[flutter_tools] migrate io, process, logger, terminal (#78816)

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

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 /// This file serves as the single point of entry into the `dart:io` APIs
 /// within Flutter tools.
 ///
@@ -140,7 +138,7 @@ bool _inUnitTest() {
 /// Sets the [exit] function to a function that throws an exception rather
 /// than exiting the process; this is intended for testing purposes.
 @visibleForTesting
-void setExitFunctionForTests([ ExitFunction exitFunction ]) {
+void setExitFunctionForTests([ ExitFunction? exitFunction ]) {
   _exitFunction = exitFunction ?? (int exitCode) {
     throw ProcessExit(exitCode, immediate: true);
   };
@@ -235,12 +233,12 @@ class Stdio {
   /// dart:io.
   @visibleForTesting
   Stdio.test({
-    @required io.Stdout stdout,
-    @required io.IOSink stderr,
+    required io.Stdout stdout,
+    required io.IOSink stderr,
   }) : _stdoutOverride = stdout, _stderrOverride = stderr;
 
-  io.Stdout _stdoutOverride;
-  io.IOSink _stderrOverride;
+  io.Stdout? _stdoutOverride;
+  io.IOSink? _stderrOverride;
 
   // These flags exist to remember when the done Futures on stdout and stderr
   // complete to avoid trying to write to a closed stream sink, which would
@@ -253,34 +251,34 @@ class Stdio {
   @visibleForTesting
   io.Stdout get stdout {
     if (_stdout != null) {
-      return _stdout;
+      return _stdout!;
     }
     _stdout = _stdoutOverride ?? io.stdout;
-    _stdout.done.then(
+    _stdout!.done.then(
       (void _) { _stdoutDone = true; },
       onError: (Object err, StackTrace st) { _stdoutDone = true; },
     );
-    return _stdout;
+    return _stdout!;
   }
-  io.Stdout _stdout;
+  io.Stdout? _stdout;
 
   @visibleForTesting
   io.IOSink get stderr {
     if (_stderr != null) {
-      return _stderr;
+      return _stderr!;
     }
     _stderr = _stderrOverride ?? io.stderr;
-    _stderr.done.then(
+    _stderr!.done.then(
       (void _) { _stderrDone = true; },
       onError: (Object err, StackTrace st) { _stderrDone = true; },
     );
-    return _stderr;
+    return _stderr!;
   }
-  io.IOSink _stderr;
+  io.IOSink? _stderr;
 
   bool get hasTerminal => io.stdout.hasTerminal;
 
-  static bool _stdinHasTerminal;
+  static bool? _stdinHasTerminal;
 
   /// Determines whether there is a terminal attached.
   ///
@@ -290,7 +288,7 @@ class Stdio {
   /// runtime errors such as "inappropriate ioctl for device" if not handled.
   bool get stdinHasTerminal {
     if (_stdinHasTerminal != null) {
-      return _stdinHasTerminal;
+      return _stdinHasTerminal!;
     }
     if (stdin is! io.Stdin) {
       return _stdinHasTerminal = false;
@@ -309,15 +307,15 @@ class Stdio {
     return _stdinHasTerminal = true;
   }
 
-  int get terminalColumns => hasTerminal ? stdout.terminalColumns : null;
-  int get terminalLines => hasTerminal ? stdout.terminalLines : null;
+  int? get terminalColumns => hasTerminal ? stdout.terminalColumns : null;
+  int? get terminalLines => hasTerminal ? stdout.terminalLines : null;
   bool get supportsAnsiEscapes => hasTerminal && stdout.supportsAnsiEscapes;
 
   /// Writes [message] to [stderr], falling back on [fallback] if the write
   /// throws any exception. The default fallback calls [print] on [message].
   void stderrWrite(
     String message, {
-    void Function(String, dynamic, StackTrace) fallback,
+    void Function(String, dynamic, StackTrace)? fallback,
   }) {
     if (!_stderrDone) {
       _stdioWrite(stderr, message, fallback: fallback);
@@ -334,7 +332,7 @@ class Stdio {
   /// throws any exception. The default fallback calls [print] on [message].
   void stdoutWrite(
     String message, {
-    void Function(String, dynamic, StackTrace) fallback,
+    void Function(String, dynamic, StackTrace)? fallback,
   }) {
     if (!_stdoutDone) {
       _stdioWrite(stdout, message, fallback: fallback);
@@ -349,7 +347,7 @@ class Stdio {
 
