Fix crash on vswhere query on missing installations (#40786)

packages/flutter_tools/lib/src/windows/visual_studio_validator.dart

@@ -12,7 +12,9 @@ VisualStudioValidator get visualStudioValidator => context.get<VisualStudioValid
 class VisualStudioValidator extends DoctorValidator {
   const VisualStudioValidator() : super('Visual Studio - develop for Windows');
 
-  int get majorVersion => int.tryParse(visualStudio.fullVersion.split('.')[0]);
+  int get majorVersion => visualStudio.fullVersion != null
+      ? int.tryParse(visualStudio.fullVersion.split('.')[0])
+      : null;
 
   @override
   Future<ValidationResult> validate() async {

packages/flutter_tools/test/general.shard/windows/visual_studio_test.dart

@@ -35,20 +35,20 @@ void main() {
   // A minimum version of a response where a VS installation was found.
   const Map<String, dynamic> _defaultResponse = <String, dynamic>{
     'installationPath': visualStudioPath,
-    'displayName': 'Visual Studio Community 2017',
-    'installationVersion': '15.9.28307.665',
+    'displayName': 'Visual Studio Community 2019',
+    'installationVersion': '16.2.29306.81',
     'isRebootRequired': false,
     'isComplete': true,
     'isLaunchable': true,
     'isPrerelease': false,
     'catalog': <String, dynamic>{
-      'productDisplayVersion': '15.9.12',
-    },
+      'productDisplayVersion': '16.2.5',
+    }
   };
 
   // A version of a response that doesn't include certain installation status
   // information that might be missing in older Visual Studio versions.
-  const Map<String, dynamic> _oldResponse = <String, dynamic>{
+  const Map<String, dynamic> _missingStatusResponse = <String, dynamic>{
     'installationPath': visualStudioPath,
     'displayName': 'Visual Studio Community 2017',
     'installationVersion': '15.9.28307.665',
@@ -205,10 +205,32 @@ void main() {
       ProcessManager: () => mockProcessManager,
     });
 
+    testUsingContext('necessaryComponentDescriptions suggest the right VS tools on major version 15', () {
+
+      visualStudio = VisualStudio();
+      final String toolsString = visualStudio.necessaryComponentDescriptions(15)[1];
+      expect(toolsString.contains('v141'), true);
+    }, overrides: <Type, Generator>{
+      FileSystem: () => memoryFilesystem,
+      Platform: () => windowsPlatform,
+      ProcessManager: () => mockProcessManager,
+    });
+
+    testUsingContext('necessaryComponentDescriptions suggest the right VS tools on major version != 15', () {
+
+      visualStudio = VisualStudio();
+      final String toolsString = visualStudio.necessaryComponentDescriptions(16)[1];
+      expect(toolsString.contains('v142'), true);
+    }, overrides: <Type, Generator>{
+      FileSystem: () => memoryFilesystem,
+      Platform: () => windowsPlatform,
+      ProcessManager: () => mockProcessManager,
+    });
+
     testUsingContext('isInstalled returns true even with missing status information', () {
       setMockCompatibleVisualStudioInstallation(null);
       setMockPrereleaseVisualStudioInstallation(null);
-      setMockAnyVisualStudioInstallation(_oldResponse);
+      setMockAnyVisualStudioInstallation(_missingStatusResponse);
 
       visualStudio = VisualStudio();
       expect(visualStudio.isInstalled, true);
@@ -360,10 +382,10 @@ void main() {
       setMockAnyVisualStudioInstallation(_defaultResponse);
 
       visualStudio = VisualStudio();
-      expect(visualStudio.displayName, equals('Visual Studio Community 2017'));
-      expect(visualStudio.displayVersion, equals('15.9.12'));
+      expect(visualStudio.displayName, equals('Visual Studio Community 2019'));
+      expect(visualStudio.displayVersion, equals('16.2.5'));
       expect(visualStudio.installLocation, equals(visualStudioPath));
-      expect(visualStudio.fullVersion, equals('15.9.28307.665'));
+      expect(visualStudio.fullVersion, equals('16.2.29306.81'));
     }, overrides: <Type, Generator>{
       FileSystem: () => memoryFilesystem,
       Platform: () => windowsPlatform,
@@ -386,7 +408,17 @@ void main() {
     });
 
     testUsingContext('Metadata is for compatible version when latest is missing components', () {
-      setMockCompatibleVisualStudioInstallation(_defaultResponse);
+      // Return a different version for queries without the required packages.
+      final Map<String, dynamic> olderButCompleteVersionResponse = <String, dynamic>{
+        'installationPath': visualStudioPath,
+        'displayName': 'Visual Studio Community 2017',
+        'installationVersion': '15.9.28307.665',
+        'catalog': <String, dynamic>{
+          'productDisplayVersion': '15.9.12',
+        }
+      };
+
+      setMockCompatibleVisualStudioInstallation(olderButCompleteVersionResponse);
       setMockPrereleaseVisualStudioInstallation(null);
       // Return a different version for queries without the required packages.
       final Map<String, dynamic> incompleteVersionResponse = <String, dynamic>{

packages/flutter_tools/test/general.shard/windows/visual_studio_validator_test.dart

