Change all instance of throwing strings to throw specific error classes. (#97325)

packages/flutter_tools/analysis_options.yaml

@@ -7,7 +7,7 @@ linter:
     curly_braces_in_flow_control_structures: true
     library_private_types_in_public_api: false # Tool does not have any public API.
     no_runtimeType_toString: false # We use runtimeType for debugging in the tool.
-    only_throw_errors: false # For historical reasons we throw strings a lot.
+    only_throw_errors: true
     prefer_relative_imports: true
     public_member_api_docs: false # Tool does not have any public API.
     unawaited_futures: true

packages/flutter_tools/lib/src/commands/daemon.dart

@@ -212,13 +212,13 @@ class Daemon {
       final String method = request.data['method'] as String;
       assert(method != null);
       if (!method.contains('.')) {
-        throw 'method not understood: $method';
+        throw DaemonException('method not understood: $method');
       }
 
       final String prefix = method.substring(0, method.indexOf('.'));
       final String name = method.substring(method.indexOf('.') + 1);
       if (_domainMap[prefix] == null) {
-        throw 'no domain for method: $method';
+        throw DaemonException('no domain for method: $method');
       }
 
       _domainMap[prefix].handleCommand(name, id, castStringKeyedMap(request.data['params']) ?? const <String, dynamic>{}, request.binary);
@@ -275,7 +275,7 @@ abstract class Domain {
       } else if (_handlersWithBinary.containsKey(command)) {
         return _handlersWithBinary[command](args, binary);
       }
-      throw 'command not understood: $name.$command';
+      throw DaemonException('command not understood: $name.$command');
     }).then<dynamic>((dynamic result) {
       daemon.connection.sendResponse(id, _toJsonable(result));
     }).catchError((Object error, StackTrace stackTrace) {
@@ -289,33 +289,33 @@ abstract class Domain {
 
   String _getStringArg(Map<String, dynamic> args, String name, { bool required = false }) {
     if (required && !args.containsKey(name)) {
-      throw '$name is required';
+      throw DaemonException('$name is required');
     }
     final dynamic val = args[name];
     if (val != null && val is! String) {
-      throw '$name is not a String';
+      throw DaemonException('$name is not a String');
     }
     return val as String;
   }
 
   bool _getBoolArg(Map<String, dynamic> args, String name, { bool required = false }) {
     if (required && !args.containsKey(name)) {
-      throw '$name is required';
+      throw DaemonException('$name is required');
     }
     final dynamic val = args[name];
     if (val != null && val is! bool) {
-      throw '$name is not a bool';
+      throw DaemonException('$name is not a bool');
     }
     return val as bool;
   }
 
   int _getIntArg(Map<String, dynamic> args, String name, { bool required = false }) {
     if (required && !args.containsKey(name)) {
-      throw '$name is required';
+      throw DaemonException('$name is required');
     }
     final dynamic val = args[name];
     if (val != null && val is! int) {
-      throw '$name is not an int';
+      throw DaemonException('$name is not an int');
     }
     return val as int;
   }
@@ -670,7 +670,7 @@ class AppDomain extends Domain {
 
     final AppInstance app = _getApp(appId);
     if (app == null) {
-      throw "app '$appId' not found";
+      throw DaemonException("app '$appId' not found");
     }
 
     return _queueAndDebounceReloadAction(
@@ -728,7 +728,7 @@ class AppDomain extends Domain {
 
     final AppInstance app = _getApp(appId);
     if (app == null) {
-      throw "app '$appId' not found";
+      throw DaemonException("app '$appId' not found");
     }
     final FlutterDevice device = app.runner.flutterDevices.first;
     final List<FlutterView> views = await device.vmService.getFlutterViews();
@@ -741,7 +741,7 @@ class AppDomain extends Domain {
           .first.uiIsolate.id
       );
     if (result == null) {
-      throw 'method not available: $methodName';
+      throw DaemonException('method not available: $methodName');
     }
 
     if (result.containsKey('error')) {
@@ -756,7 +756,7 @@ class AppDomain extends Domain {
 
     final AppInstance app = _getApp(appId);
     if (app == null) {
-      throw "app '$appId' not found";
+      throw DaemonException("app '$appId' not found");
     }
 
     return app.stop().then<bool>(
@@ -775,7 +775,7 @@ class AppDomain extends Domain {
 
     final AppInstance app = _getApp(appId);
     if (app == null) {
-      throw "app '$appId' not found";
+      throw DaemonException("app '$appId' not found");
     }
 
     return app.detach().then<bool>(
@@ -903,7 +903,7 @@ class DeviceDomain extends Domain {
 
     final Device device = await daemon.deviceDomain._getDevice(deviceId);
     if (device == null) {
-      throw "device '$deviceId' not found";
+      throw DaemonException("device '$deviceId' not found");
     }
 
     hostPort = await device.portForwarder.forward(devicePort, hostPort: hostPort);
@@ -919,7 +919,7 @@ class DeviceDomain extends Domain {
 
     final Device device = await daemon.deviceDomain._getDevice(deviceId);
     if (device == null) {
-      throw "device '$deviceId' not found";
+      throw DaemonException("device '$deviceId' not found");
     }
 
