Migrate tools chrome to null safety (#79801)

packages/flutter_tools/lib/src/web/chrome.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';
@@ -56,7 +54,7 @@ typedef BrowserFinder = String Function(Platform, FileSystem);
 /// Does not verify whether the executable exists.
 String findChromeExecutable(Platform platform, FileSystem fileSystem) {
   if (platform.environment.containsKey(kChromeEnvironment)) {
-    return platform.environment[kChromeEnvironment];
+    return platform.environment[kChromeEnvironment]!;
   }
   if (platform.isLinux) {
     return kLinuxExecutable;
@@ -67,9 +65,12 @@ String findChromeExecutable(Platform platform, FileSystem fileSystem) {
   if (platform.isWindows) {
     /// The possible locations where the chrome executable can be located on windows.
     final List<String> kWindowsPrefixes = <String>[
-      platform.environment['LOCALAPPDATA'],
-      platform.environment['PROGRAMFILES'],
-      platform.environment['PROGRAMFILES(X86)'],
+      if (platform.environment.containsKey('LOCALAPPDATA'))
+        platform.environment['LOCALAPPDATA']!,
+      if (platform.environment.containsKey('PROGRAMFILES'))
+        platform.environment['PROGRAMFILES']!,
+      if (platform.environment.containsKey('PROGRAMFILES(X86)'))
+        platform.environment['PROGRAMFILES(X86)']!,
     ];
     final String windowsPrefix = kWindowsPrefixes.firstWhere((String prefix) {
       if (prefix == null) {
@@ -88,14 +89,17 @@ String findChromeExecutable(Platform platform, FileSystem fileSystem) {
 /// Does not verify whether the executable exists.
 String findEdgeExecutable(Platform platform, FileSystem fileSystem) {
   if (platform.environment.containsKey(kEdgeEnvironment)) {
-    return platform.environment[kEdgeEnvironment];
+    return platform.environment[kEdgeEnvironment]!;
   }
   if (platform.isWindows) {
     /// The possible locations where the Edge executable can be located on windows.
     final List<String> kWindowsPrefixes = <String>[
-      platform.environment['LOCALAPPDATA'],
-      platform.environment['PROGRAMFILES'],
-      platform.environment['PROGRAMFILES(X86)'],
+      if (platform.environment.containsKey('LOCALAPPDATA'))
+        platform.environment['LOCALAPPDATA']!,
+      if (platform.environment.containsKey('PROGRAMFILES'))
+        platform.environment['PROGRAMFILES']!,
+      if (platform.environment.containsKey('PROGRAMFILES(X86)'))
+        platform.environment['PROGRAMFILES(X86)']!,
     ];
     final String windowsPrefix = kWindowsPrefixes.firstWhere((String prefix) {
       if (prefix == null) {
@@ -113,12 +117,12 @@ String findEdgeExecutable(Platform platform, FileSystem fileSystem) {
 /// A launcher for Chromium browsers with devtools configured.
 class ChromiumLauncher {
   ChromiumLauncher({
-    @required FileSystem fileSystem,
-    @required Platform platform,
-    @required ProcessManager processManager,
-    @required OperatingSystemUtils operatingSystemUtils,
-    @required BrowserFinder browserFinder,
-    @required Logger logger,
+    required FileSystem fileSystem,
+    required Platform platform,
+    required ProcessManager processManager,
+    required OperatingSystemUtils operatingSystemUtils,
+    required BrowserFinder browserFinder,
+    required Logger logger,
   }) : _fileSystem = fileSystem,
        _platform = platform,
        _processManager = processManager,
@@ -162,9 +166,9 @@ class ChromiumLauncher {
   /// [skipCheck] does not attempt to make a devtools connection before returning.
   Future<Chromium> launch(String url, {
     bool headless = false,
-    int debugPort,
+    int? debugPort,
     bool skipCheck = false,
-    Directory cacheDir,
+    Directory? cacheDir,
   }) async {
     if (currentCompleter.isCompleted) {
       throwToolExit('Only one instance of chrome can be started.');
@@ -214,10 +218,10 @@ class ChromiumLauncher {
       url,
     ];
 
-    final Process process = await _spawnChromiumProcess(args);
+    final Process? process = await _spawnChromiumProcess(args);
 
