Adds tool warning log level and command line options to fail on warning/error output (#92031)

dev/bots/test.dart

@@ -170,6 +170,7 @@ Future<void> main(List<String> args) async {
   try {
     flutterTestArgs.addAll(args);
     final Set<String> removeArgs = <String>{};
+    bool runSmokeTests = true;
     for (final String arg in args) {
       if (arg.startsWith('--local-engine=')) {
         localEngineEnv['FLUTTER_LOCAL_ENGINE'] = arg.substring('--local-engine='.length);
@@ -181,12 +182,18 @@ Future<void> main(List<String> args) async {
         _shuffleSeed = arg.substring('--test-randomize-ordering-seed='.length);
         removeArgs.add(arg);
       }
+      if (arg == '--no-smoke-tests') {
+        runSmokeTests = false;
+        removeArgs.add(arg);
+      }
     }
     flutterTestArgs.removeWhere((String arg) => removeArgs.contains(arg));
     if (Platform.environment.containsKey(CIRRUS_TASK_NAME))
       print('Running task: ${Platform.environment[CIRRUS_TASK_NAME]}');
     print('═' * 80);
-    await _runSmokeTests();
+    if (runSmokeTests) {
+      await _runSmokeTests();
+    }
     print('═' * 80);
     await selectShard(<String, ShardRunner>{
       'add_to_app_life_cycle_tests': _runAddToAppLifeCycleTests,
@@ -474,7 +481,7 @@ Future<void> _runBuildTests() async {
 Future<void> _runExampleProjectBuildTests(Directory exampleDirectory, [File? mainFile]) async {
   // Only verify caching with flutter gallery.
   final bool verifyCaching = exampleDirectory.path.contains('flutter_gallery');
-  final String examplePath = exampleDirectory.path;
+  final String examplePath = path.relative(exampleDirectory.path, from: Directory.current.path);
   final bool hasNullSafety = File(path.join(examplePath, 'null_safety')).existsSync();
   final List<String> additionalArgs = <String>[
     if (hasNullSafety) '--no-sound-null-safety',
@@ -786,7 +793,8 @@ Future<void> _runFrameworkTests() async {
     await _pubRunTest(path.join(flutterRoot, 'dev', 'bots'));
     await _pubRunTest(path.join(flutterRoot, 'dev', 'devicelab'), ensurePrecompiledTool: false); // See https://github.com/flutter/flutter/issues/86209
     await _pubRunTest(path.join(flutterRoot, 'dev', 'conductor', 'core'), forceSingleCore: true);
-    await _runFlutterTest(path.join(flutterRoot, 'dev', 'integration_tests', 'android_semantics_testing'));
+    // TODO(gspencergoog): Remove the exception for fatalWarnings once https://github.com/flutter/flutter/pull/91127 has landed.
+    await _runFlutterTest(path.join(flutterRoot, 'dev', 'integration_tests', 'android_semantics_testing'), fatalWarnings: false);
     await _runFlutterTest(path.join(flutterRoot, 'dev', 'manual_tests'));
     await _runFlutterTest(path.join(flutterRoot, 'dev', 'tools', 'vitool'));
     await _runFlutterTest(path.join(flutterRoot, 'dev', 'tools', 'gen_keycodes'));
@@ -1621,6 +1629,7 @@ Future<void> _runFlutterTest(String workingDirectory, {
   Map<String, String>? environment,
   List<String> tests = const <String>[],
   bool shuffleTests = true,
+  bool fatalWarnings = true,
 }) async {
   assert(!printOutput || outputChecker == null, 'Output either can be printed or checked but not both');
 
@@ -1634,6 +1643,7 @@ Future<void> _runFlutterTest(String workingDirectory, {
   final List<String> args = <String>[
     'test',
     if (shuffleTests) '--test-randomize-ordering-seed=$shuffleSeed',
+    if (fatalWarnings) '--fatal-warnings',
     ...options,
     ...tags,
     ...flutterTestArgs,

dev/conductor/core/lib/src/codesign.dart

@@ -43,15 +43,13 @@ class CodesignCommand extends Command<void> {
     }
     argParser.addFlag(
       kVerify,
-      help:
+      help: 'Only verify expected binaries exist and are codesigned with entitlements.',
-          'Only verify expected binaries exist and are codesigned with entitlements.',
     );
     argParser.addFlag(
       kSignatures,
       defaultsTo: true,
-      help:
+      help: 'When off, this command will only verify the existence of binaries, and not their\n'
-          'When off, this command will only verify the existence of binaries, and not their\n'
+            'signatures or entitlements. Must be used with --verify flag.',
-          'signatures or entitlements. Must be used with --verify flag.',
     );
     argParser.addOption(
       kUpstream,
@@ -92,24 +90,25 @@ class CodesignCommand extends Command<void> {
   Future<void> run() async {
     if (!platform.isMacOS) {
       throw ConductorException(
-          'Error! Expected operating system "macos", actual operating system is: '
+        'Error! Expected operating system "macos", actual operating system is: '
-          '"${platform.operatingSystem}"');
+        '"${platform.operatingSystem}"',
+      );
     }
 
     if (argResults!['verify'] as bool != true) {
       throw ConductorException(
-          'Sorry, but codesigning is not implemented yet. Please pass the '
+        'Sorry, but codesigning is not implemented yet. Please pass the '
-          '--$kVerify flag to verify signatures.');
+        '--$kVerify flag to verify signatures.',
+      );
     }
 
     String revision;
     if (argResults!.wasParsed(kRevision)) {
-      stdio.printError(
+      stdio.printWarning(
-          'Warning! When providing an arbitrary revision, the contents of the cache may not');
+        'Warning! When providing an arbitrary revision, the contents of the cache may not '
-      stdio.printError(
+        'match the expected binaries in the conductor tool. It is preferred to check out '
-          'match the expected binaries in the conductor tool. It is preferred to check out');
+        'the desired revision and run that version of the conductor.\n',
-      stdio.printError(
+      );
-          'the desired revision and run that version of the conductor.\n');
       revision = argResults![kRevision] as String;
     } else {
       revision = ((await processManager.run(
@@ -225,13 +224,11 @@ class CodesignCommand extends Command<void> {
           )
           .toList();
       stdio.printError(
-          'Expected binaries not found in cache:\n\n${unfoundFiles.join('\n')}\n');
+        'Expected binaries not found in cache:\n\n${unfoundFiles.join('\n')}\n\n'
-      stdio.printError(
+        'If this commit is removing binaries from the cache, this test should be fixed by\n'
-          'If this commit is removing binaries from the cache, this test should be fixed by');
+        'removing the relevant entry from either the "binariesWithEntitlements" or\n'
-      stdio.printError(
+        '"binariesWithoutEntitlements" getters in dev/tools/lib/codesign.dart.',
-          'removing the relevant entry from either the `binariesWithEntitlements` or');
+      );
-      stdio.printError(
-          '`binariesWithoutEntitlements` getters in dev/tools/lib/codesign.dart.');
       throw ConductorException('Did not find all expected binaries!');
     }
 
@@ -271,9 +268,10 @@ class CodesignCommand extends Command<void> {
       if (codeSignResult.exitCode != 0) {
         unsignedBinaries.add(binaryPath);
         stdio.printError(
-            'File "$binaryPath" does not appear to be codesigned.\n'
+          'File "$binaryPath" does not appear to be codesigned.\n'
-            'The `codesign` command failed with exit code ${codeSignResult.exitCode}:\n'
+          'The `codesign` command failed with exit code ${codeSignResult.exitCode}:\n'
-            '${codeSignResult.stderr}\n');
+          '${codeSignResult.stderr}\n',
+        );
         continue;
       }
       if (verifyEntitlements) {
@@ -291,42 +289,39 @@ class CodesignCommand extends Command<void> {
     }
 
     if (wrongEntitlementBinaries.isNotEmpty) {
-      stdio.printError(
+      stdio.printError('Found ${wrongEntitlementBinaries.length} binaries with unexpected entitlements:');
-          'Found ${wrongEntitlementBinaries.length} binaries with unexpected entitlements:');
       wrongEntitlementBinaries.forEach(stdio.printError);
     }
 
     if (unexpectedBinaries.isNotEmpty) {
-      stdio.printError(
+      stdio.printError('Found ${unexpectedBinaries.length} unexpected binaries in the cache:');
-          'Found ${unexpectedBinaries.length} unexpected binaries in the cache:');
       unexpectedBinaries.forEach(print);
     }
 
     // Finally, exit on any invalid state
     if (unsignedBinaries.isNotEmpty) {
-      throw ConductorException(
+      throw ConductorException('Test failed because unsigned binaries detected.');
-          'Test failed because unsigned binaries detected.');
     }
 
     if (wrongEntitlementBinaries.isNotEmpty) {
       throw ConductorException(
-          'Test failed because files found with the wrong entitlements:\n'
+        'Test failed because files found with the wrong entitlements:\n'
-          '${wrongEntitlementBinaries.join('\n')}');
+        '${wrongEntitlementBinaries.join('\n')}',
+      );
     }
 
     if (unexpectedBinaries.isNotEmpty) {
-      throw ConductorException(
+      throw ConductorException('Test failed because unexpected binaries found in the cache.');
-          'Test failed because unexpected binaries found in the cache.');
     }
 
     final String? desiredRevision = argResults![kRevision] as String?;
     if (desiredRevision == null) {
-      stdio.printStatus(
+      stdio.printStatus('Verified that binaries are codesigned and have expected entitlements.');
-          'Verified that binaries are codesigned and have expected entitlements.');
     } else {
       stdio.printStatus(
-          'Verified that binaries for commit $desiredRevision are codesigned and have '
+        'Verified that binaries for commit $desiredRevision are codesigned and have '
-          'expected entitlements.');
+        'expected entitlements.',
+      );
     }
   }
 
@@ -387,8 +382,9 @@ class CodesignCommand extends Command<void> {
 
     if (entitlementResult.exitCode != 0) {
       stdio.printError(
-          'The `codesign --entitlements` command failed with exit code ${entitlementResult.exitCode}:\n'
+        'The `codesign --entitlements` command failed with exit code ${entitlementResult.exitCode}:\n'
-          '${entitlementResult.stderr}\n');
+        '${entitlementResult.stderr}\n',
+      );
       return false;
     }
 
@@ -399,8 +395,9 @@ class CodesignCommand extends Command<void> {
           (await binariesWithEntitlements).contains(binaryPath);
       if (output.contains(entitlement) != entitlementExpected) {
         stdio.printError(
-            'File "$binaryPath" ${entitlementExpected ? 'does not have expected' : 'has unexpected'} '
+          'File "$binaryPath" ${entitlementExpected ? 'does not have expected' : 'has unexpected'} '
-            'entitlement $entitlement.');
+          'entitlement $entitlement.',
+        );
         passes = false;
       }
     }

dev/conductor/core/lib/src/stdio.dart

@@ -9,25 +9,44 @@ import 'package:meta/meta.dart';
 abstract class Stdio {
   final List<String> logs = <String>[];
 
-  /// Error/warning messages printed to STDERR.
+  /// Error messages printed to STDERR.
+  ///
+  /// Display an error `message` to the user on stderr. Print errors if the code
+  /// fails in some way. Errors are typically followed shortly by exiting the
+  /// app with a non-zero exit status.
   @mustCallSuper
   void printError(String message) {
     logs.add('[error] $message');
   }
 
+  /// Warning messages printed to STDERR.
+  ///
+  /// Display a warning `message` to the user on stderr. Print warnings if there
+  /// is important information to convey to the user that is not fatal.
+  @mustCallSuper
+  void printWarning(String message) {
+    logs.add('[warning] $message');
+  }
+
   /// Ordinary STDOUT messages.
+  ///
+  /// Displays normal output on stdout. This should be used for things like
+  /// progress messages, success messages, or just normal command output.
   @mustCallSuper
   void printStatus(String message) {
     logs.add('[status] $message');
   }
 
