Handle ProcessExceptions due to git missing on the host (#154445)

Fixes https://github.com/flutter/flutter/issues/133585.

This PR elects to add a new catch within `_handleToolError` that checks any uncaught error. This new catch will exit the tool without crashing provided the following conditions are met:

1. the error is a `ProcessException`,
2. the error message contains `git` somewhere in the message (we don't match on the entire string in case it changes or is locale-dependent), and
3. `git` does not appear to be runnable on the host system (`ProcessManager.canRun` returns `false` for git).

This is preferable to checking for runnability of `git` before we run it for 1) its simplicity and 2) lack of performance penalty for users that already have git installed (almost every single one).

This PR also does some light refactoring to runner_test.dart to make room for tests that aren't related to crash reporting.

packages/flutter_tools/lib/runner.dart

@@ -7,6 +7,7 @@ import 'dart:async';
 import 'package:args/command_runner.dart';
 import 'package:intl/intl.dart' as intl;
 import 'package:intl/intl_standalone.dart' as intl_standalone;
+import 'package:process/process.dart';
 import 'package:unified_analytics/unified_analytics.dart';
 
 import 'src/base/async_guard.dart';
@@ -185,6 +186,16 @@ Future<int> _handleToolError(
     } else {
       return exitWithHooks(error.exitCode, shutdownHooks: shutdownHooks);
     }
+  } else if (error is ProcessException &&
+      _isErrorDueToGitMissing(error, globals.processManager, globals.logger)) {
+    globals.printError('${error.message}\n');
+    globals.printError(
+      'An error was encountered when trying to run git.\n'
+      "Please ensure git is installed and available in your system's search path. "
+      'See https://docs.flutter.dev/get-started/install for instructions on '
+      'installing git for your platform.',
+    );
+    return exitWithHooks(1, shutdownHooks: shutdownHooks);
   } else {
     // We've crashed; emit a log report.
     globals.stdio.stderrWrite('\n');
@@ -301,3 +312,22 @@ Future<File> _createLocalCrashReport(CrashDetails details) async {
 
   return crashFile;
 }
+
+bool _isErrorDueToGitMissing(
+  ProcessException exception,
+  ProcessManager processManager,
+  Logger logger,
+) {
+  if (!exception.message.contains('git')) {
+    return false;
+  }
+
+  try {
+    return !processManager.canRun('git');
+  } on Object catch (error) {
+    logger.printTrace(
+      'Unable to check whether git is runnable: $error\n'
+    );
+    return true;
+  }
+}

packages/flutter_tools/lib/src/web/chrome.dart

@@ -578,7 +578,7 @@ Future<ChromeTab?> getChromeTabGuarded(
   void Function(Object error, StackTrace stackTrace)? onIoError,
 }) async {
   try {
-    return asyncGuard(
+    return await asyncGuard(
       () => chromeConnection.getTab(
         accept,
         retryFor: retryFor,

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

@@ -10,6 +10,7 @@ import 'package:flutter_tools/src/artifacts.dart';
 import 'package:flutter_tools/src/base/bot_detector.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/io.dart' as io;
+import 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/base/net.dart';
 import 'package:flutter_tools/src/base/platform.dart';
 import 'package:flutter_tools/src/base/process.dart';
@@ -19,6 +20,7 @@ import 'package:flutter_tools/src/globals.dart' as globals;
 import 'package:flutter_tools/src/reporting/crash_reporting.dart';
 import 'package:flutter_tools/src/reporting/reporting.dart';
 import 'package:flutter_tools/src/runner/flutter_command.dart';
+import 'package:test/fake.dart';
 import 'package:unified_analytics/unified_analytics.dart';
 
 import '../../src/common.dart';
@@ -29,12 +31,10 @@ import '../../src/fakes.dart';
 const String kCustomBugInstructions = 'These are instructions to report with a custom bug tracker.';
 
 void main() {
-  int? firstExitCode;
-  late MemoryFileSystem fileSystem;
-
-  group('runner', () {
+  group('runner (crash reporting)', () {
+    int? firstExitCode;
+    late MemoryFileSystem fileSystem;
     late FakeAnalytics fakeAnalytics;
-    late TestUsage testUsage;
 
     setUp(() {
       // Instead of exiting with dart:io exit(), this causes an exception to
@@ -59,8 +59,6 @@ void main() {
         fs: fileSystem,
         fakeFlutterVersion: FakeFlutterVersion(),
       );
-
-      testUsage = TestUsage();
     });
 