     return device.portForwarder.unforward(ForwardedPort(hostPort, devicePort));
@@ -930,7 +930,7 @@ class DeviceDomain extends Domain {
     final String deviceId = _getStringArg(args, 'deviceId', required: true);
     final Device device = await daemon.deviceDomain._getDevice(deviceId);
     if (device == null) {
-      throw "device '$deviceId' not found";
+      throw DaemonException("device '$deviceId' not found");
     }
     final String buildMode = _getStringArg(args, 'buildMode', required: true);
     return await device.supportsRuntimeMode(getBuildModeForName(buildMode));
@@ -954,7 +954,7 @@ class DeviceDomain extends Domain {
     final String deviceId = _getStringArg(args, 'deviceId', required: true);
     final Device device = await daemon.deviceDomain._getDevice(deviceId);
     if (device == null) {
-      throw "device '$deviceId' not found";
+      throw DaemonException("device '$deviceId' not found");
     }
     final String applicationPackageId = _getStringArg(args, 'applicationPackageId');
     final ApplicationPackage applicationPackage = applicationPackageId != null ? _applicationPackages[applicationPackageId] : null;
@@ -979,7 +979,7 @@ class DeviceDomain extends Domain {
     final String deviceId = _getStringArg(args, 'deviceId', required: true);
     final Device device = await daemon.deviceDomain._getDevice(deviceId);
     if (device == null) {
-      throw "device '$deviceId' not found";
+      throw DaemonException("device '$deviceId' not found");
     }
     final String applicationPackageId = _getStringArg(args, 'applicationPackageId', required: true);
     final ApplicationPackage applicationPackage = _applicationPackages[applicationPackageId];
@@ -1009,7 +1009,7 @@ class DeviceDomain extends Domain {
     final String deviceId = _getStringArg(args, 'deviceId', required: true);
     final Device device = await daemon.deviceDomain._getDevice(deviceId);
     if (device == null) {
-      throw "device '$deviceId' not found";
+      throw DaemonException("device '$deviceId' not found");
     }
     final String applicationPackageId = _getStringArg(args, 'applicationPackageId', required: true);
     final ApplicationPackage applicationPackage = _applicationPackages[applicationPackageId];
@@ -1024,7 +1024,7 @@ class DeviceDomain extends Domain {
     final String deviceId = _getStringArg(args, 'deviceId', required: true);
     final Device device = await daemon.deviceDomain._getDevice(deviceId);
     if (device == null) {
-      throw "device '$deviceId' not found";
+      throw DaemonException("device '$deviceId' not found");
     }
     final String tempFileName = 'screenshot_${_id++}';
     final File tempFile = daemon.proxyDomain.tempDirectory.childFile(tempFileName);
@@ -1298,9 +1298,9 @@ class EmulatorDomain extends Domain {
     final List<Emulator> matches =
         await emulators.getEmulatorsMatching(emulatorId);
     if (matches.isEmpty) {
-      throw "emulator '$emulatorId' not found";
+      throw DaemonException("emulator '$emulatorId' not found");
     } else if (matches.length > 1) {
-      throw "multiple emulators match '$emulatorId'";
+      throw DaemonException("multiple emulators match '$emulatorId'");
     } else {
       await matches.first.launch(coldBoot: coldBoot);
     }
@@ -1556,3 +1556,13 @@ class DebounceOperationQueue<T, K> {
     return completer.future;
   }
 }
+
+/// Specialized exception for returning errors to the daemon client.
+class DaemonException implements Exception {
+  DaemonException(this.message);
+
+  final String message;
+
+  @override
+  String toString() => message;
+}