   /// Debug messages that are only printed in verbose mode.
+  ///
+  /// Use this for verbose tracing output. Users can turn this output on in order
+  /// to help diagnose issues.
   @mustCallSuper
   void printTrace(String message) {
     logs.add('[trace] $message');
   }
 
-  /// Write string to STDOUT without trailing newline.
+  /// Write the `message` string to STDOUT without a trailing newline.
   @mustCallSuper
   void write(String message) {
     logs.add('[write] $message');

dev/devicelab/lib/command/test.dart

@@ -49,6 +49,7 @@ class TestCommand extends Command<void> {
             'task, will write test results to the file.');
     argParser.addFlag(
       'silent',
+      help: 'Suppresses standard output and only print standard error output.',
     );
   }
 

packages/flutter_tools/bin/fuchsia_asset_builder.dart

@@ -6,6 +6,7 @@
 
 import 'package:args/args.dart';
 import 'package:flutter_tools/src/asset.dart' hide defaultManifestPath;
+import 'package:flutter_tools/src/base/common.dart';
 import 'package:flutter_tools/src/base/context.dart';
 import 'package:flutter_tools/src/base/file_system.dart' as libfs;
 import 'package:flutter_tools/src/base/io.dart';
@@ -70,8 +71,7 @@ Future<void> run(List<String> args) async {
   );
 
   if (assets == null) {
-    print('Unable to find assets.');
+    throwToolExit('Unable to find assets.', exitCode: 1);
-    exit(1);
   }
 
   final List<Future<void>> calls = <Future<void>>[];

packages/flutter_tools/lib/runner.dart

@@ -39,7 +39,7 @@ Future<int> run(
     // Remove the verbose option; for help and doctor, users don't need to see
     // verbose logs.
     args = List<String>.of(args);
-    args.removeWhere((String option) => option == '-v' || option == '--verbose');
+    args.removeWhere((String option) => option == '-vv' || option == '-v' || option == '--verbose');
   }
 
   return runInContext<int>(() async {

packages/flutter_tools/lib/src/base/logger.dart

@@ -7,6 +7,7 @@ import 'dart:async';
 import 'package:meta/meta.dart';
 
 import '../convert.dart';
+import 'common.dart';
 import 'io.dart';
 import 'terminal.dart' show Terminal, TerminalColor, OutputPreferences;
 import 'utils.dart';
@@ -28,22 +29,41 @@ class StopwatchFactory {
 typedef VoidCallback = void Function();
 
 abstract class Logger {
+  /// Whether or not this logger should print [printTrace] messages.
   bool get isVerbose => false;
 
+  /// If true, silences the logger output.
   bool quiet = false;
 
+  /// If true, this logger supports color output.
   bool get supportsColor;
 
+  /// If true, this logger is connected to a terminal.
   bool get hasTerminal;
 
+  /// If true, then [printError] has been called at least once for this logger
+  /// since the last time it was set to false.
+  bool hadErrorOutput = false;
+
+  /// If true, then [printWarning] has been called at least once for this logger
+  /// since the last time it was reset to false.
+  bool hadWarningOutput = false;
+
+  /// Causes [checkForFatalLogs] to call [throwToolExit] when it is called if
+  /// [hadWarningOutput] is true.
+  bool fatalWarnings = false;
+
+  /// Returns the terminal attached to this logger.
   Terminal get terminal;
 
   OutputPreferences get _outputPreferences;
 
   /// Display an error `message` to the user. Commands should use this if they
-  /// fail in some way.
+  /// fail in some way. Errors are typically followed shortly by a call to
+  /// [throwToolExit] to terminate the run.
   ///
-  /// The `message` argument is printed to the stderr in red by default.
+  /// The `message` argument is printed to the stderr in [TerminalColor.red] by
+  /// default.
   ///
   /// The `stackTrace` argument is the stack trace that will be printed if
   /// supplied.
@@ -74,10 +94,41 @@ abstract class Logger {
     bool? wrap,
   });
 
+  /// Display a warning `message` to the user. Commands should use this if they
+  /// important information to convey to the user that is not fatal.
+  ///
+  /// The `message` argument is printed to the stderr in [TerminalColor.cyan] by
+  /// default.
+  ///
+  /// The `emphasis` argument will cause the output message be printed in bold text.
+  ///
+  /// The `color` argument will print the message in the supplied color instead
+  /// of the default of cyan. Colors will not be printed if the output terminal
+  /// doesn't support them.
+  ///
+  /// The `indent` argument specifies the number of spaces to indent the overall
+  /// message. If wrapping is enabled in [outputPreferences], then the wrapped
+  /// lines will be indented as well.
+  ///
+  /// If `hangingIndent` is specified, then any wrapped lines will be indented
+  /// by this much more than the first line, if wrapping is enabled in
+  /// [outputPreferences].
+  ///
+  /// If `wrap` is specified, then it overrides the
+  /// `outputPreferences.wrapText` setting.
+  void printWarning(
+    String message, {
+    bool? emphasis,
+    TerminalColor? color,
+    int? indent,
+    int? hangingIndent,
+    bool? wrap,
+  });
+
   /// Display normal output of the command. This should be used for things like
   /// progress messages, success messages, or just normal command output.
   ///
-  /// The `message` argument is printed to the stderr in red by default.
+  /// The `message` argument is printed to the stdout.
   ///
   /// The `stackTrace` argument is the stack trace that will be printed if
   /// supplied.
@@ -144,9 +195,21 @@ abstract class Logger {
 
   /// Clears all output.
   void clear();
+
+  /// If [fatalWarnings] is set, causes the logger to check if
+  /// [hadWarningOutput] is true, and then to call [throwToolExit] if so.
+  ///
+  /// The [fatalWarnings] flag can be set from the command line with the
+  /// "--fatal-warnings" option on commands that support it.
+  void checkForFatalLogs() {
+    if (fatalWarnings && (hadWarningOutput || hadErrorOutput)) {
+      throwToolExit('Logger received ${hadErrorOutput ? 'error' : 'warning'} output '
+          'during the run, and "--fatal-warnings" is enabled.');
+    }
+  }
 }
 
-/// A [Logger] that forwards all methods to another one.
+/// A [Logger] that forwards all methods to another logger.
 ///
 /// Classes can derive from this to add functionality to an existing [Logger].
 class DelegatingLogger implements Logger {
@@ -174,6 +237,24 @@ class DelegatingLogger implements Logger {
   @override
   bool get isVerbose => _delegate.isVerbose;
 
+  @override
+  bool get hadErrorOutput => _delegate.hadErrorOutput;
+
+  @override
+  set hadErrorOutput(bool value) => _delegate.hadErrorOutput = value;
+
+  @override
+  bool get hadWarningOutput => _delegate.hadWarningOutput;
+
+  @override
+  set hadWarningOutput(bool value) => _delegate.hadWarningOutput = value;
+
+  @override
+  bool get fatalWarnings => _delegate.fatalWarnings;
+
+  @override
+  set fatalWarnings(bool value) => _delegate.fatalWarnings = value;
+
   @override
   void printError(String message, {
     StackTrace? stackTrace,
@@ -194,6 +275,24 @@ class DelegatingLogger implements Logger {
     );
   }
 
+  @override
+  void printWarning(String message, {
+    bool? emphasis,
+    TerminalColor? color,
+    int? indent,
+    int? hangingIndent,
+    bool? wrap,
+  }) {
+    _delegate.printWarning(
+      message,
+      emphasis: emphasis,
+      color: color,
+      indent: indent,
+      hangingIndent: hangingIndent,
+      wrap: wrap,
+    );
+  }
+
   @override
   void printStatus(String message, {
     bool? emphasis,
@@ -244,6 +343,9 @@ class DelegatingLogger implements Logger {
 
   @override
   void clear() => _delegate.clear();
+
+  @override
+  void checkForFatalLogs() => _delegate.checkForFatalLogs();
 }
 
 /// If [logger] is a [DelegatingLogger], walks the delegate chain and returns
@@ -303,6 +405,7 @@ class StdoutLogger extends Logger {
     int? hangingIndent,
     bool? wrap,
   }) {
+    hadErrorOutput = true;
     _status?.pause();
     message = wrapText(message,
       indent: indent,
@@ -321,6 +424,31 @@ class StdoutLogger extends Logger {
     _status?.resume();
   }
 
+  @override
+  void printWarning(
+    String message, {
+    bool? emphasis,
+    TerminalColor? color,
+    int? indent,
+    int? hangingIndent,
+    bool? wrap,
+  }) {
+    hadWarningOutput = true;
+    _status?.pause();
+    message = wrapText(message,
+      indent: indent,
+      hangingIndent: hangingIndent,
+      shouldWrap: wrap ?? _outputPreferences.wrapText,
+      columnWidth: _outputPreferences.wrapColumn,
+    );
+    if (emphasis == true) {
+      message = terminal.bolden(message);
+    }
+    message = terminal.color(message, color ?? TerminalColor.cyan);
+    writeToStdErr('$message\n');
+    _status?.resume();
+  }
+
   @override
   void printStatus(
     String message, {
@@ -482,7 +610,6 @@ class BufferLogger extends Logger {
        _outputPreferences = outputPreferences ?? OutputPreferences.test(),
        _stopwatchFactory = const StopwatchFactory();
 
-
   @override
   final OutputPreferences _outputPreferences;
 
@@ -498,11 +625,13 @@ class BufferLogger extends Logger {
   bool get supportsColor => terminal.supportsColor;
 
   final StringBuffer _error = StringBuffer();
+  final StringBuffer _warning = StringBuffer();
   final StringBuffer _status = StringBuffer();
   final StringBuffer _trace = StringBuffer();
   final StringBuffer _events = StringBuffer();
 
   String get errorText => _error.toString();
+  String get warningText => _warning.toString();
   String get statusText => _status.toString();
   String get traceText => _trace.toString();
   String get eventText => _events.toString();
@@ -520,6 +649,7 @@ class BufferLogger extends Logger {
     int? hangingIndent,
     bool? wrap,
   }) {
+    hadErrorOutput = true;
     _error.writeln(terminal.color(
       wrapText(message,
         indent: indent,
@@ -531,6 +661,27 @@ class BufferLogger extends Logger {
     ));
   }
 
+  @override
+  void printWarning(
+    String message, {
+    bool? emphasis,
+    TerminalColor? color,
+    int? indent,
+    int? hangingIndent,
+    bool? wrap,
+  }) {
+    hadWarningOutput = true;
+    _warning.writeln(terminal.color(
+      wrapText(message,
+        indent: indent,
+        hangingIndent: hangingIndent,
+        shouldWrap: wrap ?? _outputPreferences.wrapText,
+        columnWidth: _outputPreferences.wrapColumn,
+      ),
+      color ?? TerminalColor.cyan,
+    ));
+  }
+
   @override
   void printStatus(
     String message, {
@@ -625,6 +776,7 @@ class VerboseLogger extends DelegatingLogger {
     int? hangingIndent,
     bool? wrap,
   }) {
+    hadErrorOutput = true;
     _emit(
       _LogType.error,
       wrapText(message,
@@ -637,6 +789,29 @@ class VerboseLogger extends DelegatingLogger {
     );
   }
 
+  @override
+  void printWarning(
+      String message, {
+        StackTrace? stackTrace,
+        bool? emphasis,
+        TerminalColor? color,
+        int? indent,
+        int? hangingIndent,
+        bool? wrap,
+      }) {
+    hadWarningOutput = true;
+    _emit(
+      _LogType.warning,
+      wrapText(message,
+        indent: indent,
+        hangingIndent: hangingIndent,
+        shouldWrap: wrap ?? _outputPreferences.wrapText,
+        columnWidth: _outputPreferences.wrapColumn,
+      ),
+      stackTrace,
+    );
+  }
+
   @override
   void printStatus(
     String message, {
@@ -707,15 +882,25 @@ class VerboseLogger extends DelegatingLogger {
     final String indent = ''.padLeft(prefix.length);
     final String indentMessage = message.replaceAll('\n', '\n$indent');
 