     // When the process exits, copy the user settings back to the provided data-dir.
-    if (cacheDir != null) {
+    if (process != null && cacheDir != null) {
       unawaited(process.exitCode.whenComplete(() {
         _cacheUserSessionInformation(userDataDir, cacheDir);
       }));
@@ -231,7 +235,7 @@ class ChromiumLauncher {
     ), skipCheck);
   }
 
-  Future<Process> _spawnChromiumProcess(List<String> args) async {
+  Future<Process?> _spawnChromiumProcess(List<String> args) async {
     // Keep attempting to launch the browser until one of:
     // - Chrome launched successfully, in which case we just return from the loop.
     // - The tool detected an unretriable Chrome error, in which case we throw ToolExit.
@@ -264,7 +268,8 @@ class ChromiumLauncher {
               'Encountered glibc bug https://sourceware.org/bugzilla/show_bug.cgi?id=19329. '
               'Will try launching browser again.',
             );
-            return null;
+            // Return value unused.
+            return '';
           }
           _logger.printTrace('Failed to launch browser. Command used to launch it: ${args.join(' ')}');
           throw ToolExit(
@@ -283,7 +288,8 @@ class ChromiumLauncher {
       // launching more processes.
       unawaited(process.exitCode.timeout(const Duration(seconds: 1), onTimeout: () {
         process.kill();
-        return null;
+        // sigterm
+        return 15;
       }));
     }
   }
@@ -302,7 +308,7 @@ class ChromiumLauncher {
   /// Note: more detailed docs of the Chrome user preferences store exists here:
   /// https://www.chromium.org/developers/design-documents/preferences.
   void _cacheUserSessionInformation(Directory userDataDir, Directory cacheDir) {
-    final Directory targetChromeDefault = _fileSystem.directory(_fileSystem.path.join(cacheDir?.path ?? '', _chromeDefaultPath));
+    final Directory targetChromeDefault = _fileSystem.directory(_fileSystem.path.join(cacheDir.path, _chromeDefaultPath));
     final Directory sourceChromeDefault = _fileSystem.directory(_fileSystem.path.join(userDataDir.path, _chromeDefaultPath));
     if (sourceChromeDefault.existsSync()) {
       targetChromeDefault.createSync(recursive: true);
@@ -315,7 +321,7 @@ class ChromiumLauncher {
       }
     }
 
-    final File targetPreferencesFile = _fileSystem.file(_fileSystem.path.join(cacheDir?.path ?? '', _preferencesPath));
+    final File targetPreferencesFile = _fileSystem.file(_fileSystem.path.join(cacheDir.path, _preferencesPath));
     final File sourcePreferencesFile = _fileSystem.file(_fileSystem.path.join(userDataDir.path, _preferencesPath));
 
     if (sourcePreferencesFile.existsSync()) {
@@ -330,7 +336,7 @@ class ChromiumLauncher {
   /// Restore Chrome user information from a per-project cache into Chrome's
   /// user data directory.
   void _restoreUserSessionInformation(Directory cacheDir, Directory userDataDir) {
-    final Directory sourceChromeDefault = _fileSystem.directory(_fileSystem.path.join(cacheDir.path ?? '', _chromeDefaultPath));
+    final Directory sourceChromeDefault = _fileSystem.directory(_fileSystem.path.join(cacheDir.path, _chromeDefaultPath));
     final Directory targetChromeDefault = _fileSystem.directory(_fileSystem.path.join(userDataDir.path, _chromeDefaultPath));
     try {
       if (sourceChromeDefault.existsSync()) {
@@ -367,18 +373,18 @@ class Chromium {
     this.debugPort,
     this.chromeConnection, {
     this.url,
-    Process process,
-    @required ChromiumLauncher chromiumLauncher,
+    Process? process,
+    required ChromiumLauncher chromiumLauncher,
   })  : _process = process,
         _chromiumLauncher = chromiumLauncher;
 
-  final String url;
+  final String? url;
   final int debugPort;
-  final Process _process;
+  final Process? _process;
   final ChromeConnection chromeConnection;
   final ChromiumLauncher _chromiumLauncher;
 
-  Future<int> get onExit => _process.exitCode;
+  Future<int?> get onExit async => _process?.exitCode;
 
   Future<void> close() async {
     if (_chromiumLauncher.hasChromeInstance) {