packages/flutter_tools/lib/src/commands/update_packages.dart

@@ -249,12 +249,7 @@ class UpdatePackagesCommand extends FlutterCommand {
     bool needsUpdate = false;
     globals.printStatus('Verifying pubspecs...');
     for (final Directory directory in packages) {
-      PubspecYaml pubspec;
-      try {
-        pubspec = PubspecYaml(directory);
-      } on String catch (message) {
-        throwToolExit(message);
-      }
+      final PubspecYaml pubspec = PubspecYaml(directory);
       globals.printTrace('Reading pubspec.yaml from ${directory.path}');
       if (pubspec.checksum.value == null) {
         // If the checksum is invalid or missing, we can just ask them run to run
@@ -310,12 +305,7 @@ class UpdatePackagesCommand extends FlutterCommand {
       if (doUpgrade) {
         globals.printTrace('Reading pubspec.yaml from: ${directory.path}');
       }
-      PubspecYaml pubspec;
-      try {
-        pubspec = PubspecYaml(directory); // this parses the pubspec.yaml
-      } on String catch (message) {
-        throwToolExit(message);
-      }
+      final PubspecYaml pubspec = PubspecYaml(directory); // this parses the pubspec.yaml
       pubspecs.add(pubspec); // remember it for later
       for (final PubspecDependency dependency in pubspec.allDependencies) {
         if (allDependencies.containsKey(dependency.name)) {
@@ -721,19 +711,19 @@ class PubspecYaml {
             // If we're entering the "dependencies" section, we want to make sure that
             // it's the first section (of those we care about) that we've seen so far.
             if (seenMain) {
-              throw 'Two dependencies sections found in $filename. There should only be one.';
+              throwToolExit('Two dependencies sections found in $filename. There should only be one.');
             }
             if (seenDev) {
-              throw 'The dependencies section was after the dev_dependencies section in $filename. '
+              throwToolExit('The dependencies section was after the dev_dependencies section in $filename. '
                     'To enable one-pass processing, the dependencies section must come before the '
-                    'dev_dependencies section.';
+                    'dev_dependencies section.');
             }
             seenMain = true;
           } else if (section == Section.devDependencies) {
             // Similarly, if we're entering the dev_dependencies section, we should verify
             // that we've not seen one already.
             if (seenDev) {
-              throw 'Two dev_dependencies sections found in $filename. There should only be one.';
+              throwToolExit('Two dev_dependencies sections found in $filename. There should only be one.');
             }
             seenDev = true;
           }
@@ -774,7 +764,7 @@ class PubspecYaml {
               // First, make sure it's a unique dependency. Listing dependencies
               // twice doesn't make sense.
               if (masterDependencies.containsKey(dependency.name)) {
-                throw '$filename contains two dependencies on ${dependency.name}.';
+                throwToolExit('$filename contains two dependencies on ${dependency.name}.');
               }
               masterDependencies[dependency.name] = dependency;
             } else {
@@ -1306,7 +1296,7 @@ class PubspecDependency extends PubspecLine {
       _kind = DependencyKind.git;
       return false;
     } else {
-      throw 'Could not parse additional details for dependency $name; line was: "$line"';
+      throwToolExit('Could not parse additional details for dependency $name; line was: "$line"');
     }
     _lockIsOverride = lockIsOverride;
     _lockLine = line;

packages/flutter_tools/lib/src/fuchsia/fuchsia_device.dart

@@ -536,16 +536,16 @@ class FuchsiaDevice extends Device {
   @override
   Future<void> takeScreenshot(File outputFile) async {
     if (outputFile.basename.split('.').last != 'ppm') {
-      throw '${outputFile.path} must be a .ppm file';
+      throw Exception('${outputFile.path} must be a .ppm file');
     }
     final RunResult screencapResult = await shell('screencap > /tmp/screenshot.ppm');
     if (screencapResult.exitCode != 0) {
-      throw 'Could not take a screenshot on device $name:\n$screencapResult';
+      throw Exception('Could not take a screenshot on device $name:\n$screencapResult');
     }
     try {
       final RunResult scpResult = await scp('/tmp/screenshot.ppm', outputFile.path);
       if (scpResult.exitCode != 0) {
-        throw 'Failed to copy screenshot from device:\n$scpResult';
+        throw Exception('Failed to copy screenshot from device:\n$scpResult');
       }
     } finally {
       try {

packages/flutter_tools/lib/src/localizations/localizations_utils.dart

@@ -156,7 +156,7 @@ Map<String, List<String>> _parseSection(String section) {
     }
     final int colon = line.indexOf(':');
     if (colon <= 0) {
-      throw 'not sure how to deal with "$line"';
+      throw Exception('not sure how to deal with "$line"');
     }
     final String name = line.substring(0, colon);
     final String value = line.substring(colon + 2);

packages/flutter_tools/lib/src/proxied_devices/devices.dart

@@ -195,7 +195,7 @@ class ProxiedDevice extends Device {
   _ProxiedPortForwarder get proxiedPortForwarder => _proxiedPortForwarder ??= _ProxiedPortForwarder(connection, logger: _logger);
 
   @override
-  DevicePortForwarder get portForwarder => throw UnimplementedError;
+  DevicePortForwarder get portForwarder => throw UnimplementedError();
 
   @override
   void clearLogs() => throw UnimplementedError();

packages/flutter_tools/lib/src/resident_runner.dart

@@ -633,7 +633,7 @@ abstract class ResidentHandlers {
   /// the value of [fullRestart].
   Future<OperationResult> restart({ bool fullRestart = false, bool pause = false, String reason }) {
     final String mode = isRunningProfile ? 'profile' :isRunningRelease ? 'release' : 'this';
-    throw '${fullRestart ? 'Restart' : 'Reload'} is not supported in $mode mode';
+    throw Exception('${fullRestart ? 'Restart' : 'Reload'} is not supported in $mode mode');
   }
 
   /// Dump the application's current widget tree to the terminal.
@@ -1280,7 +1280,7 @@ abstract class ResidentRunner extends ResidentHandlers {
     @required bool allowExistingDdsInstance,
   }) async {
     if (!debuggingOptions.debuggingEnabled) {
-      throw 'The service protocol is not enabled.';
+      throw Exception('The service protocol is not enabled.');
     }
     _finished = Completer<int>();
     // Listen for service protocol connection to close.