-    if (type == _LogType.error) {
+    switch (type) {
-      super.printError(prefix + terminal.bolden(indentMessage));
+      case _LogType.error:
-      if (stackTrace != null) {
+        super.printError(prefix + terminal.bolden(indentMessage));
-        super.printError(indent + stackTrace.toString().replaceAll('\n', '\n$indent'));
+        if (stackTrace != null) {
-      }
+          super.printError(indent + stackTrace.toString().replaceAll('\n', '\n$indent'));
-    } else if (type == _LogType.status) {
+        }
-      super.printStatus(prefix + terminal.bolden(indentMessage));
+        break;
-    } else {
+      case _LogType.warning:
-      super.printStatus(prefix + indentMessage);
+        super.printWarning(prefix + terminal.bolden(indentMessage));
+        break;
+      case _LogType.status:
+        super.printStatus(prefix + terminal.bolden(indentMessage));
+        break;
+      case _LogType.trace:
+        // This seems wrong, since there is a 'printTrace' to call on the
+        // superclass, but it's actually the entire point of this logger: to
+        // make things more verbose than they normally would be.
+        super.printStatus(prefix + indentMessage);
+        break;
     }
   }
 
@@ -736,6 +921,7 @@ class PrefixedErrorLogger extends DelegatingLogger {
     int? hangingIndent,
     bool? wrap,
   }) {
+    hadErrorOutput = true;
     if (message.trim().isNotEmpty == true) {
       message = 'ERROR: $message';
     }
@@ -751,7 +937,7 @@ class PrefixedErrorLogger extends DelegatingLogger {
   }
 }
 
-enum _LogType { error, status, trace }
+enum _LogType { error, warning, status, trace }
 
 typedef SlowWarningCallback = String Function();
 
@@ -820,7 +1006,7 @@ abstract class Status {
   }
 }
 
-/// A [SilentStatus] shows nothing.
+/// A [Status] that shows nothing.
 class SilentStatus extends Status {
   SilentStatus({
     required Stopwatch stopwatch,

packages/flutter_tools/lib/src/build_info.dart

@@ -751,7 +751,7 @@ HostPlatform getCurrentHostPlatform() {
     return HostPlatform.windows_x64;
   }
 
-  globals.printError('Unsupported host platform, defaulting to Linux');
+  globals.printWarning('Unsupported host platform, defaulting to Linux');
 
   return HostPlatform.linux_x64;
 }

packages/flutter_tools/lib/src/build_system/targets/web.dart

@@ -266,7 +266,7 @@ class Dart2JSTarget extends Target {
     final File dart2jsDeps = environment.buildDir
       .childFile('app.dill.deps');
     if (!dart2jsDeps.existsSync()) {
-      globals.printError('Warning: dart2js did not produced expected deps list at '
+      globals.printWarning('Warning: dart2js did not produced expected deps list at '
         '${dart2jsDeps.path}');
       return;
     }

packages/flutter_tools/lib/src/bundle_builder.dart

@@ -140,7 +140,7 @@ Future<void> writeBundle(
     try {
       bundleDir.deleteSync(recursive: true);
     } on FileSystemException catch (err) {
-      loggerOverride.printError(
+      loggerOverride.printWarning(
         'Failed to clean up asset directory ${bundleDir.path}: $err\n'
         'To clean build artifacts, use the command "flutter clean".'
       );

packages/flutter_tools/lib/src/cache.dart

@@ -164,6 +164,7 @@ class Cache {
 
   late final ArtifactUpdater _artifactUpdater = _createUpdater();
 
+  @visibleForTesting
   @protected
   void registerArtifact(ArtifactSet artifactSet) {
     _artifacts.add(artifactSet);
@@ -320,13 +321,17 @@ class Cache {
       } on FileSystemException {
         if (!printed) {
           _logger.printTrace('Waiting to be able to obtain lock of Flutter binary artifacts directory: ${_lock!.path}');
-          // This needs to go to stderr to avoid cluttering up stdout if a parent
+          // This needs to go to stderr to avoid cluttering up stdout if a
-          // process is collecting stdout. It's not really an "error" though,
+          // parent process is collecting stdout (e.g. when calling "flutter
-          // so print it in grey.
+          // version --machine"). It's not really a "warning" though, so print it
-          _logger.printError(
+          // in grey. Also, make sure that it isn't counted as a warning for
+          // Logger.warningsAreFatal.
+          final bool oldWarnings = _logger.hadWarningOutput;
+          _logger.printWarning(
             'Waiting for another flutter command to release the startup lock...',
             color: TerminalColor.grey,
           );
+          _logger.hadWarningOutput = oldWarnings;
           printed = true;
         }
         await Future<void>.delayed(const Duration(milliseconds: 50));
@@ -509,7 +514,7 @@ class Cache {
         ErrorHandlingFileSystem.deleteIfExists(file);
       }
     } on FileSystemException catch (err) {
-      _logger.printError('Failed to delete some stamp files: $err');
+      _logger.printWarning('Failed to delete some stamp files: $err');
     }
   }
 
@@ -703,7 +708,7 @@ abstract class CachedArtifact extends ArtifactSet {
     await updateInner(artifactUpdater, fileSystem, operatingSystemUtils);
     try {
       if (version == null) {
-        logger.printError(
+        logger.printWarning(
           'No known version for the artifact name "$name". '
           'Flutter can continue, but the artifact may be re-downloaded on '
           'subsequent invocations until the problem is resolved.',
@@ -712,7 +717,7 @@ abstract class CachedArtifact extends ArtifactSet {
         cache.setStampFor(stampName, version!);
       }
     } on FileSystemException catch (err) {
-      logger.printError(
+      logger.printWarning(
         'The new artifact "$name" was downloaded, but Flutter failed to update '
         'its stamp file, receiving the error "$err". '
         'Flutter can continue, but the artifact may be re-downloaded on '
@@ -1103,7 +1108,7 @@ class ArtifactUpdater {
       try {
         file.deleteSync();
       } on FileSystemException catch (e) {
-        _logger.printError('Failed to delete "${file.path}". Please delete manually. $e');
+        _logger.printWarning('Failed to delete "${file.path}". Please delete manually. $e');
         continue;
       }
       for (Directory directory = file.parent; directory.absolute.path != _tempStorage.absolute.path; directory = directory.parent) {

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

@@ -65,8 +65,9 @@ class BuildCommand extends FlutterCommand {
 }
 
 abstract class BuildSubCommand extends FlutterCommand {
-  BuildSubCommand() {
+  BuildSubCommand({@required bool verboseHelp}) {
     requiresPubspecYaml();
+    usesFatalWarningsOption(verboseHelp: verboseHelp);
   }
 
   @override

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

@@ -20,7 +20,7 @@ import '../runner/flutter_command.dart' show FlutterCommandResult;
 import 'build.dart';
 
 class BuildAarCommand extends BuildSubCommand {
-  BuildAarCommand({ @required bool verboseHelp }) {
+  BuildAarCommand({ @required bool verboseHelp }) : super(verboseHelp: verboseHelp) {
     argParser
       ..addFlag(
         'debug',

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

@@ -16,7 +16,7 @@ import '../runner/flutter_command.dart' show FlutterCommandResult;
 import 'build.dart';
 
 class BuildApkCommand extends BuildSubCommand {
-  BuildApkCommand({bool verboseHelp = false}) {
+  BuildApkCommand({bool verboseHelp = false}) : super(verboseHelp: verboseHelp) {
     addTreeShakeIconsFlag();
     usesTargetOption();
     addBuildModeFlags(verboseHelp: verboseHelp);

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

@@ -19,7 +19,9 @@ import '../runner/flutter_command.dart' show FlutterCommandResult;
 import 'build.dart';
 
 class BuildAppBundleCommand extends BuildSubCommand {
-  BuildAppBundleCommand({bool verboseHelp = false}) {
+  BuildAppBundleCommand({
+    bool verboseHelp = false,
+  }) : super(verboseHelp: verboseHelp) {
     addTreeShakeIconsFlag();
     usesTargetOption();
     addBuildModeFlags(verboseHelp: verboseHelp);

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

@@ -16,7 +16,10 @@ import '../runner/flutter_command.dart';
 import 'build.dart';
 
 class BuildBundleCommand extends BuildSubCommand {
-  BuildBundleCommand({bool verboseHelp = false, this.bundleBuilder}) {
+  BuildBundleCommand({
+    bool verboseHelp = false,
+    this.bundleBuilder,
+  }) : super(verboseHelp: verboseHelp) {
     usesTargetOption();
     usesFilesystemOptions(hide: !verboseHelp);
     usesBuildNumberOption();

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

@@ -19,7 +19,9 @@ import 'build.dart';
 
 /// A command to build a Fuchsia target.
 class BuildFuchsiaCommand extends BuildSubCommand {
-  BuildFuchsiaCommand({ @required bool verboseHelp }) {
+  BuildFuchsiaCommand({
+    @required bool verboseHelp,
+  }) : super(verboseHelp: verboseHelp) {
     addTreeShakeIconsFlag();
     usesTargetOption();
     usesDartDefineOption();

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

@@ -129,7 +129,7 @@ class BuildIOSArchiveCommand extends _BuildIOSSubCommand {
 
     // xcarchive failed or not at expected location.
     if (xcarchiveResult.exitStatus != ExitStatus.success) {
-      globals.logger.printStatus('Skipping IPA');
+      globals.printStatus('Skipping IPA');
       return xcarchiveResult;
     }
 
@@ -176,14 +176,16 @@ class BuildIOSArchiveCommand extends _BuildIOSSubCommand {
       throwToolExit('Encountered error while building IPA:\n$errorMessage');
     }
 
-    globals.logger.printStatus('Built IPA to $outputPath.');
+    globals.printStatus('Built IPA to $outputPath.');
 
     return FlutterCommandResult.success();
   }
 }
 
 abstract class _BuildIOSSubCommand extends BuildSubCommand {
-  _BuildIOSSubCommand({ @required bool verboseHelp }) {
+  _BuildIOSSubCommand({
+    @required bool verboseHelp
+  }) : super(verboseHelp: verboseHelp) {
     addTreeShakeIconsFlag();
     addSplitDebugInfoOption();
     addBuildModeFlags(verboseHelp: verboseHelp);

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

@@ -39,7 +39,8 @@ class BuildIOSFrameworkCommand extends BuildSubCommand {
   }) : _flutterVersion = flutterVersion,
        _buildSystem = buildSystem,
        _injectedCache = cache,
-       _injectedPlatform = platform {
+       _injectedPlatform = platform,
+       super(verboseHelp: verboseHelp) {
     addTreeShakeIconsFlag();
     usesTargetOption();
     usesFlavorOption();

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

@@ -23,7 +23,8 @@ class BuildLinuxCommand extends BuildSubCommand {
   BuildLinuxCommand({
     @required OperatingSystemUtils operatingSystemUtils,
     bool verboseHelp = false,
-  }) : _operatingSystemUtils = operatingSystemUtils {
+  }) : _operatingSystemUtils = operatingSystemUtils,
+       super(verboseHelp: verboseHelp) {
     addCommonDesktopBuildOptions(verboseHelp: verboseHelp);
     final String defaultTargetPlatform =
         (_operatingSystemUtils.hostPlatform == HostPlatform.linux_arm64) ?