   // Helper for [stderrWrite] and [stdoutWrite].
   void _stdioWrite(io.IOSink sink, String message, {
-    void Function(String, dynamic, StackTrace) fallback,
+    void Function(String, dynamic, StackTrace)? fallback,
   }) {
     asyncGuard<void>(() async {
       sink.write(message);
@@ -447,7 +445,7 @@ typedef NetworkInterfaceLister = Future<List<NetworkInterface>> Function({
   io.InternetAddressType type,
 });
 
-NetworkInterfaceLister _networkInterfaceListerOverride;
+NetworkInterfaceLister? _networkInterfaceListerOverride;
 
 // Tests can set up a non-default network interface lister.
 @visibleForTesting
@@ -469,7 +467,7 @@ Future<List<NetworkInterface>> listNetworkInterfaces({
   io.InternetAddressType type = io.InternetAddressType.any,
 }) async {
   if (_networkInterfaceListerOverride != null) {
-    return _networkInterfaceListerOverride(
+    return _networkInterfaceListerOverride!.call(
       includeLoopback: includeLoopback,
       includeLinkLocal: includeLinkLocal,
       type: type,

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

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 
 import 'package:meta/meta.dart';
@@ -65,12 +63,12 @@ abstract class Logger {
   /// `outputPreferences.wrapText` setting.
   void printError(
     String message, {
-    StackTrace stackTrace,
-    bool emphasis,
-    TerminalColor color,
-    int indent,
-    int hangingIndent,
-    bool wrap,
+    StackTrace? stackTrace,
+    bool? emphasis,
+    TerminalColor? color,
+    int? indent,
+    int? hangingIndent,
+    bool? wrap,
   });
 
   /// Display normal output of the command. This should be used for things like
@@ -103,12 +101,12 @@ abstract class Logger {
   /// `outputPreferences.wrapText` setting.
   void printStatus(
     String message, {
-    bool emphasis,
-    TerminalColor color,
-    bool newline,
-    int indent,
-    int hangingIndent,
-    bool wrap,
+    bool? emphasis,
+    TerminalColor? color,
+    bool? newline,
+    int? indent,
+    int? hangingIndent,
+    bool? wrap,
   });
 
   /// Use this for verbose tracing output. Users can turn this output on in order
@@ -126,20 +124,20 @@ abstract class Logger {
   /// between the `message` and the progress indicator, if any.
   Status startProgress(
     String message, {
-    String progressId,
+    String? progressId,
     bool multilineOutput = false,
     int progressIndicatorPadding = kDefaultStatusPadding,
   });
 
   /// A [SilentStatus] or an [AnsiSpinner] (depending on whether the
   /// terminal is fancy enough), already started.
-  Status startSpinner({ VoidCallback onFinish });
+  Status startSpinner({ VoidCallback? onFinish });
 
   /// Send an event to be emitted.
   ///
   /// Only surfaces a value in machine modes, Loggers may ignore this message in
   /// non-machine modes.
-  void sendEvent(String name, [Map<String, dynamic> args]) { }
+  void sendEvent(String name, [Map<String, dynamic>? args]) { }
 
   /// Clears all output.
   void clear();
@@ -174,7 +172,14 @@ class DelegatingLogger implements Logger {
   bool get isVerbose => _delegate.isVerbose;
 
   @override
-  void printError(String message, {StackTrace stackTrace, bool emphasis, TerminalColor color, int indent, int hangingIndent, bool wrap}) {
+  void printError(String message, {
+    StackTrace? stackTrace,
+    bool? emphasis,
+    TerminalColor? color,
+    int? indent,
+    int? hangingIndent,
+    bool? wrap,
+  }) {
     _delegate.printError(
       message,
       stackTrace: stackTrace,
@@ -187,7 +192,14 @@ class DelegatingLogger implements Logger {
   }
 
   @override
-  void printStatus(String message, {bool emphasis, TerminalColor color, bool newline, int indent, int hangingIndent, bool wrap}) {
+  void printStatus(String message, {
+    bool? emphasis,
+    TerminalColor? color,
+    bool? newline,
+    int? indent,
+    int? hangingIndent,
+    bool? wrap,
+  }) {
     _delegate.printStatus(message,
       emphasis: emphasis,
       color: color,
@@ -204,12 +216,16 @@ class DelegatingLogger implements Logger {
   }
 
   @override
-  void sendEvent(String name, [Map<String, dynamic> args]) {
+  void sendEvent(String name, [Map<String, dynamic>? args]) {
     _delegate.sendEvent(name, args);
   }
 