packages/flutter_tools/lib/src/run_cold.dart

@@ -87,8 +87,8 @@ class ColdRunner extends ResidentRunner {
     if (debuggingEnabled) {
       try {
         await connectToServiceProtocol(allowExistingDdsInstance: false);
-      } on String catch (message) {
-        globals.printError(message);
+      } on Exception catch (exception) {
+        globals.printError(exception.toString());
         appFailedToStart();
         return 2;
       }

packages/flutter_tools/lib/src/run_hot.dart

@@ -219,7 +219,7 @@ class HotRunner extends ResidentRunner {
         }
       }
     }
-    throw 'Failed to compile $expression';
+    throw Exception('Failed to compile $expression');
   }
 
   // Returns the exit code of the flutter tool process, like [run].

packages/flutter_tools/lib/src/test/flutter_platform.dart

@@ -388,7 +388,7 @@ class FlutterPlatform extends PlatformPlugin {
     bool isStatic,
   ) async {
     if (compiler == null || compiler.compiler == null) {
-      throw 'Compiler is not set up properly to compile $expression';
+      throw Exception('Compiler is not set up properly to compile $expression');
     }
     final CompilerOutput compilerOutput =
       await compiler.compiler.compileExpression(expression, definitions,
@@ -396,7 +396,7 @@ class FlutterPlatform extends PlatformPlugin {
     if (compilerOutput != null && compilerOutput.expressionData != null) {
       return base64.encode(compilerOutput.expressionData);
     }
-    throw 'Failed to compile $expression';
+    throw Exception('Failed to compile $expression');
   }
 
   TestDevice _createTestDevice(int ourTestCount) {

packages/flutter_tools/test/commands.shard/hermetic/daemon_test.dart

@@ -660,7 +660,7 @@ void main() {
       bool isRunning = false;
       Future<int> f(int ret) async {
         if (isRunning) {
-          throw 'Functions ran concurrently!';
+          throw Exception('Functions ran concurrently!');
         }
         isRunning = true;
         await Future<void>.delayed(debounceDuration * 2);

packages/flutter_tools/test/commands.shard/hermetic/doctor_test.dart

@@ -346,7 +346,7 @@ void main() {
               '[☠] Crashing validator (the doctor check crashed)\n'
               '    ✗ Due to an error, the doctor check did not complete. If the error message below is not helpful, '
               'please let us know about this issue at https://github.com/flutter/flutter/issues.\n'
-              '    ✗ fatal error\n'
+              '    ✗ Bad state: fatal error\n'
               '[✓] Validators are fun (with statusInfo)\n'
               '[✓] Four score and seven validators ago (with statusInfo)\n'
               '\n'
@@ -378,7 +378,7 @@ void main() {
               '[☠] Async crashing validator (the doctor check crashed)\n'
               '    ✗ Due to an error, the doctor check did not complete. If the error message below is not helpful, '
               'please let us know about this issue at https://github.com/flutter/flutter/issues.\n'
-              '    ✗ fatal error\n'
+              '    ✗ Bad state: fatal error\n'
               '[✓] Validators are fun (with statusInfo)\n'
               '[✓] Four score and seven validators ago (with statusInfo)\n'
               '\n'
@@ -848,7 +848,7 @@ class CrashingValidator extends DoctorValidator {
 
   @override
   Future<ValidationResult> validate() async {
-    throw 'fatal error';
+    throw StateError('fatal error');
   }
 }
 
@@ -862,7 +862,7 @@ class AsyncCrashingValidator extends DoctorValidator {
     const Duration delay = Duration(seconds: 1);
     final Future<ValidationResult> result = Future<ValidationResult>.delayed(delay)
       .then((_) {
-        throw 'fatal error';
+        throw StateError('fatal error');
       });
     _time.elapse(const Duration(seconds: 1));
     _time.flushMicrotasks();

packages/flutter_tools/test/general.shard/android/android_device_test.dart

@@ -260,7 +260,7 @@ flutter:
       ]),
       androidConsoleSocketFactory: (String host, int port) async {
         socketWasCreated = true;
-        throw 'Socket was created for non-emulator';
+        throw Exception('Socket was created for non-emulator');
       }
     );
 
@@ -279,7 +279,7 @@ flutter:
       ]),
       androidConsoleSocketFactory: (String host, int port) async {
         socketWasCreated = true;
-        throw 'Socket was created for emulator without port in ID';
+        throw Exception('Socket was created for emulator without port in ID');
       },
     );
 
@@ -664,7 +664,7 @@ class FakeWorkingAndroidConsoleSocket extends Fake implements Socket {
       // as part of the previous text to ensure both are handled.
       _controller.add('OK\n');
     } else {
-      throw 'Unexpected command $text';
+      throw Exception('Unexpected command $text');
     }
   }
 

packages/flutter_tools/test/general.shard/base/async_guard_test.dart

@@ -13,25 +13,36 @@ import '../../src/common.dart';
 Future<void> asyncError() {
   final Completer<void> completer = Completer<void>();
   final Completer<void> errorCompleter = Completer<void>();
-  errorCompleter.completeError('Async Doom', StackTrace.current);
+  errorCompleter.completeError(_CustomException('Async Doom'), StackTrace.current);
   return completer.future;
 }
 