@@ -19,19 +19,35 @@ void main() {
 
     setUp(() {
       mockVisualStudio = MockVisualStudio();
-      // Mock a valid VS installation.
+      // Default values regardless of whether VS is installed or not.
+      when(mockVisualStudio.workloadDescription).thenReturn('Desktop development');
+      when(mockVisualStudio.necessaryComponentDescriptions(any)).thenReturn(<String>['A', 'B']);
+    });
+
+    // Assigns default values for a complete VS installation with necessary components.
+    void _configureMockVisualStudioAsInstalled() {
       when(mockVisualStudio.isInstalled).thenReturn(true);
       when(mockVisualStudio.isPrerelease).thenReturn(false);
       when(mockVisualStudio.isComplete).thenReturn(true);
       when(mockVisualStudio.isLaunchable).thenReturn(true);
       when(mockVisualStudio.isRebootRequired).thenReturn(false);
       when(mockVisualStudio.hasNecessaryComponents).thenReturn(true);
-      when(mockVisualStudio.workloadDescription).thenReturn('Desktop development');
-      when(mockVisualStudio.necessaryComponentDescriptions(any)).thenReturn(<String>['A', 'B']);
       when(mockVisualStudio.fullVersion).thenReturn('15.1');
-    });
+      when(mockVisualStudio.displayName).thenReturn('Visual Studio Community 2019');
+    }
+
+    // Assigns default values for a missing VS installation.
+    void _configureMockVisualStudioAsNotInstalled() {
+      when(mockVisualStudio.isInstalled).thenReturn(false);
+      when(mockVisualStudio.isPrerelease).thenReturn(false);
+      when(mockVisualStudio.isComplete).thenReturn(false);
+      when(mockVisualStudio.isLaunchable).thenReturn(false);
+      when(mockVisualStudio.isRebootRequired).thenReturn(false);
+      when(mockVisualStudio.hasNecessaryComponents).thenReturn(false);
+    }
 
     testUsingContext('Emits a message when Visual Studio is a pre-release version', () async {
+      _configureMockVisualStudioAsInstalled();
       when(visualStudio.isPrerelease).thenReturn(true);
 
       const VisualStudioValidator validator = VisualStudioValidator();
@@ -42,16 +58,8 @@ void main() {
       VisualStudio: () => mockVisualStudio,
     });
 
-    testUsingContext('Emits missing status when Visual Studio is not installed', () async {
-      when(visualStudio.isInstalled).thenReturn(false);
-      const VisualStudioValidator validator = VisualStudioValidator();
-      final ValidationResult result = await validator.validate();
-      expect(result.type, ValidationType.missing);
-    }, overrides: <Type, Generator>{
-      VisualStudio: () => mockVisualStudio,
-    });
-
     testUsingContext('Emits a partial status when Visual Studio installation is incomplete', () async {
+      _configureMockVisualStudioAsInstalled();
       when(visualStudio.isComplete).thenReturn(false);
 
       const VisualStudioValidator validator = VisualStudioValidator();
@@ -64,6 +72,7 @@ void main() {
     });
 
     testUsingContext('Emits a partial status when Visual Studio installation needs rebooting', () async {
+      _configureMockVisualStudioAsInstalled();
       when(visualStudio.isRebootRequired).thenReturn(true);
 
       const VisualStudioValidator validator = VisualStudioValidator();
@@ -76,6 +85,7 @@ void main() {
     });
 
     testUsingContext('Emits a partial status when Visual Studio installation is not launchable', () async {
+      _configureMockVisualStudioAsInstalled();
       when(visualStudio.isLaunchable).thenReturn(false);
 
       const VisualStudioValidator validator = VisualStudioValidator();
@@ -89,6 +99,7 @@ void main() {
 
 
     testUsingContext('Emits partial status when Visual Studio is installed without necessary components', () async {
+      _configureMockVisualStudioAsInstalled();
       when(visualStudio.hasNecessaryComponents).thenReturn(false);
       const VisualStudioValidator validator = VisualStudioValidator();
       final ValidationResult result = await validator.validate();
@@ -98,15 +109,19 @@ void main() {
     });
 
     testUsingContext('Emits installed status when Visual Studio is installed with necessary components', () async {
+      _configureMockVisualStudioAsInstalled();
       const VisualStudioValidator validator = VisualStudioValidator();
       final ValidationResult result = await validator.validate();
+      final ValidationMessage expectedDisplayNameMessage = ValidationMessage(
+        userMessages.visualStudioVersion(visualStudio.displayName, visualStudio.fullVersion));
+      expect(result.messages.contains(expectedDisplayNameMessage), true);
       expect(result.type, ValidationType.installed);
     }, overrides: <Type, Generator>{
       VisualStudio: () => mockVisualStudio,
     });
 
     testUsingContext('Emits missing status when Visual Studio is not installed', () async {
-      when(visualStudio.isInstalled).thenReturn(false);
+      _configureMockVisualStudioAsNotInstalled();
       const VisualStudioValidator validator = VisualStudioValidator();
       final ValidationResult result = await validator.validate();
       final ValidationMessage expectedMessage = ValidationMessage.error(