   @override
-  Status startProgress(String message, {String progressId, bool multilineOutput = false, int progressIndicatorPadding = kDefaultStatusPadding}) {
+  Status startProgress(String message, {
+    String? progressId,
+    bool multilineOutput = false,
+    int progressIndicatorPadding = kDefaultStatusPadding,
+  }) {
     return _delegate.startProgress(message,
       progressId: progressId,
       multilineOutput: multilineOutput,
@@ -218,7 +234,7 @@ class DelegatingLogger implements Logger {
   }
 
   @override
-  Status startSpinner({VoidCallback onFinish}) {
+  Status startSpinner({VoidCallback? onFinish}) {
     return _delegate.startSpinner(onFinish: onFinish);
   }
 
@@ -240,7 +256,7 @@ T asLogger<T extends Logger>(Logger logger) {
     if (logger is T) {
       return logger;
     } else if (logger is DelegatingLogger) {
-      logger = (logger as DelegatingLogger)._delegate;
+      logger = logger._delegate;
     } else {
       throw StateError('$original has no ancestor delegate of type $T');
     }
@@ -249,9 +265,9 @@ T asLogger<T extends Logger>(Logger logger) {
 
 class StdoutLogger extends Logger {
   StdoutLogger({
-    @required this.terminal,
-    @required Stdio stdio,
-    @required OutputPreferences outputPreferences,
+    required this.terminal,
+    required Stdio stdio,
+    required OutputPreferences outputPreferences,
     StopwatchFactory stopwatchFactory = const StopwatchFactory(),
   })
     : _stdio = stdio,
@@ -265,7 +281,7 @@ class StdoutLogger extends Logger {
   final Stdio _stdio;
   final StopwatchFactory _stopwatchFactory;
 
-  Status _status;
+  Status? _status;
 
   @override
   bool get isVerbose => false;
@@ -279,15 +295,14 @@ class StdoutLogger extends Logger {
   @override
   void printError(
     String message, {
-    StackTrace stackTrace,
-    bool emphasis,
-    TerminalColor color,
-    int indent,
-    int hangingIndent,
-    bool wrap,
+    StackTrace? stackTrace,
+    bool? emphasis,
+    TerminalColor? color,
+    int? indent,
+    int? hangingIndent,
+    bool? wrap,
   }) {
     _status?.pause();
-    message ??= '';
     message = wrapText(message,
       indent: indent,
       hangingIndent: hangingIndent,
@@ -308,15 +323,14 @@ class StdoutLogger extends Logger {
   @override
   void printStatus(
     String message, {
-    bool emphasis,
-    TerminalColor color,
-    bool newline,
-    int indent,
-    int hangingIndent,
-    bool wrap,
+    bool? emphasis,
+    TerminalColor? color,
+    bool? newline,
+    int? indent,
+    int? hangingIndent,
+    bool? wrap,
   }) {
     _status?.pause();
-    message ??= '';
     message = wrapText(message,
       indent: indent,
       hangingIndent: hangingIndent,
@@ -348,11 +362,10 @@ class StdoutLogger extends Logger {
   @override
   Status startProgress(
     String message, {
-    String progressId,
+    String? progressId,
     bool multilineOutput = false,
     int progressIndicatorPadding = kDefaultStatusPadding,
   }) {
-    assert(progressIndicatorPadding != null);
     if (_status != null) {
       // Ignore nested progresses; return a no-op status object.
       return SilentStatus(
@@ -379,11 +392,11 @@ class StdoutLogger extends Logger {
         stopwatch: _stopwatchFactory.createStopwatch(),
       )..start();
     }
-    return _status;
+    return _status!;
   }
 
   @override
-  Status startSpinner({ VoidCallback onFinish }) {
+  Status startSpinner({ VoidCallback? onFinish }) {
     if (terminal.supportsColor) {
       return AnsiSpinner(
         onFinish: onFinish,
@@ -403,7 +416,7 @@ class StdoutLogger extends Logger {
   }
 
   @override
-  void sendEvent(String name, [Map<String, dynamic> args]) { }
+  void sendEvent(String name, [Map<String, dynamic>? args]) { }
 