+/// Specialized exception to be caught.
+class _CustomException implements Exception {
+  _CustomException(this.message);
+
+  final String message;
+
+  @override
+  String toString() => message;
+}
+
+
 Future<void> syncError() {
-  throw 'Sync Doom';
+  throw _CustomException('Sync Doom');
 }
 
 Future<void> syncAndAsyncError() {
   final Completer<void> errorCompleter = Completer<void>();
-  errorCompleter.completeError('Async Doom', StackTrace.current);
-  throw 'Sync Doom';
+  errorCompleter.completeError(_CustomException('Async Doom'), StackTrace.current);
+  throw _CustomException('Sync Doom');
 }
 
 Future<void> delayedThrow(FakeAsync time) {
   final Future<void> result =
     Future<void>.delayed(const Duration(milliseconds: 10))
       .then((_) async {
-        throw 'Delayed Doom';
+        throw _CustomException('Delayed Doom');
       });
   time.elapse(const Duration(seconds: 1));
   time.flushMicrotasks();
@@ -69,7 +80,7 @@ void main() {
       try {
         // Completer is required or else we timeout.
         await Future.any(<Future<void>>[asyncError(), caughtInZone.future]);
-      } on String {
+      } on _CustomException {
         caughtByHandler = true;
       }
     });
@@ -83,7 +94,7 @@ void main() {
       try {
         // Completer is required or else we timeout.
         await Future.any(<Future<void>>[syncAndAsyncError(), caughtInZone.future]);
-      } on String {
+      } on _CustomException {
         caughtByHandler = true;
       }
     });
@@ -96,7 +107,7 @@ void main() {
     await zone.run(() async {
       try {
         await syncError();
-      } on String {
+      } on _CustomException {
         caughtByHandler = true;
       }
     });
@@ -109,7 +120,7 @@ void main() {
     await zone.run(() async {
       try {
         await asyncGuard(syncError);
-      } on String {
+      } on _CustomException {
         caughtByHandler = true;
       }
     });
@@ -123,7 +134,7 @@ void main() {
     await zone.run(() async {
       try {
         await asyncGuard(asyncError);
-      } on String {
+      } on _CustomException {
         caughtByHandler = true;
       }
     });
@@ -136,7 +147,7 @@ void main() {
     await zone.run(() async {
       try {
         await asyncGuard(syncAndAsyncError);
-      } on String {
+      } on _CustomException {
         caughtByHandler = true;
       }
     });
@@ -159,7 +170,7 @@ void main() {
           });
         try {
           await f;
-        } on String {
+        } on _CustomException {
           caughtByHandler = true;
         }
         if (!completer.isCompleted) {
@@ -197,7 +208,7 @@ void main() {
         );
         try {
           await f;
-        } on String {
+        } on _CustomException {
           caughtByHandler = true;
         }
         if (!completer.isCompleted) {
@@ -235,7 +246,7 @@ void main() {
         );
         try {
           await f;
-        } on String {
+        } on _CustomException {
           caughtByHandler = true;
         }
         if (!completer.isCompleted) {
@@ -275,7 +286,7 @@ void main() {
         );
         try {
           await f;
-        } on String {
+        } on _CustomException {
           caughtByHandler = true;
         }
         if (!completer.isCompleted) {

packages/flutter_tools/test/general.shard/base/error_handling_io_test.dart

@@ -1240,7 +1240,7 @@ class ThrowsOnCurrentDirectoryFileSystem extends Fake implements FileSystem {
 }
 
 class FakeExistsFile extends Fake implements File {
-  late Object error;
+  late Exception error;
   int existsCount = 0;
 
 

packages/flutter_tools/test/general.shard/base/logger_test.dart

@@ -1267,7 +1267,7 @@ void main() {
 /// A fake [Logger] that throws the [Invocation] for any method call.
 class FakeLogger implements Logger {
   @override
-  dynamic noSuchMethod(Invocation invocation) => throw invocation;
+  dynamic noSuchMethod(Invocation invocation) => throw invocation; // ignore: only_throw_errors
 }
 
 /// Returns the [Invocation] thrown from a call to [FakeLogger].
@@ -1309,14 +1309,14 @@ class FakeStdout extends Fake implements Stdout {
   @override
   void write(Object object) {
     if (syncError) {
-      throw 'Error!';
+      throw Exception('Error!');
     }
     Zone.current.runUnaryGuarded<void>((_) {
       if (completeWithError) {
         _completer.completeError(Exception('Some pipe error'));
       } else {
         _completer.complete();
-        throw 'Error!';
+        throw Exception('Error!');
       }
     }, null);
   }

packages/flutter_tools/test/general.shard/crash_reporting_test.dart

@@ -381,7 +381,7 @@ class MockCrashReportSender extends MockClient {
 }
 
 class CrashingCrashReportSender extends MockClient {
-  CrashingCrashReportSender(Object exception) : super((Request request) async {
+  CrashingCrashReportSender(Exception exception) : super((Request request) async {
     throw exception;
   });
 }

