Refactor vswhere.exe integration (#104133)

`VisualStudio` calls `vswhere.exe` to find Visual Studio installations and determine if they satisfy Flutter's requirements. Previously, `VisualStudio` stored the JSON output from `vswhere.exe` as `Map`s, resulting in duplicated logic to read the JSON output (once to validate values, second to expose values). Also, `VisualStudio` stored two copies of the JSON output (the latest valid installation as well as the latest VS installation).

This change simplifies `VisualStudio` by introducing a new `VswhereDetails`. This type contains the logic to read `vswhere.exe`'s JSON output, and, understand whether an installation is usable by Flutter. In the future, this `VswhereDetails` type will be used to make Flutter doctor resilient to bad UTF-8 output from `vswhere.exe`.

Part of https://github.com/flutter/flutter/issues/102451.

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

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:meta/meta.dart';
 import 'package:process/process.dart';
 
 import '../base/common.dart';
@@ -33,7 +34,7 @@ class VisualStudio {
   /// Versions older than 2017 Update 2 won't be detected, so error messages to
   /// users should take into account that [false] may mean that the user may
   /// have an old version rather than no installation at all.
-  bool get isInstalled => _bestVisualStudioDetails.isNotEmpty;
+  bool get isInstalled => _bestVisualStudioDetails != null;
 
   bool get isAtLeastMinimumVersion {
     final int? installedMajorVersion = _majorVersion;
@@ -42,30 +43,25 @@ class VisualStudio {
 
   /// True if there is a version of Visual Studio with all the components
   /// necessary to build the project.
-  bool get hasNecessaryComponents => _usableVisualStudioDetails.isNotEmpty;
+  bool get hasNecessaryComponents => _bestVisualStudioDetails?.isUsable ?? false;
 
   /// The name of the Visual Studio install.
   ///
   /// For instance: "Visual Studio Community 2019".
-  String? get displayName => _bestVisualStudioDetails[_displayNameKey] as String?;
+  String? get displayName => _bestVisualStudioDetails?.displayName;
 
   /// The user-friendly version number of the Visual Studio install.
   ///
   /// For instance: "15.4.0".
-  String? get displayVersion {
-    if (_bestVisualStudioDetails[_catalogKey] == null) {
-      return null;
-    }
-    return (_bestVisualStudioDetails[_catalogKey] as Map<String, dynamic>)[_catalogDisplayVersionKey] as String?;
-  }
+  String? get displayVersion => _bestVisualStudioDetails?.catalogDisplayVersion;
 
   /// The directory where Visual Studio is installed.
-  String? get installLocation => _bestVisualStudioDetails[_installationPathKey] as String?;
+  String? get installLocation => _bestVisualStudioDetails?.installationPath;
 
   /// The full version of the Visual Studio install.
   ///
   /// For instance: "15.4.27004.2002".
-  String? get fullVersion => _bestVisualStudioDetails[_fullVersionKey] as String?;
+  String? get fullVersion => _bestVisualStudioDetails?.fullVersion;
 
   // Properties that determine the status of the installation. There might be
   // Visual Studio versions that don't include them, so default to a "valid" value to
@@ -75,27 +71,27 @@ class VisualStudio {
   ///
   /// False if installation is not found.
   bool get isComplete {
-    if (_bestVisualStudioDetails.isEmpty) {
+    if (_bestVisualStudioDetails == null) {
       return false;
     }
-    return _bestVisualStudioDetails[_isCompleteKey] as bool? ?? true;
+    return _bestVisualStudioDetails!.isComplete ?? true;
   }
 
   /// True if Visual Studio is launchable.
   ///
   /// False if installation is not found.
   bool get isLaunchable {
-    if (_bestVisualStudioDetails.isEmpty) {
+    if (_bestVisualStudioDetails == null) {
       return false;
     }
-    return _bestVisualStudioDetails[_isLaunchableKey] as bool? ?? true;
+    return _bestVisualStudioDetails!.isLaunchable ?? true;
   }
 
-  /// True if the Visual Studio installation is as pre-release version.
-  bool get isPrerelease => _bestVisualStudioDetails[_isPrereleaseKey] as bool? ?? false;
+  /// True if the Visual Studio installation is a pre-release version.
+  bool get isPrerelease => _bestVisualStudioDetails?.isPrerelease ?? false;
 
   /// True if a reboot is required to complete the Visual Studio installation.
-  bool get isRebootRequired => _bestVisualStudioDetails[_isRebootRequiredKey] as bool? ?? false;
+  bool get isRebootRequired => _bestVisualStudioDetails?.isRebootRequired ?? false;
 
   /// The name of the recommended Visual Studio installer workload.
   String get workloadDescription => 'Desktop development with C++';
@@ -150,12 +146,13 @@ class VisualStudio {
   /// The path to CMake, or null if no Visual Studio installation has
   /// the components necessary to build.
   String? get cmakePath {
-    final Map<String, dynamic> details = _usableVisualStudioDetails;
-    if (details.isEmpty || _usableVisualStudioDetails[_installationPathKey] == null) {
+    final VswhereDetails? details = _bestVisualStudioDetails;
+    if (details == null || !details.isUsable || details.installationPath == null) {
       return null;
     }
+
     return _fileSystem.path.joinAll(<String>[
-      _usableVisualStudioDetails[_installationPathKey] as String,
+      details.installationPath!,
       'Common7',
       'IDE',
       'CommonExtensions',
@@ -253,33 +250,6 @@ class VisualStudio {
   /// vswhere argument to allow prerelease versions.
   static const String _vswherePrereleaseArgument = '-prerelease';
 
