[flutter_tool,doctor] Fix and test gen_snapshot failure message (#27253)

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

@@ -19,7 +19,7 @@ class UserMessages {
   String get flutterBinariesLinuxRepairCommands =>
       'On Debian/Ubuntu/Mint: sudo apt-get install lib32stdc++6\n'
       'On Fedora: dnf install libstdc++.i686\n'
-      'On Arch: pacman -S lib32-libstdc++5';
+      'On Arch: pacman -S lib32-libstdc++5 (you need to enable multilib: https://wiki.archlinux.org/index.php/Official_repositories#multilib)';
 
   // Messages used in NoIdeValidator
   String get noIdeStatusInfo => 'No supported IDEs installed';

packages/flutter_tools/lib/src/doctor.dart

@@ -50,7 +50,7 @@ class _DefaultDoctorValidatorsProvider implements DoctorValidatorsProvider {
   List<DoctorValidator> get validators {
     if (_validators == null) {
       _validators = <DoctorValidator>[];
-      _validators.add(_FlutterValidator());
+      _validators.add(FlutterValidator());
 
       if (androidWorkflow.appliesToHostPlatform)
         _validators.add(GroupedValidator(<DoctorValidator>[androidValidator, androidLicenseValidator]));
@@ -438,8 +438,8 @@ class ValidationMessage {
   String toString() => message;
 }
 
-class _FlutterValidator extends DoctorValidator {
-  _FlutterValidator() : super('Flutter');
+class FlutterValidator extends DoctorValidator {
+  FlutterValidator() : super('Flutter');
 
   @override
   Future<ValidationResult> validate() async {

packages/flutter_tools/test/commands/doctor_test.dart

@@ -4,10 +4,17 @@
 
 import 'dart:async';
 
+import 'package:mockito/mockito.dart';
+import 'package:process/process.dart';
+
+import 'package:flutter_tools/src/artifacts.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
+import 'package:flutter_tools/src/base/io.dart';
 import 'package:flutter_tools/src/base/platform.dart';
 import 'package:flutter_tools/src/base/terminal.dart';
+import 'package:flutter_tools/src/base/user_messages.dart';
 import 'package:flutter_tools/src/doctor.dart';
+import 'package:flutter_tools/src/globals.dart';
 import 'package:flutter_tools/src/proxy_validator.dart';
 import 'package:flutter_tools/src/vscode/vscode.dart';
 import 'package:flutter_tools/src/vscode/vscode_validator.dart';
@@ -21,6 +28,12 @@ final Map<Type, Generator> noColorTerminalOverride = <Type, Generator>{
 };
 
 void main() {
+  MockProcessManager mockProcessManager;
+
+  setUp(() {
+    mockProcessManager = MockProcessManager();
+  });
+
   group('doctor', () {
     testUsingContext('intellij validator', () async {
       const String installPath = '/path/to/intelliJ';
@@ -290,6 +303,29 @@ void main() {
               '! Doctor found issues in 4 categories.\n'
       ));
     }, overrides: noColorTerminalOverride);
+
+    testUsingContext('gen_snapshot does not work', () async {
+      when(mockProcessManager.runSync(
+        <String>[artifacts.getArtifactPath(Artifact.genSnapshot)],
+        workingDirectory: anyNamed('workingDirectory'),
+        environment: anyNamed('environment'),
+      )).thenReturn(ProcessResult(101, 1, '', ''));
+
+      expect(await FlutterValidatorDoctor().diagnose(verbose: false), isTrue);
+      final List<String> statusLines = testLogger.statusText.split('\n');
+      for (String msg in userMessages.flutterBinariesDoNotRun.split('\n')) {
+        expect(statusLines, contains(contains(msg)));
+      }
+      if (platform.isLinux) {
+        for (String msg in userMessages.flutterBinariesLinuxRepairCommands.split('\n')) {
+          expect(statusLines, contains(contains(msg)));
+        }
+      }
+    }, overrides: <Type, Generator>{
+      OutputPreferences: () => OutputPreferences(wrapText: false),
+      ProcessManager: () => mockProcessManager,
+      Platform: _kNoColorOutputPlatform,
+    });
   });
 
   testUsingContext('validate non-verbose output wrapping', () async {
@@ -687,6 +723,15 @@ class FakeGroupedDoctorWithStatus extends Doctor {
   }
 }
 
+class FlutterValidatorDoctor extends Doctor {
+  List<DoctorValidator> _validators;
+  @override
+  List<DoctorValidator> get validators {
+    _validators ??= <DoctorValidator>[FlutterValidator()];
+    return _validators;
+  }
+}
+
 /// A doctor that takes any two validators. Used to check behavior when
 /// merging ValidationTypes (installed, missing, partial).
 class FakeSmallGroupDoctor extends Doctor {
@@ -717,3 +762,5 @@ class VsCodeValidatorTestTargets extends VsCodeValidator {
   static final String validExtensions = fs.path.join('test', 'data', 'vscode', 'extensions');
   static final String missingExtensions = fs.path.join('test', 'data', 'vscode', 'notExtensions');
 }
+
+class MockProcessManager extends Mock implements ProcessManager {}