   @override
   void clear() {
@@ -423,9 +436,9 @@ class StdoutLogger extends Logger {
 /// they will show up as the unrepresentable character symbol '�'.
 class WindowsStdoutLogger extends StdoutLogger {
   WindowsStdoutLogger({
-    @required Terminal terminal,
-    @required Stdio stdio,
-    @required OutputPreferences outputPreferences,
+    required Terminal terminal,
+    required Stdio stdio,
+    required OutputPreferences outputPreferences,
     StopwatchFactory stopwatchFactory = const StopwatchFactory(),
   }) : super(
       terminal: terminal,
@@ -451,16 +464,16 @@ class WindowsStdoutLogger extends StdoutLogger {
 
 class BufferLogger extends Logger {
   BufferLogger({
-    @required this.terminal,
-    @required OutputPreferences outputPreferences,
+    required this.terminal,
+    required OutputPreferences outputPreferences,
     StopwatchFactory stopwatchFactory = const StopwatchFactory(),
   }) : _outputPreferences = outputPreferences,
        _stopwatchFactory = stopwatchFactory;
 
   /// Create a [BufferLogger] with test preferences.
   BufferLogger.test({
-    Terminal terminal,
-    OutputPreferences outputPreferences,
+    Terminal? terminal,
+    OutputPreferences? outputPreferences,
   }) : terminal = terminal ?? Terminal.test(),
        _outputPreferences = outputPreferences ?? OutputPreferences.test(),
        _stopwatchFactory = const StopwatchFactory();
@@ -496,12 +509,12 @@ class BufferLogger extends Logger {
   @override
   void printError(
     String message, {
-    StackTrace stackTrace,
-    bool emphasis,
-    TerminalColor color,
-    int indent,
-    int hangingIndent,
-    bool wrap,
+    StackTrace? stackTrace,
+    bool? emphasis,
+    TerminalColor? color,
+    int? indent,
+    int? hangingIndent,
+    bool? wrap,
   }) {
     _error.writeln(terminal.color(
       wrapText(message,
@@ -517,12 +530,12 @@ class BufferLogger extends Logger {
   @override
   void printStatus(
     String message, {
-    bool emphasis,
-    TerminalColor color,
-    bool newline,
-    int indent,
-    int hangingIndent,
-    bool wrap,
+    bool? emphasis,
+    TerminalColor? color,
+    bool? newline,
+    int? indent,
+    int? hangingIndent,
+    bool? wrap,
   }) {
     if (newline != false) {
       _status.writeln(wrapText(message,
@@ -547,7 +560,7 @@ class BufferLogger extends Logger {
   @override
   Status startProgress(
     String message, {
-    String progressId,
+    String? progressId,
     bool multilineOutput = false,
     int progressIndicatorPadding = kDefaultStatusPadding,
   }) {
@@ -559,7 +572,7 @@ class BufferLogger extends Logger {
   }
 
   @override
-  Status startSpinner({VoidCallback onFinish}) {
+  Status startSpinner({VoidCallback? onFinish}) {
     return SilentStatus(
       stopwatch: _stopwatchFactory.createStopwatch(),
       onFinish: onFinish,
@@ -575,8 +588,8 @@ class BufferLogger extends Logger {
   }
 
   @override
-  void sendEvent(String name, [Map<String, dynamic> args]) {
-    _events.write(json.encode(<String, Object>{
+  void sendEvent(String name, [Map<String, dynamic>? args]) {
+    _events.write(json.encode(<String, Object?>{
       'name': name,
       'args': args
     }));
@@ -602,12 +615,12 @@ class VerboseLogger extends DelegatingLogger {
   @override
   void printError(
     String message, {
-    StackTrace stackTrace,
-    bool emphasis,
-    TerminalColor color,
-    int indent,
-    int hangingIndent,
-    bool wrap,
+    StackTrace? stackTrace,
+    bool? emphasis,
+    TerminalColor? color,
+    int? indent,
+    int? hangingIndent,
+    bool? wrap,
   }) {
     _emit(
       _LogType.error,
@@ -624,12 +637,12 @@ class VerboseLogger extends DelegatingLogger {
   @override
   void printStatus(
     String message, {
-    bool emphasis,
-    TerminalColor color,
-    bool newline,
-    int indent,
-    int hangingIndent,
-    bool wrap,
+    bool? emphasis,
+    TerminalColor? color,
+    bool? newline,
+    int? indent,
+    int? hangingIndent,
+    bool? wrap,
   }) {
     _emit(_LogType.status, wrapText(message,
       indent: indent,
@@ -647,7 +660,7 @@ class VerboseLogger extends DelegatingLogger {
   @override
   Status startProgress(
     String message, {
-    String progressId,
+    String? progressId,
     bool multilineOutput = false,
     int progressIndicatorPadding = kDefaultStatusPadding,
   }) {
@@ -669,7 +682,7 @@ class VerboseLogger extends DelegatingLogger {
     )..start();
   }
 