packages/flutter_tools/test/general.shard/devfs_test.dart

@@ -519,7 +519,7 @@ void main() {
           } else if (boundaryKey != null && stringData.startsWith(boundaryKey)) {
             yield utf8.encode('result abc2\nline1\nline2\nabc2\nabc2 lib/foo.txt.dill 0\n');
           } else {
-            throw 'Saw $data ($stringData)';
+            throw Exception('Saw $data ($stringData)');
           }
           processed++;
         }

packages/flutter_tools/test/general.shard/fuchsia/fuchsia_device_test.dart

@@ -440,7 +440,11 @@ void main() {
       final FuchsiaDevice device = FuchsiaDevice('id', name: 'tester');
       await expectLater(
         () => device.takeScreenshot(globals.fs.file('file.invalid')),
-        throwsA(equals('file.invalid must be a .ppm file')),
+        throwsA(isA<Exception>().having(
+          (Exception exception) => exception.toString(),
+          'message',
+          contains('file.invalid must be a .ppm file')
+        )),
       );
     });
 
@@ -460,7 +464,11 @@ void main() {
 
       await expectLater(
         () => device.takeScreenshot(globals.fs.file('file.ppm')),
-        throwsA(equals('Could not take a screenshot on device tester:\n<error-message>')),
+        throwsA(isA<Exception>().having(
+          (Exception exception) => exception.toString(),
+          'message',
+          contains('Could not take a screenshot on device tester:\n<error-message>')
+        )),
       );
     }, overrides: <Type, Generator>{
       ProcessManager: () => processManager,
@@ -506,7 +514,11 @@ void main() {
 
       await expectLater(
         () => device.takeScreenshot(globals.fs.file('file.ppm')),
-        throwsA(equals('Failed to copy screenshot from device:\n<error-message>')),
+        throwsA(isA<Exception>().having(
+          (Exception exception) => exception.toString(),
+          'message',
+          contains('Failed to copy screenshot from device:\n<error-message>')
+        )),
       );
     }, overrides: <Type, Generator>{
       ProcessManager: () => processManager,

packages/flutter_tools/test/general.shard/hot_test.dart

@@ -465,7 +465,7 @@ void main() {
         final List<FlutterDevice> devices = <FlutterDevice>[
           fakeFlutterDevice,
         ];
-        fakeFlutterDevice.updateDevFSReportCallback = () async => throw 'updateDevFS failed';
+        fakeFlutterDevice.updateDevFSReportCallback = () async => throw Exception('updateDevFS failed');
 
         final HotRunner runner = HotRunner(
           devices,
@@ -474,7 +474,7 @@ void main() {
           devtoolsHandler: createNoOpHandler,
         );
 
-        await expectLater(runner.restart(fullRestart: true), throwsA('updateDevFS failed'));
+        await expectLater(runner.restart(fullRestart: true), throwsA(isA<Exception>().having((Exception e) => e.toString(), 'message', 'Exception: updateDevFS failed')));
         expect(testingConfig.updateDevFSCompleteCalled, true);
       }, overrides: <Type, Generator>{
         HotRunnerConfig: () => testingConfig,
@@ -499,7 +499,7 @@ void main() {
         final List<FlutterDevice> devices = <FlutterDevice>[
           fakeFlutterDevice,
         ];
-        fakeFlutterDevice.updateDevFSReportCallback = () async => throw 'updateDevFS failed';
+        fakeFlutterDevice.updateDevFSReportCallback = () async => throw Exception('updateDevFS failed');
 
         final HotRunner runner = HotRunner(
           devices,
@@ -508,7 +508,7 @@ void main() {
           devtoolsHandler: createNoOpHandler,
         );
 
-        await expectLater(runner.restart(), throwsA('updateDevFS failed'));
+        await expectLater(runner.restart(), throwsA(isA<Exception>().having((Exception e) => e.toString(), 'message', 'Exception: updateDevFS failed')));
         expect(testingConfig.updateDevFSCompleteCalled, true);
       }, overrides: <Type, Generator>{
         HotRunnerConfig: () => testingConfig,

packages/flutter_tools/test/general.shard/project_test.dart

@@ -925,7 +925,7 @@ void transfer(FileSystemEntity entity, FileSystem target) {
   } else if (entity is File) {
     target.file(entity.absolute.path).writeAsBytesSync(entity.readAsBytesSync(), flush: true);
   } else {
-    throw 'Unsupported FileSystemEntity ${entity.runtimeType}';
+    throw Exception('Unsupported FileSystemEntity ${entity.runtimeType}');
   }
 }
 

packages/flutter_tools/test/general.shard/protocol_discovery_test.dart

@@ -405,11 +405,11 @@ class MockPortForwarder extends DevicePortForwarder {
   }
 
   @override
-  List<ForwardedPort> get forwardedPorts => throw 'not implemented';
+  List<ForwardedPort> get forwardedPorts => throw UnimplementedError();
 
   @override
   Future<void> unforward(ForwardedPort forwardedPort) {
-    throw 'not implemented';
+    throw UnimplementedError();
   }
 