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

@@ -19,7 +19,9 @@ import 'build.dart';
 
 /// A command to build a macOS desktop target through a build shell script.
 class BuildMacosCommand extends BuildSubCommand {
-  BuildMacosCommand({ @required bool verboseHelp }) {
+  BuildMacosCommand({
+    @required bool verboseHelp,
+  }) : super(verboseHelp: verboseHelp) {
     addCommonDesktopBuildOptions(verboseHelp: verboseHelp);
     usesBuildNumberOption();
     usesBuildNameOption();

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

@@ -20,7 +20,7 @@ import 'build.dart';
 class BuildWebCommand extends BuildSubCommand {
   BuildWebCommand({
     @required bool verboseHelp,
-  }) {
+  }) : super(verboseHelp: verboseHelp) {
     addTreeShakeIconsFlag(enabledByDefault: false);
     usesTargetOption();
     usesPubOption();

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

@@ -20,7 +20,9 @@ import 'build.dart';
 
 /// A command to build a windows desktop target through a build shell script.
 class BuildWindowsCommand extends BuildSubCommand {
-  BuildWindowsCommand({ bool verboseHelp = false }) {
+  BuildWindowsCommand({
+    bool verboseHelp = false,
+  }) : super(verboseHelp: verboseHelp) {
     addCommonDesktopBuildOptions(verboseHelp: verboseHelp);
   }
 

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

@@ -19,7 +19,9 @@ import 'build.dart';
 
 /// A command to build a Windows UWP desktop target.
 class BuildWindowsUwpCommand extends BuildSubCommand {
-  BuildWindowsUwpCommand({ bool verboseHelp = false }) {
+  BuildWindowsUwpCommand({
+    bool verboseHelp = false,
+  }) : super(verboseHelp: verboseHelp) {
     addCommonDesktopBuildOptions(verboseHelp: verboseHelp);
   }
 

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

@@ -228,7 +228,7 @@ class CreateCommand extends CreateBase {
     validateProjectDir(overwrite: overwrite);
 
     if (boolArg('with-driver-test')) {
-      globals.printError(
+      globals.printWarning(
         'The "--with-driver-test" argument has been deprecated and will no longer add a flutter '
         'driver template. Instead, learn how to use package:integration_test by '
         'visiting https://pub.dev/packages/integration_test .'

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

@@ -309,7 +309,7 @@ class DaemonDomain extends Domain {
           // capture the print output for testing.
           // ignore: avoid_print
           print(message.message);
-        } else if (message.level == 'error') {
+        } else if (message.level == 'error' || message.level == 'warning') {
           globals.stdio.stderrWrite('${message.message}\n');
           if (message.stackTrace != null) {
             globals.stdio.stderrWrite(
@@ -1011,6 +1011,18 @@ class NotifyingLogger extends DelegatingLogger {
     _sendMessage(LogMessage('error', message, stackTrace));
   }
 
+  @override
+  void printWarning(
+    String message, {
+    bool emphasis = false,
+    TerminalColor color,
+    int indent,
+    int hangingIndent,
+    bool wrap,
+  }) {
+    _sendMessage(LogMessage('warning', message));
+  }
+
   @override
   void printStatus(
     String message, {

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

@@ -48,7 +48,7 @@ class DevicesCommand extends FlutterCommand {
   @override
   Future<void> validateCommand() {
     if (argResults?['timeout'] != null) {
-      globals.printError('${globals.logger.terminal.warningMark} The "--timeout" argument is deprecated; use "--${FlutterOptions.kDeviceTimeout}" instead.');
+      globals.printWarning('${globals.logger.terminal.warningMark} The "--timeout" argument is deprecated; use "--${FlutterOptions.kDeviceTimeout}" instead.');
     }
     return super.validateCommand();
   }

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

@@ -98,7 +98,7 @@ Future<bool> installApp(
     if (uninstall && await device.isAppInstalled(package, userIdentifier: userIdentifier)) {
       globals.printStatus('Uninstalling old version...');
       if (!await device.uninstallApp(package, userIdentifier: userIdentifier)) {
-        globals.printError('Warning: uninstalling old version failed');
+        globals.printWarning('Warning: uninstalling old version failed');
       }
     }
   } on ProcessException catch (e) {

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

@@ -153,6 +153,7 @@ abstract class RunCommandBase extends FlutterCommand with DeviceBasedDevelopment
     addDdsOptions(verboseHelp: verboseHelp);
     addDevToolsOptions(verboseHelp: verboseHelp);
     addAndroidSpecificBuildOptions(hide: !verboseHelp);
+    usesFatalWarningsOption(verboseHelp: verboseHelp);
   }
 
   bool get traceStartup => boolArg('trace-startup');

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

@@ -216,7 +216,8 @@ class TestCommand extends FlutterCommand with DeviceBasedDevelopmentArtifacts {
               'or as the string "none" to disable the timeout entirely.',
         defaultsTo: '30s',
       );
-      addDdsOptions(verboseHelp: verboseHelp);
+    addDdsOptions(verboseHelp: verboseHelp);
+    usesFatalWarningsOption(verboseHelp: verboseHelp);
   }
 
   /// The interface for starting and configuring the tester.
@@ -283,7 +284,7 @@ class TestCommand extends FlutterCommand with DeviceBasedDevelopmentArtifacts {
     // correct [requiredArtifacts] can be identified before [run] takes place.
     _isIntegrationTest = _shouldRunAsIntegrationTests(globals.fs.currentDirectory.absolute.path, _testFiles);
 
-    globals.logger.printTrace(
+    globals.printTrace(
       'Found ${_testFiles.length} files which will be executed as '
       '${_isIntegrationTest ? 'Integration' : 'Widget'} Tests.',
     );
@@ -338,7 +339,7 @@ class TestCommand extends FlutterCommand with DeviceBasedDevelopmentArtifacts {
     }
     if (_isIntegrationTest) {
       if (argResults.wasParsed('concurrency')) {
-        globals.logger.printStatus(
+        globals.printStatus(
           '-j/--concurrency was parsed but will be ignored, this option is not '
           'supported when running Integration Tests.',
         );

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

@@ -190,7 +190,7 @@ class UpdatePackagesCommand extends FlutterCommand {
         if (pubspec.checksum.value == null) {
           // If the checksum is invalid or missing, we can just ask them run to run
           // upgrade again to compute it.
-          globals.printError(
+          globals.printWarning(
             'Warning: pubspec in ${directory.path} has out of date dependencies. '
             'Please run "flutter update-packages --force-upgrade" to update them correctly.'
           );
@@ -207,7 +207,7 @@ class UpdatePackagesCommand extends FlutterCommand {
         if (checksum != pubspec.checksum.value) {
           // If the checksum doesn't match, they may have added or removed some dependencies.
           // we need to run update-packages to recapture the transitive deps.
-          globals.printError(
+          globals.printWarning(
             'Warning: pubspec in ${directory.path} has updated or new dependencies. '
             'Please run "flutter update-packages --force-upgrade" to update them correctly '
             '(checksum ${pubspec.checksum.value} != $checksum).'
@@ -1501,7 +1501,7 @@ Directory createTemporaryFlutterSdk(
       ..createSync(recursive: true);
     final PubspecYaml pubspecYaml = pubspecsByName[flutterPackage];
     if (pubspecYaml == null) {
-      logger.printError(
+      logger.printWarning(
         "Unexpected package '$flutterPackage' found in packages directory",
       );
       continue;

packages/flutter_tools/lib/src/flutter_manifest.dart

@@ -339,11 +339,11 @@ class FlutterManifest {
       final YamlList? fontFiles = fontFamily['fonts'] as YamlList?;
       final String? familyName = fontFamily['family'] as String?;
       if (familyName == null) {
-        _logger.printError('Warning: Missing family name for font.', emphasis: true);
+        _logger.printWarning('Warning: Missing family name for font.', emphasis: true);
         continue;
       }
       if (fontFiles == null) {
-        _logger.printError('Warning: No fonts specified for font $familyName', emphasis: true);
+        _logger.printWarning('Warning: No fonts specified for font $familyName', emphasis: true);
         continue;
       }
 
@@ -351,7 +351,7 @@ class FlutterManifest {
       for (final Map<Object?, Object?> fontFile in fontFiles.cast<Map<Object?, Object?>>()) {
         final String? asset = fontFile['asset'] as String?;
         if (asset == null) {
-          _logger.printError('Warning: Missing asset in fonts for $familyName', emphasis: true);
+          _logger.printWarning('Warning: Missing asset in fonts for $familyName', emphasis: true);
           continue;
         }
 

packages/flutter_tools/lib/src/flutter_plugins.dart

@@ -393,7 +393,7 @@ Future<void> _writeAndroidPluginRegistrant(FlutterProject project, List<Plugin>
         }
       }
       if (pluginsUsingV1.length > 1) {
-        globals.printError(
+        globals.printWarning(
           'The plugins `${pluginsUsingV1.join(', ')}` use a deprecated version of the Android embedding.\n'
           'To avoid unexpected runtime failures, or future build failures, try to see if these plugins '
           'support the Android V2 embedding. Otherwise, consider removing them since a future release '
@@ -402,7 +402,7 @@ Future<void> _writeAndroidPluginRegistrant(FlutterProject project, List<Plugin>
           'https://flutter.dev/go/android-plugin-migration.'
         );
       } else if (pluginsUsingV1.isNotEmpty) {
-        globals.printError(
+        globals.printWarning(
           'The plugin `${pluginsUsingV1.first}` uses a deprecated version of the Android embedding.\n'
           'To avoid unexpected runtime failures, or future build failures, try to see if this plugin '
           'supports the Android V2 embedding. Otherwise, consider removing it since a future release '
@@ -414,7 +414,7 @@ Future<void> _writeAndroidPluginRegistrant(FlutterProject project, List<Plugin>
       templateContent = _androidPluginRegistryTemplateNewEmbedding;
       break;
     case AndroidEmbeddingVersion.v1:
-      globals.printError(
+      globals.printWarning(
         'This app is using a deprecated version of the Android embedding.\n'
         'To avoid unexpected runtime failures, or future build failures, try to migrate this '
         'app to the V2 embedding.\n'
@@ -1301,7 +1301,7 @@ Future<void> generateMainDartWithPluginRegistrant(
         newMainDart.deleteSync();
       }
     } on FileSystemException catch (error) {
-      globals.printError(
+      globals.printWarning(
         'Unable to remove ${newMainDart.path}, received error: $error.\n'
         'You might need to run flutter clean.'
       );

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

@@ -124,6 +124,10 @@ Future<void> _buildAssets(
     assetDirPath: assetDir,
   );
 
+  if (assets == null) {
+    throwToolExit('Unable to find assets.', exitCode: 1);
+  }
+
   final Map<String, DevFSContent> assetEntries =
       Map<String, DevFSContent>.of(assets.entries);
   await writeBundle(globals.fs.directory(assetDir), assetEntries);

packages/flutter_tools/lib/src/globals.dart

@@ -150,6 +150,30 @@ void printError(
   );
 }
 
+/// Display a warning level message to the user. Commands should use this if they
+/// have important warnings to convey that aren't fatal.
+///
+/// Set [emphasis] to true to make the output bold if it's supported.
+/// Set [color] to a [TerminalColor] to color the output, if the logger
+/// supports it. The [color] defaults to [TerminalColor.cyan].
+void printWarning(
+    String message, {
+      bool? emphasis,
+      TerminalColor? color,
+      int? indent,
+      int? hangingIndent,
+      bool? wrap,
+    }) {
+  logger.printWarning(
+    message,
+    emphasis: emphasis ?? false,
+    color: color,
+    indent: indent,
+    hangingIndent: hangingIndent,
+    wrap: wrap,
+  );
+}
+
 /// Display normal output of the command. This should be used for things like
 /// progress messages, success messages, or just normal command output.
 ///