-  void _emit(_LogType type, String message, [ StackTrace stackTrace ]) {
+  void _emit(_LogType type, String message, [ StackTrace? stackTrace ]) {
     if (message.trim().isEmpty) {
       return;
     }
@@ -705,7 +718,7 @@ class VerboseLogger extends DelegatingLogger {
   }
 
   @override
-  void sendEvent(String name, [Map<String, dynamic> args]) { }
+  void sendEvent(String name, [Map<String, dynamic>? args]) { }
 }
 
 class PrefixedErrorLogger extends DelegatingLogger {
@@ -714,14 +727,14 @@ class PrefixedErrorLogger extends DelegatingLogger {
   @override
   void printError(
     String message, {
-    StackTrace stackTrace,
-    bool emphasis,
-    TerminalColor color,
-    int indent,
-    int hangingIndent,
-    bool wrap,
+    StackTrace? stackTrace,
+    bool? emphasis,
+    TerminalColor? color,
+    int? indent,
+    int? hangingIndent,
+    bool? wrap,
   }) {
-    if (message?.trim()?.isNotEmpty == true) {
+    if (message.trim().isNotEmpty == true) {
       message = 'ERROR: $message';
     }
     super.printError(
@@ -760,10 +773,10 @@ typedef SlowWarningCallback = String Function();
 abstract class Status {
   Status({
     this.onFinish,
-    @required Stopwatch stopwatch,
+    required Stopwatch stopwatch,
   }) : _stopwatch = stopwatch;
 
-  final VoidCallback onFinish;
+  final VoidCallback? onFinish;
 
   @protected
   final Stopwatch _stopwatch;
@@ -802,17 +815,15 @@ abstract class Status {
   void finish() {
     assert(_stopwatch.isRunning);
     _stopwatch.stop();
-    if (onFinish != null) {
-      onFinish();
-    }
+    onFinish?.call();
   }
 }
 
 /// A [SilentStatus] shows nothing.
 class SilentStatus extends Status {
   SilentStatus({
-    @required Stopwatch stopwatch,
-    VoidCallback onFinish,
+    required Stopwatch stopwatch,
+    VoidCallback? onFinish,
   }) : super(
     onFinish: onFinish,
     stopwatch: stopwatch,
@@ -820,9 +831,7 @@ class SilentStatus extends Status {
 
   @override
   void finish() {
-    if (onFinish != null) {
-      onFinish();
-    }
+    onFinish?.call();
   }
 }
 
@@ -831,13 +840,11 @@ class SilentStatus extends Status {
 class SummaryStatus extends Status {
   SummaryStatus({
     this.message = '',
-    @required Stopwatch stopwatch,
+    required Stopwatch stopwatch,
     this.padding = kDefaultStatusPadding,
-    VoidCallback onFinish,
-    @required Stdio stdio,
-  }) : assert(message != null),
-       assert(padding != null),
-       _stdio = stdio,
+    VoidCallback? onFinish,
+    required Stdio stdio,
+  }) : _stdio = stdio,
        super(
          onFinish: onFinish,
          stopwatch: stopwatch,
@@ -899,10 +906,10 @@ class SummaryStatus extends Status {
 /// terminal spinner. When stopped or canceled, the animation erases itself.
 class AnsiSpinner extends Status {
   AnsiSpinner({
-    @required Stopwatch stopwatch,
-    @required Terminal terminal,
-    VoidCallback onFinish,
-    @required Stdio stdio,
+    required Stopwatch stopwatch,
+    required Terminal terminal,
+    VoidCallback? onFinish,
+    required Stdio stdio,
   }) : _stdio = stdio,
        _terminal = terminal,
        super(
@@ -918,7 +925,7 @@ class AnsiSpinner extends Status {
   bool timedOut = false;
 
   int ticks = 0;
-  Timer timer;
+  Timer? timer;
 
   // Windows console font has a limited set of Unicode characters.
   List<String> get _animation => !_terminal.supportsEmoji
@@ -945,7 +952,7 @@ class AnsiSpinner extends Status {
   void _startSpinner() {
     _writeToStdOut(_clear); // for _callback to backspace over
     timer = Timer.periodic(const Duration(milliseconds: 100), _callback);
-    _callback(timer);
+    _callback(timer!);
   }
 
   void _callback(Timer timer) {
@@ -960,8 +967,8 @@ class AnsiSpinner extends Status {
   @override
   void finish() {
     assert(timer != null);
-    assert(timer.isActive);
-    timer.cancel();
+    assert(timer!.isActive);
+    timer?.cancel();
     timer = null;
     _clearSpinner();
     super.finish();
@@ -974,15 +981,15 @@ class AnsiSpinner extends Status {
   @override
   void pause() {
     assert(timer != null);
-    assert(timer.isActive);
+    assert(timer!.isActive);
     _clearSpinner();
-    timer.cancel();
+    timer?.cancel();
   }
 