   @override

packages/flutter_tools/test/general.shard/resident_runner_test.dart

@@ -2142,8 +2142,8 @@ class FakeFlutterDevice extends Fake implements FlutterDevice {
     success: true,
     invalidatedSourcesCount: 1,
   );
-  Object reportError;
-  Object runColdError;
+  Exception reportError;
+  Exception runColdError;
   int runHotCode = 0;
   int runColdCode = 0;
 

packages/flutter_tools/test/general.shard/resident_web_runner_test.dart

@@ -1225,6 +1225,8 @@ class FakeWebDevFS extends Fake implements WebDevFS {
   @override
   Future<ConnectionResult> connect(bool useDebugExtension) async {
     if (exception != null) {
+      assert(exception is Exception || exception is Error);
+      // ignore: only_throw_errors, exception is either Error or Exception here.
       throw exception;
     }
     return result;
@@ -1299,7 +1301,7 @@ class FakeFlutterDevice extends Fake implements FlutterDevice {
     success: true,
     invalidatedSourcesCount: 1,
   );
-  Object reportError;
+  Exception reportError;
 
   @override
   ResidentCompiler generator;

packages/flutter_tools/test/general.shard/runner/runner_test.dart

@@ -44,7 +44,7 @@ void main() {
         // TODO(jamesderlin): Ideally only the first call to exit() would be
         // honored and subsequent calls would be no-ops, but existing tests
         // rely on all calls to throw.
-        throw 'test exit';
+        throw Exception('test exit');
       });
 
       Cache.disableLocking();
@@ -75,7 +75,7 @@ void main() {
         onError: (Object error, StackTrace stack) { // ignore: deprecated_member_use
           expect(firstExitCode, isNotNull);
           expect(firstExitCode, isNot(0));
-          expect(error, 'test exit');
+          expect(error.toString(), 'Exception: test exit');
           completer.complete();
         },
       ));
@@ -88,7 +88,7 @@ void main() {
       // *original* crash, and not the crash from the first crash report
       // attempt.
       final CrashingUsage crashingUsage = globals.flutterUsage as CrashingUsage;
-      expect(crashingUsage.sentException, 'an exception % --');
+      expect(crashingUsage.sentException.toString(), 'Exception: an exception % --');
     }, overrides: <Type, Generator>{
       Platform: () => FakePlatform(environment: <String, String>{
         'FLUTTER_ANALYTICS_LOG_FILE': 'test',
@@ -127,7 +127,7 @@ void main() {
         onError: (Object error, StackTrace stack) { // ignore: deprecated_member_use
           expect(firstExitCode, isNotNull);
           expect(firstExitCode, isNot(0));
-          expect(error, 'test exit');
+          expect(error.toString(), 'Exception: test exit');
           completer.complete();
         },
       ));
@@ -174,7 +174,7 @@ void main() {
         onError: (Object error, StackTrace stack) { // ignore: deprecated_member_use
           expect(firstExitCode, isNotNull);
           expect(firstExitCode, isNot(0));
-          expect(error, 'test exit');
+          expect(error.toString(), 'Exception: test exit');
           completer.complete();
         },
       ));
@@ -183,20 +183,20 @@ void main() {
       final String errorText = testLogger.errorText;
       expect(
         errorText,
-        containsIgnoringWhitespace('Oops; flutter has exited unexpectedly: "an exception % --".\n'),
+        containsIgnoringWhitespace('Oops; flutter has exited unexpectedly: "Exception: an exception % --".\n'),
       );
 
       final File log = globals.fs.file('/flutter_01.log');
       final String logContents = log.readAsStringSync();
       expect(logContents, contains(kCustomBugInstructions));
       expect(logContents, contains('flutter crash'));
-      expect(logContents, contains('String: an exception % --'));
+      expect(logContents, contains('Exception: an exception % --'));
       expect(logContents, contains('CrashingFlutterCommand.runCommand'));
       expect(logContents, contains('[✓] Flutter'));
 
       final CrashDetails sentDetails = (globals.crashReporter as WaitingCrashReporter)._details;
       expect(sentDetails.command, 'flutter crash');
-      expect(sentDetails.error, 'an exception % --');
+      expect(sentDetails.error.toString(), 'Exception: an exception % --');
       expect(sentDetails.stackTrace.toString(), contains('CrashingFlutterCommand.runCommand'));
       expect(await sentDetails.doctorText.text, contains('[✓] Flutter'));
     }, overrides: <Type, Generator>{
@@ -234,7 +234,7 @@ class CrashingFlutterCommand extends FlutterCommand {
 
   @override
   Future<FlutterCommandResult> runCommand() async {
-    const String error = 'an exception % --'; // Test URL encoding.
+    final Exception error = Exception('an exception % --'); // Test URL encoding.
     if (!_asyncCrash) {
       throw error;
     }
@@ -270,7 +270,7 @@ class CrashingUsage implements Usage {
   void sendException(dynamic exception) {
     if (_firstAttempt) {
       _firstAttempt = false;
-      throw 'CrashingUsage.sendException';
+      throw Exception('CrashingUsage.sendException');
     }
     _sentException = exception;
   }

packages/flutter_tools/test/integration.shard/debug_adapter/test_client.dart

@@ -76,7 +76,7 @@ class DapTestClient {
   /// Returns a Future that completes with the next [event] event.
   Future<Event> event(String event) => _eventController.stream.firstWhere(
       (Event e) => e.event == event,
-      orElse: () => throw 'Did not receive $event event before stream closed');
+      orElse: () => throw Exception('Did not receive $event event before stream closed'));
 