packages/flutter_tools/lib/src/macos/cocoapods.dart

@@ -176,7 +176,7 @@ class CocoaPods {
     final CocoaPodsStatus installation = await evaluateCocoaPodsInstallation;
     switch (installation) {
       case CocoaPodsStatus.notInstalled:
-        _logger.printError(
+        _logger.printWarning(
           'Warning: CocoaPods not installed. Skipping pod install.\n'
           '$noCocoaPodsConsequence\n'
           'To install $cocoaPodsInstallInstructions\n',
@@ -184,7 +184,7 @@ class CocoaPods {
         );
         return false;
       case CocoaPodsStatus.brokenInstall:
-        _logger.printError(
+        _logger.printWarning(
           'Warning: CocoaPods is installed but broken. Skipping pod install.\n'
           '$brokenCocoaPodsConsequence\n'
           'To re-install $cocoaPodsInstallInstructions\n',
@@ -192,7 +192,7 @@ class CocoaPods {
         );
         return false;
       case CocoaPodsStatus.unknownVersion:
-        _logger.printError(
+        _logger.printWarning(
           'Warning: Unknown CocoaPods version installed.\n'
           '$unknownCocoaPodsConsequence\n'
           'To upgrade $cocoaPodsInstallInstructions\n',
@@ -200,7 +200,7 @@ class CocoaPods {
         );
         break;
       case CocoaPodsStatus.belowMinimumVersion:
-        _logger.printError(
+        _logger.printWarning(
           'Warning: CocoaPods minimum required version $cocoaPodsMinimumVersion or greater not installed. Skipping pod install.\n'
           '$noCocoaPodsConsequence\n'
           'To upgrade $cocoaPodsInstallInstructions\n',
@@ -208,7 +208,7 @@ class CocoaPods {
         );
         return false;
       case CocoaPodsStatus.belowRecommendedVersion:
-        _logger.printError(
+        _logger.printWarning(
           'Warning: CocoaPods recommended version $cocoaPodsRecommendedVersion or greater not installed.\n'
           'Pods handling may fail on some projects involving plugins.\n'
           'To upgrade $cocoaPodsInstallInstructions\n',
@@ -406,15 +406,15 @@ class CocoaPods {
     // plugin_pods = parse_KV_file('../.flutter-plugins')
     if (xcodeProject.podfile.existsSync() &&
       xcodeProject.podfile.readAsStringSync().contains(".flutter-plugins'")) {
-      const String error = 'Warning: Podfile is out of date\n'
+      const String warning = 'Warning: Podfile is out of date\n'
           '$outOfDatePluginsPodfileConsequence\n'
           'To regenerate the Podfile, run:\n';
       if (isIos) {
-        throwToolExit('$error\n$podfileIosMigrationInstructions\n');
+        throwToolExit('$warning\n$podfileIosMigrationInstructions\n');
       } else {
         // The old macOS Podfile will work until `.flutter-plugins` is removed.
         // Warn instead of exit.
-        _logger.printError('$error\n$podfileMacOSMigrationInstructions\n', emphasis: true);
+        _logger.printWarning('$warning\n$podfileMacOSMigrationInstructions\n', emphasis: true);
       }
     }
   }

packages/flutter_tools/lib/src/macos/xcdevice.dart

@@ -415,7 +415,7 @@ class XCDevice {
         } else {
           cpuArchitecture = DarwinArch.arm64;
         }
-        _logger.printError(
+        _logger.printWarning(
           'Unknown architecture $architecture, defaulting to '
           '${getNameForDarwinArch(cpuArchitecture)}',
         );

packages/flutter_tools/lib/src/mdns_discovery.dart

@@ -110,7 +110,7 @@ class MDnsObservatoryDiscovery {
         return null;
       }
       if (srv.length > 1) {
-        _logger.printError('Unexpectedly found more than one observatory report for $domainName '
+        _logger.printWarning('Unexpectedly found more than one observatory report for $domainName '
                    '- using first one (${srv.first.port}).');
       }
       _logger.printTrace('Checking for authentication code for $domainName');

packages/flutter_tools/lib/src/project.dart

@@ -479,23 +479,6 @@ class AndroidProject extends FlutterProjectPlatform {
   }
 
   Future<void> ensureReadyForPlatformSpecificTooling() async {
-    if (getEmbeddingVersion() == AndroidEmbeddingVersion.v1) {
-      globals.printStatus(
-"""
-━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
-Warning
-──────────────────────────────────────────────────────────────────────────────
-Your Flutter application is created using an older version of the Android
-embedding. It's being deprecated in favor of Android embedding v2. Follow the
-steps at
-
-https://flutter.dev/go/android-project-migration
-
-to migrate your project.
-━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
-"""
-      );
-    }
     if (isModule && _shouldRegenerateFromTemplate()) {
       await _regenerateLibrary();
       // Add ephemeral host app, if an editable host app does not already exist.

packages/flutter_tools/lib/src/resident_runner.dart

@@ -1178,7 +1178,7 @@ abstract class ResidentRunner extends ResidentHandlers {
     );
     if (!_lastBuild.success) {
       for (final ExceptionMeasurement exceptionMeasurement in _lastBuild.exceptions.values) {
-        globals.logger.printError(
+        globals.printError(
           exceptionMeasurement.exception.toString(),
           stackTrace: globals.logger.isVerbose
             ? exceptionMeasurement.stackTrace
@@ -1186,7 +1186,7 @@ abstract class ResidentRunner extends ResidentHandlers {
         );
       }
     }
-    globals.logger.printTrace('complete');
+    globals.printTrace('complete');
   }
 
   @protected
@@ -1241,7 +1241,7 @@ abstract class ResidentRunner extends ResidentHandlers {
     if (_dillOutputPath != null) {
       return;
     }
-    globals.logger.printTrace('Caching compiled dill');
+    globals.printTrace('Caching compiled dill');
     final File outputDill = globals.fs.file(dillOutputPath);
     if (outputDill.existsSync()) {
       final String copyPath = getDefaultCachedKernelPath(
@@ -1561,7 +1561,7 @@ class TerminalHandler {
         _logger.printTrace('Deleting pid file (${_actualPidFile.path}).');
         _actualPidFile.deleteSync();
       } on FileSystemException catch (error) {
-        _logger.printError('Failed to delete pid file (${_actualPidFile.path}): ${error.message}');
+        _logger.printWarning('Failed to delete pid file (${_actualPidFile.path}): ${error.message}');
       }
       _actualPidFile = null;
     }

packages/flutter_tools/lib/src/run_cold.dart

@@ -77,8 +77,8 @@ class ColdRunner extends ResidentRunner {
           return result;
         }
       }
-    } on Exception catch (err) {
+    } on Exception catch (err, stack) {
-      globals.printError(err.toString());
+      globals.printError('$err\n$stack');
       appFailedToStart();
       return 1;
     }

packages/flutter_tools/lib/src/runner/flutter_command.dart

@@ -115,6 +115,7 @@ class FlutterOptions {
   static const String kDeferredComponents = 'deferred-components';
   static const String kAndroidProjectArgs = 'android-project-arg';
   static const String kInitializeFromDill = 'initialize-from-dill';
+  static const String kFatalWarnings = 'fatal-warnings';
 }
 
 /// flutter command categories for usage.
@@ -178,6 +179,8 @@ abstract class FlutterCommand extends Command<void> {
 
   bool _usesIpv6Flag = false;
 
+  bool _usesFatalWarnings = false;
+
   bool get shouldRunPub => _usesPubOption && boolArg('pub');
 
   bool get shouldUpdateCache => true;
@@ -271,6 +274,15 @@ abstract class FlutterCommand extends Command<void> {
     _usesTargetOption = true;
   }
 
+  void usesFatalWarningsOption({ required bool verboseHelp }) {
+    argParser.addFlag(FlutterOptions.kFatalWarnings,
+        hide: !verboseHelp,
+        help: 'Causes the command to fail if warnings are sent to the console '
+              'during its execution.'
+    );
+    _usesFatalWarnings = true;
+  }
+
   String get targetFile {
     if (argResults?.wasParsed('target') == true) {
       return stringArg('target')!;
@@ -413,10 +425,10 @@ abstract class FlutterCommand extends Command<void> {
       // TODO(ianh): enable the following code once google3 is migrated away from --disable-dds (and add test to flutter_command_test.dart)
       if (false) { // ignore: dead_code
         if (ddsEnabled) {
-          globals.printError('${globals.logger.terminal
+          globals.printWarning('${globals.logger.terminal
               .warningMark} The "--no-disable-dds" argument is deprecated and redundant, and should be omitted.');
         } else {
-          globals.printError('${globals.logger.terminal
+          globals.printWarning('${globals.logger.terminal
               .warningMark} The "--disable-dds" argument is deprecated. Use "--no-dds" instead.');
         }
       }
@@ -1123,6 +1135,9 @@ abstract class FlutterCommand extends Command<void> {
       name: 'command',
       overrides: <Type, Generator>{FlutterCommand: () => this},
       body: () async {
+        if (_usesFatalWarnings) {
+          globals.logger.fatalWarnings = boolArg(FlutterOptions.kFatalWarnings);
+        }
         // Prints the welcome message if needed.
         globals.flutterUsage.printWelcome();
         _printDeprecationWarning();
@@ -1139,6 +1154,9 @@ abstract class FlutterCommand extends Command<void> {
           if (commandPath != null) {
             _sendPostUsage(commandPath, commandResult, startTime, endTime);
           }
+          if (_usesFatalWarnings) {
+            globals.logger.checkForFatalLogs();
+          }
         }
       },
     );
@@ -1146,13 +1164,12 @@ abstract class FlutterCommand extends Command<void> {
 
   void _printDeprecationWarning() {
     if (deprecated) {
-      globals.printError(
+      globals.printWarning(
         '${globals.logger.terminal.warningMark} The "$name" command is deprecated and '
         'will be removed in a future version of Flutter. '
         'See https://flutter.dev/docs/development/tools/sdk/releases '
-        'for previous releases of Flutter.',
+        'for previous releases of Flutter.\n',
       );
-      globals.printError('');
     }
   }
 

packages/flutter_tools/lib/src/version.dart

@@ -277,10 +277,10 @@ class FlutterVersion {
       );
     } on VersionCheckError catch (error) {
       if (globals.platform.environment.containsKey('FLUTTER_GIT_URL')) {
-        globals.logger.printError('Warning: the Flutter git upstream was overridden '
+        globals.printWarning('Warning: the Flutter git upstream was overridden '
         'by the environment variable FLUTTER_GIT_URL = ${globals.flutterGit}');
       }
-      globals.logger.printError(error.toString());
+      globals.printError(error.toString());
       rethrow;
     } finally {
       await _removeVersionCheckRemoteIfExists();

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

@@ -568,6 +568,20 @@ class StreamLogger extends Logger {
     int hangingIndent,
     bool wrap,
   }) {
+    hadErrorOutput = true;
+    _log('[stderr] $message');
+  }
+
+  @override
+  void printWarning(
+    String message, {
+    bool emphasis,
+    TerminalColor color,
+    int indent,
+    int hangingIndent,
+    bool wrap,
+  }) {
+    hadWarningOutput = true;
     _log('[stderr] $message');
   }
 

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

@@ -227,6 +227,8 @@ void main() {
       const <String>['build', 'linux', '--debug', '--no-pub']
     );
     expect(testLogger.statusText, isNot(contains('STDOUT STUFF')));
+    expect(testLogger.warningText, isNot(contains('STDOUT STUFF')));
+    expect(testLogger.errorText, isNot(contains('STDOUT STUFF')));
     expect(testLogger.traceText, contains('STDOUT STUFF'));
   }, overrides: <Type, Generator>{
     FileSystem: () => fileSystem,
@@ -308,6 +310,8 @@ ERROR: No file or variants found for asset: images/a_dot_burr.jpeg
     );
     expect(testLogger.statusText, contains('STDOUT STUFF'));
     expect(testLogger.traceText, isNot(contains('STDOUT STUFF')));
+    expect(testLogger.warningText, isNot(contains('STDOUT STUFF')));
+    expect(testLogger.errorText, isNot(contains('STDOUT STUFF')));
   }, overrides: <Type, Generator>{
     FileSystem: () => fileSystem,
     ProcessManager: () => processManager,

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

@@ -3,9 +3,13 @@
 // found in the LICENSE file.
 