   @override
   void resume() {
     assert(timer != null);
-    assert(!timer.isActive);
+    assert(!timer!.isActive);
     _startSpinner();
   }
 }
@@ -1000,10 +1007,10 @@ class AnsiStatus extends AnsiSpinner {
     this.message = '',
     this.multilineOutput = false,
     this.padding = kDefaultStatusPadding,
-    @required Stopwatch stopwatch,
-    @required Terminal terminal,
-    VoidCallback onFinish,
-    Stdio stdio,
+    required Stopwatch stopwatch,
+    required Terminal terminal,
+    VoidCallback? onFinish,
+    required Stdio stdio,
   }) : assert(message != null),
        assert(multilineOutput != null),
        assert(padding != null),
@@ -1023,7 +1030,7 @@ class AnsiStatus extends AnsiSpinner {
   @override
   int get spinnerIndent => _kTimePadding - 1;
 
-  int _totalMessageLength;
+  int _totalMessageLength = 0;
 
   @override
   void start() {

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

@@ -2,11 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 
-import 'package:meta/meta.dart';
 import 'package:process/process.dart';
 
 import '../convert.dart';
@@ -27,7 +24,7 @@ typedef ShutdownHook = FutureOr<dynamic> Function();
 
 abstract class ShutdownHooks {
   factory ShutdownHooks({
-    @required Logger logger,
+    required Logger logger,
   }) => _DefaultShutdownHooks(
     logger: logger,
   );
@@ -49,7 +46,7 @@ abstract class ShutdownHooks {
 
 class _DefaultShutdownHooks implements ShutdownHooks {
   _DefaultShutdownHooks({
-    @required Logger logger,
+    required Logger logger,
   }) : _logger = logger;
 
   final Logger _logger;
@@ -137,8 +134,8 @@ typedef RunResultChecker = bool Function(int);
 
 abstract class ProcessUtils {
   factory ProcessUtils({
-    @required ProcessManager processManager,
-    @required Logger logger,
+    required ProcessManager processManager,
+    required Logger logger,
   }) => _DefaultProcessUtils(
     processManager: processManager,
     logger: logger,
@@ -236,8 +233,8 @@ abstract class ProcessUtils {
 
 class _DefaultProcessUtils implements ProcessUtils {
   _DefaultProcessUtils({
-    @required ProcessManager processManager,
-    @required Logger logger,
+    required ProcessManager processManager,
+    required Logger logger,
   }) : _processManager = processManager,
       _logger = logger;
 
@@ -249,11 +246,11 @@ class _DefaultProcessUtils implements ProcessUtils {
   Future<RunResult> run(
     List<String> cmd, {
     bool throwOnError = false,
-    RunResultChecker allowedFailures,
-    String workingDirectory,
+    RunResultChecker? allowedFailures,
+    String? workingDirectory,
     bool allowReentrantFlutter = false,
-    Map<String, String> environment,
-    Duration timeout,
+    Map<String, String>? environment,
+    Duration? timeout,
     int timeoutRetries = 0,
   }) async {
     if (cmd == null || cmd.isEmpty) {
@@ -305,8 +302,8 @@ class _DefaultProcessUtils implements ProcessUtils {
           .listen(stderrBuffer.write)
           .asFuture<void>(null);
 