   /// Returns a stream for [event] events.
   Stream<Event> events(String event) {
@@ -190,13 +190,13 @@ class DapTestClient {
   /// event for [extension].
   Future<Map<String, Object?>> serviceExtensionAdded(String extension) => serviceExtensionAddedEvents.firstWhere(
       (Map<String, Object?> body) => body['extensionRPC'] == extension,
-      orElse: () => throw 'Did not receive $extension extension added event before stream closed');
+      orElse: () => throw Exception('Did not receive $extension extension added event before stream closed'));
 
   /// Returns a Future that completes with the next serviceExtensionStateChanged
   /// event for [extension].
   Future<Map<String, Object?>> serviceExtensionStateChanged(String extension) => serviceExtensionStateChangedEvents.firstWhere(
       (Map<String, Object?> body) => body['extension'] == extension,
-      orElse: () => throw 'Did not receive $extension extension state changed event before stream closed');
+      orElse: () => throw Exception('Did not receive $extension extension state changed event before stream closed'));
 
   /// Initializes the debug adapter and launches [program]/[cwd] or calls the
   /// custom [launch] method.

packages/flutter_tools/test/integration.shard/debug_adapter/test_server.dart

@@ -81,14 +81,14 @@ class OutOfProcessDapTestServer extends DapTestServer {
         .listen((String error) {
       logger?.call(error);
       if (!_isShuttingDown) {
-        throw error;
+        throw Exception(error);
       }
     });
     unawaited(_process.exitCode.then((int code) {
       final String message = 'Out-of-process DAP server terminated with code $code';
       logger?.call(message);
       if (!_isShuttingDown && code != 0) {
-        throw message;
+        throw Exception(message);
       }
     }));
   }

packages/flutter_tools/test/integration.shard/hot_reload_errors_test.dart

@@ -31,6 +31,6 @@ void main() {
     await flutter.run();
     project.removeFieldFromConstClass();
 
-    expect(flutter.hotReload(), throwsA(contains('Try performing a hot restart instead.')));
+    expect(flutter.hotReload(), throwsA(isA<Exception>().having((Exception e) => e.toString(), 'message', contains('Try performing a hot restart instead.'))));
   });
 }

packages/flutter_tools/test/integration.shard/test_driver.dart

@@ -482,7 +482,7 @@ abstract class FlutterTestDriver {
         timeoutExpired = true;
         _debugPrint(messages.toString());
       }
-      throw error;
+      throw error; // ignore: only_throw_errors
     }).whenComplete(() => subscription.cancel());
   }
 }
@@ -753,7 +753,7 @@ class FlutterRunTestDriver extends FlutterTestDriver {
   }
 
   void _throwErrorResponse(String message) {
-    throw '$message\n\n$_lastResponse\n\n${_errorBuffer.toString()}'.trim();
+    throw Exception('$message\n\n$_lastResponse\n\n${_errorBuffer.toString()}'.trim());
   }
 
   final bool spawnDdsInstance;

packages/flutter_tools/test/src/context.dart

@@ -153,7 +153,7 @@ void testUsingContext(
             print(error); // ignore: avoid_print
             print(stackTrace); // ignore: avoid_print
             _printBufferedErrors(context);
-            throw error;
+            throw error; //ignore: only_throw_errors
           });
         },
       );
@@ -348,10 +348,10 @@ class LocalFileSystemBlockingSetCurrentDirectory extends LocalFileSystem {
 
   @override
   set currentDirectory(dynamic value) {
-    throw 'globals.fs.currentDirectory should not be set on the local file system during '
+    throw Exception('globals.fs.currentDirectory should not be set on the local file system during '
           'tests as this can cause race conditions with concurrent tests. '
           'Consider using a MemoryFileSystem for testing if possible or refactor '
-          'code to not require setting globals.fs.currentDirectory.';
+          'code to not require setting globals.fs.currentDirectory.');
   }
 }
 

packages/flutter_tools/test/src/fake_process_manager.dart

@@ -258,7 +258,8 @@ abstract class FakeProcessManager implements ProcessManager {
     _pid += 1;
     final FakeCommand fakeCommand = findCommand(command, workingDirectory, environment, encoding);
     if (fakeCommand.exception != null) {
-      throw fakeCommand.exception!;
+      assert(fakeCommand.exception is Exception || fakeCommand.exception is Error);
+      throw fakeCommand.exception!; // ignore: only_throw_errors
     }
     if (fakeCommand.onRun != null) {
       fakeCommand.onRun!();

packages/flutter_tools/test/src/test_build_system.dart

@@ -27,7 +27,7 @@ class TestBuildSystem implements BuildSystem {
 
   final List<BuildResult> _results;
   final BuildResult? _singleResult;
-  final Object? _exception;
+  final Exception? _exception;
   final void Function(Target target, Environment environment)? _onRun;
   int _nextResult = 0;