 // @dart = 2.8
-
 import 'package:args/command_runner.dart';
+import 'package:file/memory.dart';
+import 'package:flutter_tools/src/base/file_system.dart';
+import 'package:flutter_tools/src/cache.dart';
+import 'package:flutter_tools/src/commands/build.dart';
 import 'package:flutter_tools/src/runner/flutter_command.dart';
+import 'package:meta/meta.dart';
 
 import '../../src/common.dart';
 import '../../src/context.dart';
@@ -13,27 +17,97 @@ import '../../src/test_flutter_command_runner.dart';
 
 void main() {
   testUsingContext('obfuscate requires split-debug-info', () {
-    final FakeBuildCommand command = FakeBuildCommand();
+    final FakeBuildInfoCommand command = FakeBuildInfoCommand();
     final CommandRunner<void> commandRunner = createTestCommandRunner(command);
 
     expect(() => commandRunner.run(<String>[
-      'build',
+      'fake',
       '--obfuscate',
-    ]), throwsToolExit());
+    ]), throwsToolExit(message: '"--${FlutterOptions.kDartObfuscationOption}" can only be used in '
+        'combination with "--${FlutterOptions.kSplitDebugInfoOption}"'));
+  });
+  group('Fatal Logs', () {
+    FakeBuildCommand command;
+    MemoryFileSystem fs;
+
+    setUp(() {
+      fs = MemoryFileSystem.test();
+      fs.file('/package/pubspec.yaml').createSync(recursive: true);
+      fs.currentDirectory = '/package';
+      Cache.disableLocking();
+    });
+
+    testUsingContext("doesn't fail if --fatal-warnings specified and no warnings occur", () async {
+      command = FakeBuildCommand();
+      try {
+        await createTestCommandRunner(command).run(<String>[
+          'build',
+          'test',
+          '--${FlutterOptions.kFatalWarnings}',
+        ]);
+      } on Exception {
+        fail('Unexpected exception thrown');
+      }
+    }, overrides: <Type, Generator>{
+      FileSystem: () => fs,
+      ProcessManager: () => FakeProcessManager.any(),
+    });
+
+    testUsingContext("doesn't fail if --fatal-warnings not specified", () async {
+      command = FakeBuildCommand();
+      testLogger.printWarning('Warning: Mild annoyance Will Robinson!');
+      try {
+        await createTestCommandRunner(command).run(<String>[
+          'build',
+          'test',
+        ]);
+      } on Exception {
+        fail('Unexpected exception thrown');
+      }
+    }, overrides: <Type, Generator>{
+      FileSystem: () => fs,
+      ProcessManager: () => FakeProcessManager.any(),
+    });
+
+    testUsingContext('fails if --fatal-warnings specified and warnings emitted', () async {
+      command = FakeBuildCommand();
+      testLogger.printWarning('Warning: Mild annoyance Will Robinson!');
+      await expectLater(createTestCommandRunner(command).run(<String>[
+        'build',
+        'test',
+        '--${FlutterOptions.kFatalWarnings}',
+      ]), throwsToolExit(message: 'Logger received warning output during the run, and "--${FlutterOptions.kFatalWarnings}" is enabled.'));
+    }, overrides: <Type, Generator>{
+      FileSystem: () => fs,
+      ProcessManager: () => FakeProcessManager.any(),
+    });
+
+    testUsingContext('fails if --fatal-warnings specified and errors emitted', () async {
+      command = FakeBuildCommand();
+      testLogger.printError('Error: Danger Will Robinson!');
+      await expectLater(createTestCommandRunner(command).run(<String>[
+        'build',
+        'test',
+        '--${FlutterOptions.kFatalWarnings}',
+      ]), throwsToolExit(message: 'Logger received error output during the run, and "--${FlutterOptions.kFatalWarnings}" is enabled.'));
+    }, overrides: <Type, Generator>{
+      FileSystem: () => fs,
+      ProcessManager: () => FakeProcessManager.any(),
+    });
   });
 }
 
-class FakeBuildCommand extends FlutterCommand {
+class FakeBuildInfoCommand extends FlutterCommand {
-  FakeBuildCommand() {
+  FakeBuildInfoCommand() : super() {
     addSplitDebugInfoOption();
     addDartObfuscationOption();
   }
 
   @override
-  String get description => throw UnimplementedError();
+  String get description => '';
 
   @override
-  String get name => 'build';
+  String get name => 'fake';
 
   @override
   Future<FlutterCommandResult> runCommand() async {
@@ -41,3 +115,35 @@ class FakeBuildCommand extends FlutterCommand {
     return FlutterCommandResult.success();
   }
 }
+
+class FakeBuildCommand extends BuildCommand {
+  FakeBuildCommand({bool verboseHelp = false}) : super(verboseHelp: verboseHelp) {
+    addSubcommand(FakeBuildSubcommand(verboseHelp: verboseHelp));
+  }
+
+  @override
+  String get description => '';
+
+  @override
+  String get name => 'build';
+
+  @override
+  Future<FlutterCommandResult> runCommand() async {
+    return FlutterCommandResult.success();
+  }
+}
+
+class FakeBuildSubcommand extends BuildSubCommand {
+  FakeBuildSubcommand({@required bool verboseHelp}) : super(verboseHelp: verboseHelp);
+
+  @override
+  String get description => '';
+
+  @override
+  String get name => 'test';
+
+  @override
+  Future<FlutterCommandResult> runCommand() async {
+    return FlutterCommandResult.success();
+  }
+}

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

@@ -130,6 +130,29 @@ void main() {
       Logger: () => notifyingLogger,
     });
 
+    testUsingContext('printWarning should send daemon.logMessage event', () async {
+      final StreamController<Map<String, dynamic>> commands = StreamController<Map<String, dynamic>>();
+      final StreamController<Map<String, dynamic>> responses = StreamController<Map<String, dynamic>>();
+      daemon = Daemon(
+        commands.stream,
+        responses.add,
+        notifyingLogger: notifyingLogger,
+      );
+      globals.printWarning('daemon.logMessage test');
+      final Map<String, dynamic> response = await responses.stream.firstWhere((Map<String, dynamic> map) {
+        return map['event'] == 'daemon.logMessage' && (map['params'] as Map<String, dynamic>)['level'] == 'warning';
+      });
+      expect(response['id'], isNull);
+      expect(response['event'], 'daemon.logMessage');
+      final Map<String, String> logMessage = castStringKeyedMap(response['params']).cast<String, String>();
+      expect(logMessage['level'], 'warning');
+      expect(logMessage['message'], 'daemon.logMessage test');
+      await responses.close();
+      await commands.close();
+    }, overrides: <Type, Generator>{
+      Logger: () => notifyingLogger,
+    });
+
     testUsingContext('printStatus should log to stdout when logToStdout is enabled', () async {
       final StringBuffer buffer = await capturedConsolePrint(() {
         final StreamController<Map<String, dynamic>> commands = StreamController<Map<String, dynamic>>();

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

@@ -294,6 +294,75 @@ void main() {
       });
     });
 
+    group('Fatal Logs', () {
+      TestRunCommandWithFakeResidentRunner command;
+      MemoryFileSystem fs;
+
+      setUp(() {
+        command = TestRunCommandWithFakeResidentRunner()
+          ..fakeResidentRunner = FakeResidentRunner();
+        fs = MemoryFileSystem.test();
+      });
+
+      testUsingContext("doesn't fail if --fatal-warnings specified and no warnings occur", () async {
+        try {
+          await createTestCommandRunner(command).run(<String>[
+            'run',
+            '--no-pub',
+            '--no-hot',
+            '--${FlutterOptions.kFatalWarnings}',
+          ]);
+        } on Exception {
+          fail('Unexpected exception thrown');
+        }
+      }, overrides: <Type, Generator>{
+        FileSystem: () => fs,
+        ProcessManager: () => FakeProcessManager.any(),
+      });
+
+      testUsingContext("doesn't fail if --fatal-warnings not specified", () async {
+        testLogger.printWarning('Warning: Mild annoyance Will Robinson!');
+        try {
+          await createTestCommandRunner(command).run(<String>[
+            'run',
+            '--no-pub',
+            '--no-hot',
+          ]);
+        } on Exception {
+          fail('Unexpected exception thrown');
+        }
+      }, overrides: <Type, Generator>{
+        FileSystem: () => fs,
+        ProcessManager: () => FakeProcessManager.any(),
+      });
+
+      testUsingContext('fails if --fatal-warnings specified and warnings emitted', () async {
+        testLogger.printWarning('Warning: Mild annoyance Will Robinson!');
+        await expectLater(createTestCommandRunner(command).run(<String>[
+          'run',
+          '--no-pub',
+          '--no-hot',
+          '--${FlutterOptions.kFatalWarnings}',
+        ]), throwsToolExit(message: 'Logger received warning output during the run, and "--${FlutterOptions.kFatalWarnings}" is enabled.'));
+      }, overrides: <Type, Generator>{
+        FileSystem: () => fs,
+        ProcessManager: () => FakeProcessManager.any(),
+      });
+
+      testUsingContext('fails if --fatal-warnings specified and errors emitted', () async {
+        testLogger.printError('Error: Danger Will Robinson!');
+        await expectLater(createTestCommandRunner(command).run(<String>[
+          'run',
+          '--no-pub',
+          '--no-hot',
+          '--${FlutterOptions.kFatalWarnings}',
+        ]), throwsToolExit(message: 'Logger received error output during the run, and "--${FlutterOptions.kFatalWarnings}" is enabled.'));
+      }, overrides: <Type, Generator>{
+        FileSystem: () => fs,
+        ProcessManager: () => FakeProcessManager.any(),
+      });
+    });
+
     testUsingContext('should only request artifacts corresponding to connected devices', () async {
       mockDeviceManager.devices = <Device>[FakeDevice(targetPlatform: TargetPlatform.android_arm)];
 
@@ -496,7 +565,7 @@ class FakeDevice extends Fake implements Device {
   @override
   String get id => 'fake_device';
 
-  void _throwToolExit(int code) => throwToolExit(null, exitCode: code);
+  void _throwToolExit(int code) => throwToolExit('FakeDevice tool exit', exitCode: code);
 
   @override
   Future<bool> get isLocalEmulator => Future<bool>.value(_isLocalEmulator);
@@ -504,6 +573,9 @@ class FakeDevice extends Fake implements Device {
   @override
   bool supportsRuntimeMode(BuildMode mode) => true;
 
+  @override
+  Future<bool> get supportsHardwareRendering async => true;
+
   @override
   bool supportsHotReload = false;
 
@@ -542,7 +614,7 @@ class FakeDevice extends Fake implements Device {
   @override
   final PlatformType platformType = PlatformType.ios;
 
-  bool startAppSuccess = true;
+  bool startAppSuccess;
 
   @override
   DevFSWriter createDevFSWriter(
@@ -564,9 +636,12 @@ class FakeDevice extends Fake implements Device {
     bool ipv6 = false,
     String userIdentifier,
   }) async {
-    if (!startAppSuccess) {
+    if (startAppSuccess == false) {
       return LaunchResult.failed();
     }
+    if (startAppSuccess == true) {
+      return LaunchResult.succeeded();
+    }
     final String dartFlags = debuggingOptions.dartFlags;
     // In release mode, --dart-flags should be set to the empty string and
     // provided flags should be dropped. In debug and profile modes,
@@ -587,18 +662,20 @@ class FakeDevice extends Fake implements Device {
 }
 
 class FakeApplicationPackageFactory extends Fake implements ApplicationPackageFactory {
-  ApplicationPackage package;
+  FakeApplicationPackageFactory(this.applicationPackage);
+
+  ApplicationPackage applicationPackage;
 
   @override
   Future<ApplicationPackage> getPackageForPlatform(
-    TargetPlatform platform, {
+      TargetPlatform platform, {
-    BuildInfo buildInfo,
+        BuildInfo buildInfo,
-    File applicationBinary,
+        File applicationBinary,
-  }) async {
+      }) async => applicationPackage;
-    return package;
-  }
 }
 
+class FakeApplicationPackage extends Fake implements ApplicationPackage { }
+
 class TestRunCommandWithFakeResidentRunner extends RunCommand {
   FakeResidentRunner fakeResidentRunner;
 