-      int exitCode;
-      exitCode = await process.exitCode.timeout(timeout, onTimeout: () {
+      int? exitCode;
+      exitCode = await process.exitCode.then<int?>((int x) => x).timeout(timeout, onTimeout: () {
         // The process timed out. Kill it.
         _processManager.killPid(process.pid);
         return null;
@@ -324,7 +321,7 @@ class _DefaultProcessUtils implements ProcessUtils {
           stdioFuture = stdioFuture.timeout(const Duration(seconds: 1));
         }
         await stdioFuture;
-      } on Exception catch (_) {
+      } on Exception {
         // Ignore errors on the process' stdout and stderr streams. Just capture
         // whatever we got, and use the exit code
       }
@@ -365,10 +362,10 @@ class _DefaultProcessUtils implements ProcessUtils {
     List<String> cmd, {
     bool throwOnError = false,
     bool verboseExceptions = false,
-    RunResultChecker allowedFailures,
+    RunResultChecker? allowedFailures,
     bool hideStdout = false,
-    String workingDirectory,
-    Map<String, String> environment,
+    String? workingDirectory,
+    Map<String, String>? environment,
     bool allowReentrantFlutter = false,
     Encoding encoding = systemEncoding,
   }) {
@@ -420,9 +417,9 @@ class _DefaultProcessUtils implements ProcessUtils {
   @override
   Future<Process> start(
     List<String> cmd, {
-    String workingDirectory,
+    String? workingDirectory,
     bool allowReentrantFlutter = false,
-    Map<String, String> environment,
+    Map<String, String>? environment,
   }) {
     _traceCommand(cmd, workingDirectory: workingDirectory);
     return _processManager.start(
@@ -435,14 +432,14 @@ class _DefaultProcessUtils implements ProcessUtils {
   @override
   Future<int> stream(
     List<String> cmd, {
-    String workingDirectory,
+    String? workingDirectory,
     bool allowReentrantFlutter = false,
     String prefix = '',
     bool trace = false,
-    RegExp filter,
-    RegExp stdoutErrorMatcher,
-    StringConverter mapFunction,
-    Map<String, String> environment,
+    RegExp? filter,
+    RegExp? stdoutErrorMatcher,
+    StringConverter? mapFunction,
+    Map<String, String>? environment,
   }) async {
     final Process process = await start(
       cmd,
@@ -503,7 +500,7 @@ class _DefaultProcessUtils implements ProcessUtils {
   @override
   bool exitsHappySync(
     List<String> cli, {
-    Map<String, String> environment,
+    Map<String, String>? environment,
   }) {
     _traceCommand(cli);
     if (!_processManager.canRun(cli.first)) {
@@ -522,7 +519,7 @@ class _DefaultProcessUtils implements ProcessUtils {
   @override
   Future<bool> exitsHappy(
     List<String> cli, {
-    Map<String, String> environment,
+    Map<String, String>? environment,
   }) async {
     _traceCommand(cli);
     if (!_processManager.canRun(cli.first)) {
@@ -538,8 +535,8 @@ class _DefaultProcessUtils implements ProcessUtils {
     }
   }
 
-  Map<String, String> _environment(bool allowReentrantFlutter, [
-    Map<String, String> environment,
+  Map<String, String>? _environment(bool allowReentrantFlutter, [
+    Map<String, String>? environment,
   ]) {
     if (allowReentrantFlutter) {
       if (environment == null) {
@@ -552,7 +549,7 @@ class _DefaultProcessUtils implements ProcessUtils {
     return environment;
   }
 
-  void _traceCommand(List<String> args, { String workingDirectory }) {
+  void _traceCommand(List<String> args, { String? workingDirectory }) {
     final String argsText = args.join(' ');
     if (workingDirectory == null) {
       _logger.printTrace('executing: $argsText');

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

@@ -2,10 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
-import 'package:meta/meta.dart';
-
 import '../convert.dart';
 import 'io.dart' as io;
 import 'logger.dart';
@@ -25,12 +21,12 @@ enum TerminalColor {
 /// console.
 class OutputPreferences {
   OutputPreferences({
-    bool wrapText,
-    int wrapColumn,
-    bool showColor,
-    io.Stdio stdio,
+    bool? wrapText,
+    int? wrapColumn,
+    bool? showColor,
+    io.Stdio? stdio,
   }) : _stdio = stdio,
-       wrapText = wrapText ?? stdio.hasTerminal,
+       wrapText = wrapText ?? stdio?.hasTerminal ?? false,
        _overrideWrapColumn = wrapColumn,
        showColor = showColor ?? false;
 
@@ -38,7 +34,7 @@ class OutputPreferences {
   OutputPreferences.test({this.wrapText = false, int wrapColumn = kDefaultTerminalColumns, this.showColor = false})
     : _overrideWrapColumn = wrapColumn, _stdio = null;
 
-  final io.Stdio _stdio;
+  final io.Stdio? _stdio;
 
