterRoot, 'version')).writeAsStringSync(_frameworkVersion);
+    return Future<void>.value();
   }
 
   @override

diff --git a/packages/flutter_tools/lib/src/vmservice_record_replay.dart b/packages/flutter_tools/lib/src/vmservice_record_replay.dart
index 9da5bf4..dcf04a2 100644
--- a/packages/flutter_tools/lib/src/vmservice_record_replay.dart
+++ b/packages/flutter_tools/lib/src/vmservice_record_replay.dart

@@ -24,7 +24,7 @@
 class RecordingVMServiceChannel extends DelegatingStreamChannel<String> {
   RecordingVMServiceChannel(StreamChannel<String> delegate, Directory location)
       : super(delegate) {
-    addShutdownHook(() async {
+    addShutdownHook(() {
       // Sort the messages such that they are ordered
       // `[request1, response1, request2, response2, ...]`. This serves no
       // purpose other than to make the serialized format more human-readable.
@@ -32,7 +32,7 @@
 
       final File file = _getManifest(location);
       final String json = const JsonEncoder.withIndent('  ').convert(_messages);
-      await file.writeAsString(json, flush: true);
+      file.writeAsStringSync(json, flush: true);
     }, ShutdownStage.SERIALIZE_RECORDING);
   }