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

@@ -16,6 +16,7 @@ import 'package:flutter_tools/src/cache.dart';
 import 'package:flutter_tools/src/commands/test.dart';
 import 'package:flutter_tools/src/device.dart';
 import 'package:flutter_tools/src/project.dart';
+import 'package:flutter_tools/src/runner/flutter_command.dart';
 import 'package:flutter_tools/src/test/runner.dart';
 import 'package:flutter_tools/src/test/test_wrapper.dart';
 import 'package:flutter_tools/src/test/watcher.dart';
@@ -644,6 +645,60 @@ dev_dependencies:
     ProcessManager: () => FakeProcessManager.any(),
     DeviceManager: () => _FakeDeviceManager(<Device>[]),
   });
+
+  group('Fatal Logs', () {
+    testUsingContext("doesn't fail when --fatal-warnings is set and no warning output", () async {
+      final FakeFlutterTestRunner testRunner = FakeFlutterTestRunner(0);
+
+      final TestCommand testCommand = TestCommand(testRunner: testRunner);
+      final CommandRunner<void> commandRunner = createTestCommandRunner(testCommand);
+
+      try {
+        await commandRunner.run(const <String>[
+          'test',
+          '--no-pub',
+          '--${FlutterOptions.kFatalWarnings}',
+        ]);
+      } on Exception {
+        fail('Unexpected exception thrown');
+      }
+    }, overrides: <Type, Generator>{
+      FileSystem: () => fs,
+      ProcessManager: () => FakeProcessManager.any(),
+    });
+    testUsingContext('fails if --fatal-warnings specified and warnings emitted', () async {
+      final FakeFlutterTestRunner testRunner = FakeFlutterTestRunner(0);
+
+      final TestCommand testCommand = TestCommand(testRunner: testRunner);
+      final CommandRunner<void> commandRunner = createTestCommandRunner(testCommand);
+
+      testLogger.printWarning('Warning: Mild annoyance, Will Robinson!');
+      expect(commandRunner.run(const <String>[
+        'test',
+        '--no-pub',
+        '--${FlutterOptions.kFatalWarnings}',
+      ]), throwsToolExit(message: 'Logger received warning output during the run, and "--${FlutterOptions.kFatalWarnings}" is enabled.'));
+    }, overrides: <Type, Generator>{
+      FileSystem: () => fs,
+      ProcessManager: () => FakeProcessManager.any(),
+    });
+    testUsingContext('fails when --fatal-warnings is set and only errors emitted', () async {
+      final FakeFlutterTestRunner testRunner = FakeFlutterTestRunner(0);
+
+      final TestCommand testCommand = TestCommand(testRunner: testRunner);
+      final CommandRunner<void> commandRunner = createTestCommandRunner(testCommand);
+
+      testLogger.printError('Error: Danger Will Robinson!');
+      expect(commandRunner.run(const <String>[
+        'test',
+        '--no-pub',
+        '--${FlutterOptions.kFatalWarnings}',
+      ]), throwsToolExit(message: 'Logger received error output during the run, and "--${FlutterOptions.kFatalWarnings}" is enabled.'));
+    }, overrides: <Type, Generator>{
+      FileSystem: () => fs,
+      ProcessManager: () => FakeProcessManager.any(),
+    });
+  });
 }
 
 class FakeFlutterTestRunner implements FlutterTestRunner {

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

@@ -311,7 +311,7 @@ flutter:
 
     await writeBundle(directory, <String, DevFSContent>{}, loggerOverride: testLogger);
 
-    expect(testLogger.errorText, contains('Expected Error Text'));
+    expect(testLogger.warningText, contains('Expected Error Text'));
   });
 
   testUsingContext('does not unnecessarily recreate asset manifest, font manifest, license', () async {

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

@@ -137,7 +137,7 @@ void main() {
       final FakeSimpleArtifact artifact = FakeSimpleArtifact(cache);
       await artifact.update(FakeArtifactUpdater(), logger, fileSystem, FakeOperatingSystemUtils());
 
-      expect(logger.errorText, contains('stamp write failed'));
+      expect(logger.warningText, contains('stamp write failed'));
     });
 
     testWithoutContext('Continues on missing version file', () async {
@@ -153,7 +153,7 @@ void main() {
       final FakeSimpleArtifact artifact = FakeSimpleArtifact(cache);
       await artifact.update(FakeArtifactUpdater(), logger, fileSystem, FakeOperatingSystemUtils());
 
-      expect(logger.errorText, contains('No known version for the artifact name "fake"'));
+      expect(logger.warningText, contains('No known version for the artifact name "fake"'));
     });
 
     testWithoutContext('Gradle wrapper should not be up to date, if some cached artifact is not available', () {
@@ -725,7 +725,7 @@ void main() {
 
     cache.clearStampFiles();
 
-    expect(logger.errorText, contains('Failed to delete some stamp files'));
+    expect(logger.warningText, contains('Failed to delete some stamp files'));
   });
 
   testWithoutContext('FlutterWebSdk fetches web artifacts and deletes previous directory contents', () async {

packages/flutter_tools/test/general.shard/commands/build_test.dart

@@ -83,6 +83,8 @@ void main() {
 }
 
 class FakeBuildSubCommand extends BuildSubCommand {
+  FakeBuildSubCommand() : super(verboseHelp: false);
+
   @override
   String get description => throw UnimplementedError();
 

packages/flutter_tools/test/general.shard/macos/cocoapods_test.dart

@@ -432,8 +432,8 @@ void main() {
         buildMode: BuildMode.debug,
       );
 
-      expect(logger.errorText, contains('Warning: Podfile is out of date'));
+      expect(logger.warningText, contains('Warning: Podfile is out of date'));
-      expect(logger.errorText, contains('rm macos/Podfile'));
+      expect(logger.warningText, contains('rm macos/Podfile'));
       expect(fakeProcessManager, hasNoRemainingExpectations);
     });
 

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

@@ -747,7 +747,7 @@ dependencies:
           .childFile('GeneratedPluginRegistrant.java');
         expect(registrant.readAsStringSync(),
           contains('plugin3.UseOldEmbedding.registerWith(shimPluginRegistry.registrarFor("plugin3.UseOldEmbedding"));'));
-        expect(testLogger.errorText, equals(
+        expect(testLogger.warningText, equals(
           'The plugin `plugin3` uses a deprecated version of the Android embedding.\n'
           'To avoid unexpected runtime failures, or future build failures, try to see if this plugin supports the Android V2 embedding. '
           'Otherwise, consider removing it since a future release of Flutter will remove these deprecated APIs.\n'
@@ -827,7 +827,7 @@ dependencies:
 
         await injectPlugins(flutterProject, androidPlatform: true);
 
-        expect(testLogger.errorText, equals(
+        expect(testLogger.warningText, equals(
           'This app is using a deprecated version of the Android embedding.\n'
           'To avoid unexpected runtime failures, or future build failures, try to migrate this app to the V2 embedding.\n'
           'Take a look at the docs for migrating an app: https://github.com/flutter/flutter/wiki/Upgrading-pre-1.12-Android-projects\n'
@@ -854,7 +854,7 @@ dependencies:
           contains('plugin3.UseOldEmbedding.registerWith(shimPluginRegistry.registrarFor("plugin3.UseOldEmbedding"));'));
         expect(registrant.readAsStringSync(),
           contains('plugin4.UseOldEmbedding.registerWith(shimPluginRegistry.registrarFor("plugin4.UseOldEmbedding"));'));
-        expect(testLogger.errorText, equals(
+        expect(testLogger.warningText, equals(
           'The plugins `plugin3, plugin4` use a deprecated version of the Android embedding.\n'
           'To avoid unexpected runtime failures, or future build failures, try to see if these plugins support the Android V2 embedding. '
           'Otherwise, consider removing them since a future release of Flutter will remove these deprecated APIs.\n'
@@ -882,7 +882,7 @@ dependencies:
           contains('plugin3.UseOldEmbedding.registerWith(shimPluginRegistry.registrarFor("plugin3.UseOldEmbedding"));'));
         expect(registrant.readAsStringSync(),
           contains('plugin4.UseOldEmbedding.registerWith(shimPluginRegistry.registrarFor("plugin4.UseOldEmbedding"));'));
-        expect(testLogger.errorText, equals(
+        expect(testLogger.warningText, equals(
           'The plugins `plugin3, plugin4` use a deprecated version of the Android embedding.\n'
           'To avoid unexpected runtime failures, or future build failures, try to see if these plugins support the Android V2 embedding. '
           'Otherwise, consider removing them since a future release of Flutter will remove these deprecated APIs.\n'

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

@@ -183,7 +183,7 @@ void main() {
         // android:name="flutterEmbedding" android:value="2" />.
 
         await project.regeneratePlatformSpecificTooling();
-        expect(testLogger.statusText, contains('https://flutter.dev/go/android-project-migration'));
+        expect(testLogger.warningText, contains('https://github.com/flutter/flutter/wiki/Upgrading-pre-1.12-Android-projects'));
       });
       _testInMemory('Android plugin without example app does not show a warning', () async {
         final FlutterProject project = await aPluginProject();

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

@@ -87,7 +87,7 @@ void main() {
       final CommandRunner<void> runner = createTestCommandRunner(flutterCommand);
       await runner.run(<String>['deprecated']);
 
-      expect(testLogger.errorText,
+      expect(testLogger.warningText,
         contains('The "deprecated" command is deprecated and will be removed in '
             'a future version of Flutter.'));
       expect(flutterCommand.usage,

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

@@ -129,7 +129,7 @@ void main() {
 
     // We get a warning about the unexpected package.
     expect(
-      bufferLogger.errorText,
+      bufferLogger.warningText,
       contains("Unexpected package 'extra' found in packages directory"),
     );
 

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

@@ -10,12 +10,15 @@ import 'package:file/file.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/io.dart';
 import 'package:flutter_tools/src/base/logger.dart';
+import 'package:flutter_tools/src/base/os.dart';
 import 'package:flutter_tools/src/base/terminal.dart';
 import 'package:flutter_tools/src/cache.dart';
 import 'package:process/process.dart';
+import 'package:test/fake.dart';
 
 import '../src/common.dart';
 import '../src/context.dart';
+import '../src/fakes.dart';
 import 'test_utils.dart';
 
 final String dart = fileSystem.path
@@ -24,53 +27,122 @@ final String dart = fileSystem.path
 void main() {
   group('Cache.lock', () {
     // Windows locking is too flaky for this to work reliably.
-    if (!platform.isWindows) {
+    if (platform.isWindows) {
-      testWithoutContext(
+      return;
-          'should log a message to stderr when lock is not acquired', () async {
+    }
-        final String oldRoot = Cache.flutterRoot;
+    testWithoutContext(
-        final Directory tempDir = fileSystem.systemTempDirectory.createTempSync('cache_test.');
+        'should log a message to stderr when lock is not acquired', () async {
-        final BufferLogger logger = BufferLogger(
+      final String oldRoot = Cache.flutterRoot;
-          terminal: Terminal.test(supportsColor: false, supportsEmoji: false),
+      final Directory tempDir = fileSystem.systemTempDirectory.createTempSync('cache_test.');
-          outputPreferences: OutputPreferences(),
+      final BufferLogger logger = BufferLogger(
+        terminal: Terminal.test(supportsColor: false, supportsEmoji: false),
+        outputPreferences: OutputPreferences(),
+      );
+      logger.fatalWarnings = true;
+      try {
+        Cache.flutterRoot = tempDir.absolute.path;
+        final Cache cache = Cache.test(
+          fileSystem: fileSystem,
+          processManager: FakeProcessManager.any(),
+          logger: logger,
         );
-        try {
+        final File cacheFile = fileSystem.file(fileSystem.path
-          Cache.flutterRoot = tempDir.absolute.path;
+            .join(Cache.flutterRoot, 'bin', 'cache', 'lockfile'))
-          final Cache cache = Cache.test(
+          ..createSync(recursive: true);
-            fileSystem: fileSystem,
+        final File script = fileSystem.file(fileSystem.path
-            processManager: FakeProcessManager.any(),
+            .join(Cache.flutterRoot, 'bin', 'cache', 'test_lock.dart'));
-            logger: logger,
+        script.writeAsStringSync(r'''
-          );
-          final File cacheFile = fileSystem.file(fileSystem.path
-              .join(Cache.flutterRoot, 'bin', 'cache', 'lockfile'))
-            ..createSync(recursive: true);
-          final File script = fileSystem.file(fileSystem.path
-              .join(Cache.flutterRoot, 'bin', 'cache', 'test_lock.dart'));
-          script.writeAsStringSync(r'''
 import 'dart:async';
 import 'dart:io';
 