     tearDown(() {
@@ -327,10 +325,84 @@ void main() {
         HttpClientFactory: () => () => FakeHttpClient.any(),
       });
     });
+  });
+
+  group('runner', () {
+    late MemoryFileSystem fs;
+
+    setUp(() {
+      io.setExitFunctionForTests((int exitCode) {});
+
+      fs = MemoryFileSystem.test();
+
+      Cache.disableLocking();
+    });
+
+    tearDown(() {
+      io.restoreExitFunction();
+      Cache.enableLocking();
+    });
+
+    testUsingContext("catches ProcessException calling git because it's not available", () async {
+      final _GitNotFoundFlutterCommand command = _GitNotFoundFlutterCommand();
+
+      await runner.run(
+        <String>[command.name],
+        () => <FlutterCommand>[
+          command,
+        ],
+        // This flutterVersion disables crash reporting.
+        flutterVersion: '[user-branch]/',
+        reportCrashes: false,
+        shutdownHooks: ShutdownHooks(),
+      );
+
+      expect(
+          (globals.logger as BufferLogger).errorText,
+          'Failed to find "git" in the search path.\n'
+          '\n'
+          'An error was encountered when trying to run git.\n'
+          "Please ensure git is installed and available in your system's search path. "
+          'See https://docs.flutter.dev/get-started/install for instructions on installing git for your platform.\n');
+      },
+      overrides: <Type, Generator>{
+        FileSystem: () => fs,
+        Artifacts: () => Artifacts.test(),
+        ProcessManager: () =>
+            FakeProcessManager.any()..excludedExecutables.add('git'),
+      },
+    );
+
+    testUsingContext('handles ProcessException calling git when ProcessManager.canRun fails', () async {
+      final _GitNotFoundFlutterCommand command = _GitNotFoundFlutterCommand();
+
+      await runner.run(
+        <String>[command.name],
+        () => <FlutterCommand>[
+          command,
+        ],
+        // This flutterVersion disables crash reporting.
+        flutterVersion: '[user-branch]/',
+        reportCrashes: false,
+        shutdownHooks: ShutdownHooks(),
+      );
+
+      expect(
+          (globals.logger as BufferLogger).errorText,
+          'Failed to find "git" in the search path.\n'
+          '\n'
+          'An error was encountered when trying to run git.\n'
+          "Please ensure git is installed and available in your system's search path. "
+          'See https://docs.flutter.dev/get-started/install for instructions on installing git for your platform.\n');
+      },
+      overrides: <Type, Generator>{
+        FileSystem: () => fs,
+        Artifacts: () => Artifacts.test(),
+        ProcessManager: () => _ErrorOnCanRunFakeProcessManager(),
+      },
+    );
 
     testUsingContext('do not print welcome on bots', () async {
-        io.setExitFunctionForTests((int exitCode) {});
-
         await runner.run(
           <String>['--version', '--machine'],
           () => <FlutterCommand>[],
@@ -339,13 +411,13 @@ void main() {
           shutdownHooks: ShutdownHooks(),
         );
 
-        expect(testUsage.printedWelcome, false);
+        expect((globals.flutterUsage as TestUsage).printedWelcome, false);
       },
       overrides: <Type, Generator>{
         FileSystem: () => MemoryFileSystem.test(),
         ProcessManager: () => FakeProcessManager.any(),
         BotDetector: () => const FakeBotDetector(true),
-        Usage: () => testUsage,
+        Usage: () => TestUsage(),
       },
     );
   });
@@ -570,6 +642,23 @@ class CrashingFlutterCommand extends FlutterCommand {
   }
 }
 
+class _GitNotFoundFlutterCommand extends FlutterCommand {
+  @override
+  String get description => '';
+
+  @override
+  String get name => 'git-not-found';
+
+  @override
+  Future<FlutterCommandResult> runCommand() {
+    throw const io.ProcessException(
+      'git',
+      <String>['log'],
+      'Failed to find "git" in the search path.',
+    );
+  }
+}
+
 class CrashingUsage implements Usage {
   CrashingUsage() : _impl = Usage(
     versionOverride: '[user-branch]',
@@ -670,3 +759,14 @@ class WaitingCrashReporter implements CrashReporter {
     return _future;
   }
 }
+
+class _ErrorOnCanRunFakeProcessManager extends Fake implements FakeProcessManager {
+  final FakeProcessManager delegate = FakeProcessManager.any();
+  @override
+  bool canRun(dynamic executable, {String? workingDirectory}) {
+    if (executable == 'git') {
+      throw Exception("oh no, we couldn't check for git!");
+    }
+    return delegate.canRun(executable, workingDirectory: workingDirectory);
+  }
+}