   /// If [wrapText] is true, then any text sent to the context's [Logger]
   /// instance (e.g. from the [printError] or [printStatus] functions) will be
@@ -56,7 +52,7 @@ class OutputPreferences {
   /// (e.g. from the [printError] or [printStatus] functions) will be wrapped.
   /// Ignored if [wrapText] is false. Defaults to the width of the output
   /// terminal, or to [kDefaultTerminalColumns] if not writing to a terminal.
-  final int _overrideWrapColumn;
+  final int? _overrideWrapColumn;
   int get wrapColumn {
     return _overrideWrapColumn ?? _stdio?.terminalColumns ?? kDefaultTerminalColumns;
   }
@@ -136,17 +132,17 @@ abstract class Terminal {
   /// If [usesTerminalUi] is false, throws a [StateError].
   Future<String> promptForCharInput(
     List<String> acceptedCharacters, {
-    @required Logger logger,
-    String prompt,
-    int defaultChoiceIndex,
+    required Logger logger,
+    String? prompt,
+    int? defaultChoiceIndex,
     bool displayAcceptedCharacters = true,
   });
 }
 
 class AnsiTerminal implements Terminal {
   AnsiTerminal({
-    @required io.Stdio stdio,
-    @required Platform platform,
+    required io.Stdio stdio,
+    required Platform platform,
   })
     : _stdio = stdio,
       _platform = platform;
@@ -178,10 +174,10 @@ class AnsiTerminal implements Terminal {
     TerminalColor.grey: grey,
   };
 
-  static String colorCode(TerminalColor color) => _colorMap[color];
+  static String colorCode(TerminalColor color) => _colorMap[color]!;
 
   @override
-  bool get supportsColor => _platform?.stdoutSupportsAnsi ?? false;
+  bool get supportsColor => _platform.stdoutSupportsAnsi;
 
   // Assume unicode emojis are supported when not on Windows.
   // If we are on Windows, unicode emojis are supported in Windows Terminal,
@@ -236,7 +232,7 @@ class AnsiTerminal implements Terminal {
       return message;
     }
     final StringBuffer buffer = StringBuffer();
-    final String colorCodes = _colorMap[color];
+    final String colorCodes = _colorMap[color]!;
     for (String line in message.split('\n')) {
       // If there were resets in the string before, then keep them, but
       // restart the color right after. This prevents embedded resets from
@@ -273,26 +269,23 @@ class AnsiTerminal implements Terminal {
   @override
   bool get stdinHasTerminal => _stdio.stdinHasTerminal;
 
-  Stream<String> _broadcastStdInString;
+  Stream<String>? _broadcastStdInString;
 
   @override
   Stream<String> get keystrokes {
-    _broadcastStdInString ??= _stdio.stdin.transform<String>(const AsciiDecoder(allowInvalid: true)).asBroadcastStream();
-    return _broadcastStdInString;
+    return _broadcastStdInString ??= _stdio.stdin.transform<String>(const AsciiDecoder(allowInvalid: true)).asBroadcastStream();
   }
 
   @override
   Future<String> promptForCharInput(
     List<String> acceptedCharacters, {
-    @required Logger logger,
-    String prompt,
-    int defaultChoiceIndex,
+    required Logger logger,
+    String? prompt,
+    int? defaultChoiceIndex,
     bool displayAcceptedCharacters = true,
   }) async {
-    assert(acceptedCharacters != null);
     assert(acceptedCharacters.isNotEmpty);
     assert(prompt == null || prompt.isNotEmpty);
-    assert(displayAcceptedCharacters != null);
     if (!usesTerminalUi) {
       throw StateError('cannot prompt without a terminal ui');
     }
@@ -303,7 +296,7 @@ class AnsiTerminal implements Terminal {
       charactersToDisplay[defaultChoiceIndex] = bolden(charactersToDisplay[defaultChoiceIndex]);
       acceptedCharacters.add('');
     }
-    String choice;
+    String? choice;
     singleCharMode = true;
     while (choice == null || choice.length > 1 || !acceptedCharacters.contains(choice)) {
       if (prompt != null) {
@@ -329,7 +322,7 @@ class _TestTerminal implements Terminal {
   _TestTerminal({this.supportsColor = false, this.supportsEmoji = false});
 
   @override
-  bool usesTerminalUi;
+  bool usesTerminalUi = false;
 
   @override
   String bolden(String message) => message;
@@ -345,9 +338,9 @@ class _TestTerminal implements Terminal {
 
   @override
   Future<String> promptForCharInput(List<String> acceptedCharacters, {
-    @required Logger logger,
-    String prompt,
-    int defaultChoiceIndex,
+    required Logger logger,
+    String? prompt,
+    int? defaultChoiceIndex,
     bool displayAcceptedCharacters = true,
   }) {
     throw UnsupportedError('promptForCharInput not supported in the test terminal.');