 Future<void> main(List<String> args) async {
-  File file = File(args[0]);
+File file = File(args[0]);
-  RandomAccessFile lock = file.openSync(mode: FileMode.write);
+RandomAccessFile lock = file.openSync(mode: FileMode.write);
-  lock.lockSync();
+lock.lockSync();
-  await Future<void>.delayed(const Duration(milliseconds: 1000));
+await Future<void>.delayed(const Duration(milliseconds: 1000));
-  exit(0);
+exit(0);
 }
 ''');
-          final Process process = await const LocalProcessManager().start(
+        final Process process = await const LocalProcessManager().start(
-            <String>[dart, script.absolute.path, cacheFile.absolute.path],
+          <String>[dart, script.absolute.path, cacheFile.absolute.path],
-          );
+        );
-          await Future<void>.delayed(const Duration(milliseconds: 500));
+        await Future<void>.delayed(const Duration(milliseconds: 500));
-          await cache.lock();
+        await cache.lock();
-          process.kill(io.ProcessSignal.sigkill);
+        process.kill(io.ProcessSignal.sigkill);
-        } finally {
+      } finally {
-          tryToDelete(tempDir);
+        tryToDelete(tempDir);
-          Cache.flutterRoot = oldRoot;
+        Cache.flutterRoot = oldRoot;
-        }
+      }
-        expect(logger.statusText, isEmpty);
+      expect(logger.statusText, isEmpty);
-        expect(logger.errorText,
+      expect(logger.errorText, isEmpty);
-            equals('Waiting for another flutter command to release the startup lock...\n'));
+      expect(logger.warningText,
-      });
+          equals('Waiting for another flutter command to release the startup lock...\n'));
-    }
+      expect(logger.hadErrorOutput, isFalse);
+      // Should still be false, since the particular "Waiting..." message above aims to
+      // avoid triggering failure as a fatal warning.
+      expect(logger.hadWarningOutput, isFalse);
+    });
+    testWithoutContext(
+        'should log a warning message for unknown version ', () async {
+      final String oldRoot = Cache.flutterRoot;
+      final Directory tempDir = fileSystem.systemTempDirectory.createTempSync('cache_test.');
+      final BufferLogger logger = BufferLogger(
+        terminal: Terminal.test(supportsColor: false, supportsEmoji: false),
+        outputPreferences: OutputPreferences(),
+      );
+      logger.fatalWarnings = true;
+      try {
+        Cache.flutterRoot = tempDir.absolute.path;
+        final Cache cache = Cache.test(
+          fileSystem: fileSystem,
+          processManager: FakeProcessManager.any(),
+          logger: logger,
+        );
+        final FakeVersionlessArtifact artifact = FakeVersionlessArtifact(cache);
+        cache.registerArtifact(artifact);
+        await artifact.update(FakeArtifactUpdater(), logger, fileSystem, FakeOperatingSystemUtils());
+      } finally {
+        tryToDelete(tempDir);
+        Cache.flutterRoot = oldRoot;
+      }
+      expect(logger.statusText, isEmpty);
+      expect(logger.warningText, equals('No known version for the artifact name "fake". '
+        'Flutter can continue, but the artifact may be re-downloaded on '
+        'subsequent invocations until the problem is resolved.\n'));
+      expect(logger.hadErrorOutput, isFalse);
+      expect(logger.hadWarningOutput, isTrue);
+    });
   });
 }
+
+class FakeArtifactUpdater extends Fake implements ArtifactUpdater {
+  void Function(String, Uri, Directory) onDownloadZipArchive;
+  void Function(String, Uri, Directory) onDownloadZipTarball;
+
+  @override
+  Future<void> downloadZippedTarball(String message, Uri url, Directory location) async {
+    onDownloadZipTarball?.call(message, url, location);
+  }
+
+  @override
+  Future<void> downloadZipArchive(String message, Uri url, Directory location) async {
+    onDownloadZipArchive?.call(message, url, location);
+  }
+
+  @override
+  void removeDownloadedFiles() { }
+}
+
+class FakeVersionlessArtifact extends CachedArtifact {
+  FakeVersionlessArtifact(Cache cache) : super(
+    'fake',
+    cache,
+    DevelopmentArtifact.universal,
+  );
+
+  @override
+  String get version => null;
+
+  @override
+  Future<void> updateInner(ArtifactUpdater artifactUpdater, FileSystem fileSystem, OperatingSystemUtils operatingSystemUtils) async { }
+}

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

@@ -115,84 +115,66 @@ void main() {
   testWithoutContext('flutter test should run a test when its name matches a regexp', () async {
     final ProcessResult result = await _runFlutterTest('filtering', automatedTestsDirectory, flutterTestDirectory,
       extraArguments: const <String>['--name', 'inc.*de']);
-    if (!(result.stdout as String).contains('+1: All tests passed')) {
+    expect(result.stdout, contains(RegExp(r'\+\d+: All tests passed!')));
-      fail('unexpected output from test:\n\n${result.stdout}\n-- end stdout --\n\n');
-    }
     expect(result.exitCode, 0);
   });
 
   testWithoutContext('flutter test should run a test when its name contains a string', () async {
     final ProcessResult result = await _runFlutterTest('filtering', automatedTestsDirectory, flutterTestDirectory,
       extraArguments: const <String>['--plain-name', 'include']);
-    if (!(result.stdout as String).contains('+1: All tests passed')) {
+    expect(result.stdout, contains(RegExp(r'\+\d+: All tests passed!')));
-      fail('unexpected output from test:\n\n${result.stdout}\n-- end stdout --\n\n');
-    }
     expect(result.exitCode, 0);
   });
 
   testWithoutContext('flutter test should run a test with a given tag', () async {
     final ProcessResult result = await _runFlutterTest('filtering_tag', automatedTestsDirectory, flutterTestDirectory,
         extraArguments: const <String>['--tags', 'include-tag']);
-    if (!(result.stdout as String).contains('+1: All tests passed')) {
+    expect(result.stdout, contains(RegExp(r'\+\d+: All tests passed!')));
-      fail('unexpected output from test:\n\n${result.stdout}\n-- end stdout --\n\n');
-    }
     expect(result.exitCode, 0);
   });
 
   testWithoutContext('flutter test should not run a test with excluded tag', () async {
     final ProcessResult result = await _runFlutterTest('filtering_tag', automatedTestsDirectory, flutterTestDirectory,
         extraArguments: const <String>['--exclude-tags', 'exclude-tag']);
-    if (!(result.stdout as String).contains('+1: All tests passed')) {
+    expect(result.stdout, contains(RegExp(r'\+\d+: All tests passed!')));
-      fail('unexpected output from test:\n\n${result.stdout}\n-- end stdout --\n\n');
-    }
     expect(result.exitCode, 0);
   });
 
   testWithoutContext('flutter test should run all tests when tags are unspecified', () async {
     final ProcessResult result = await _runFlutterTest('filtering_tag', automatedTestsDirectory, flutterTestDirectory);
-    if (!(result.stdout as String).contains('+1 -1: Some tests failed')) {
+    expect(result.stdout, contains(RegExp(r'\+\d+ -1: Some tests failed\.')));
-      fail('unexpected output from test:\n\n${result.stdout}\n-- end stdout --\n\n');
-    }
     expect(result.exitCode, 1);
   });
 
   testWithoutContext('flutter test should run a widgetTest with a given tag', () async {
     final ProcessResult result = await _runFlutterTest('filtering_tag_widget', automatedTestsDirectory, flutterTestDirectory,
         extraArguments: const <String>['--tags', 'include-tag']);
-    if (!(result.stdout as String).contains('+1: All tests passed')) {
+    expect(result.stdout, contains(RegExp(r'\+\d+: All tests passed!')));
-      fail('unexpected output from test:\n\n${result.stdout}\n-- end stdout --\n\n');
-    }
     expect(result.exitCode, 0);
   });
 
   testWithoutContext('flutter test should not run a widgetTest with excluded tag', () async {
     final ProcessResult result = await _runFlutterTest('filtering_tag_widget', automatedTestsDirectory, flutterTestDirectory,
         extraArguments: const <String>['--exclude-tags', 'exclude-tag']);
-    if (!(result.stdout as String).contains('+1: All tests passed')) {
+    expect(result.stdout, contains(RegExp(r'\+\d+: All tests passed!')));
-      fail('unexpected output from test:\n\n${result.stdout}\n-- end stdout --\n\n');
-    }
     expect(result.exitCode, 0);
   });
 
   testWithoutContext('flutter test should run all widgetTest when tags are unspecified', () async {
     final ProcessResult result = await _runFlutterTest('filtering_tag_widget', automatedTestsDirectory, flutterTestDirectory);
-    if (!(result.stdout as String).contains('+1 -1: Some tests failed')) {
+    expect(result.stdout, contains(RegExp(r'\+\d+ -1: Some tests failed\.')));
-      fail('unexpected output from test:\n\n${result.stdout}\n-- end stdout --\n\n');
-    }
     expect(result.exitCode, 1);
   });
 
   testWithoutContext('flutter test should test runs to completion', () async {
     final ProcessResult result = await _runFlutterTest('trivial', automatedTestsDirectory, flutterTestDirectory,
       extraArguments: const <String>['--verbose']);
-    final String stdout = result.stdout as String;
+    final String stdout = (result.stdout as String).replaceAll('\r', '\n');
-    if ((!stdout.contains('+1: All tests passed')) ||
+    expect(stdout, contains(RegExp(r'\+\d+: All tests passed\!')));
-        (!stdout.contains('test 0: Starting flutter_tester process with command')) ||
+    expect(stdout, contains('test 0: Starting flutter_tester process with command'));
-        (!stdout.contains('test 0: deleting temporary directory')) ||
+    expect(stdout, contains('test 0: deleting temporary directory'));
-        (!stdout.contains('test 0: finished')) ||
+    expect(stdout, contains('test 0: finished'));
-        (!stdout.contains('test package returned with exit code 0'))) {
+    expect(stdout, contains('test package returned with exit code 0'));
-      fail('unexpected output from test:\n\n${result.stdout}\n-- end stdout --\n\n');
-    }
     if ((result.stderr as String).isNotEmpty) {
       fail('unexpected error output from test:\n\n${result.stderr}\n-- end stderr --\n\n');
     }
@@ -202,14 +184,12 @@ void main() {
   testWithoutContext('flutter test should run all tests inside of a directory with no trailing slash', () async {
     final ProcessResult result = await _runFlutterTest(null, automatedTestsDirectory, '$flutterTestDirectory/child_directory',
       extraArguments: const <String>['--verbose']);
-    final String stdout = result.stdout as String;
+    final String stdout = (result.stdout as String).replaceAll('\r', '\n');
-    if ((!stdout.contains('+2: All tests passed')) ||
+    expect(result.stdout, contains(RegExp(r'\+\d+: All tests passed\!')));
-        (!stdout.contains('test 0: Starting flutter_tester process with command')) ||
+    expect(stdout, contains('test 0: Starting flutter_tester process with command'));
-        (!stdout.contains('test 0: deleting temporary directory')) ||
+    expect(stdout, contains('test 0: deleting temporary directory'));
-        (!stdout.contains('test 0: finished')) ||
+    expect(stdout, contains('test 0: finished'));
-        (!stdout.contains('test package returned with exit code 0'))) {
+    expect(stdout, contains('test package returned with exit code 0'));
-      fail('unexpected output from test:\n\n${result.stdout}\n-- end stdout --\n\n');
-    }
     if ((result.stderr as String).isNotEmpty) {
       fail('unexpected error output from test:\n\n${result.stderr}\n-- end stderr --\n\n');
     }