-  // Keys in a VS details dictionary returned from vswhere.
-
-  /// The root directory of the Visual Studio installation.
-  static const String _installationPathKey = 'installationPath';
-
-  /// The user-friendly name of the installation.
-  static const String _displayNameKey = 'displayName';
-
-  /// The complete version.
-  static const String _fullVersionKey = 'installationVersion';
-
-  /// Keys for the status of the installation.
-  static const String _isCompleteKey = 'isComplete';
-  static const String _isLaunchableKey = 'isLaunchable';
-  static const String _isRebootRequiredKey = 'isRebootRequired';
-
-  /// The 'catalog' entry containing more details.
-  static const String _catalogKey = 'catalog';
-
-  /// The key for a pre-release version.
-  static const String _isPrereleaseKey = 'isPrerelease';
-
-  /// The user-friendly version.
-  ///
-  /// This key is under the 'catalog' entry.
-  static const String _catalogDisplayVersionKey = 'productDisplayVersion';
-
   /// The registry path for Windows 10 SDK installation details.
   static const String _windows10SdkRegistryPath = r'HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Microsoft SDKs\Windows\v10.0';
 
@@ -287,10 +257,11 @@ class VisualStudio {
   /// SDKs are installed.
   static const String _windows10SdkRegistryKey = 'InstallationFolder';
 
-  /// Returns the details dictionary for the newest version of Visual Studio.
+  /// Returns the details of the newest version of Visual Studio.
+  ///
   /// If [validateRequirements] is set, the search will be limited to versions
   /// that have all of the required workloads and components.
-  Map<String, dynamic>? _visualStudioDetails({
+  VswhereDetails? _visualStudioDetails({
       bool validateRequirements = false,
       List<String>? additionalArguments,
       String? requiredWorkload
@@ -321,7 +292,7 @@ class VisualStudio {
         final List<Map<String, dynamic>> installations =
             (json.decode(whereResult.stdout) as List<dynamic>).cast<Map<String, dynamic>>();
         if (installations.isNotEmpty) {
-          return installations[0];
+          return VswhereDetails.fromJson(validateRequirements, installations[0]);
         }
       }
     } on ArgumentError {
@@ -334,90 +305,39 @@ class VisualStudio {
     return null;
   }
 
-  /// Checks if the given installation has issues that the user must resolve.
-  ///
-  /// Returns false if the required information is missing since older versions
-  /// of Visual Studio might not include them.
-  bool installationHasIssues(Map<String, dynamic>installationDetails) {
-    assert(installationDetails != null);
-    if (installationDetails[_isCompleteKey] != null && !(installationDetails[_isCompleteKey] as bool)) {
-      return true;
-    }
-
-    if (installationDetails[_isLaunchableKey] != null && !(installationDetails[_isLaunchableKey] as bool)) {
-      return true;
-    }
-
-    if (installationDetails[_isRebootRequiredKey] != null && installationDetails[_isRebootRequiredKey] as bool) {
-      return true;
-    }
-
-    return false;
-  }
-
-  /// Returns the details dictionary for the latest version of Visual Studio
-  /// that has all required components and is a supported version, or {} if
-  /// there is no such installation.
+  /// Returns the details of the best available version of Visual Studio.
   ///
-  /// If no installation is found, the cached VS details are set to an empty map
-  /// to avoid repeating vswhere queries that have already not found an installation.
-  late final Map<String, dynamic> _usableVisualStudioDetails = (){
+  /// If there's a version that has all the required components, that
+  /// will be returned, otherwise returns the latest installed version regardless
+  /// of components and version, or null if no such installation is found.
+  late final VswhereDetails?  _bestVisualStudioDetails = () {
+    // First, attempt to find the latest version of Visual Studio that satifies
+    // both the minimum supported version and the required workloads.
+    // Check in the order of stable VS, stable BT, pre-release VS, pre-release BT.
     final List<String> minimumVersionArguments = <String>[
       _vswhereMinVersionArgument,
       _minimumSupportedVersion.toString(),
     ];
-    Map<String, dynamic>? visualStudioDetails;
-    // Check in the order of stable VS, stable BT, pre-release VS, pre-release BT
     for (final bool checkForPrerelease in <bool>[false, true]) {
       for (final String requiredWorkload in _requiredWorkloads) {
-        visualStudioDetails ??= _visualStudioDetails(
+        final VswhereDetails? result = _visualStudioDetails(
           validateRequirements: true,
           additionalArguments: checkForPrerelease
               ? <String>[...minimumVersionArguments, _vswherePrereleaseArgument]
               : minimumVersionArguments,
           requiredWorkload: requiredWorkload);
-      }
-    }
 
-    Map<String, dynamic>? usableVisualStudioDetails;
-    if (visualStudioDetails != null) {
-      if (installationHasIssues(visualStudioDetails)) {
-        _cachedAnyVisualStudioDetails = visualStudioDetails;
-      } else {
-        usableVisualStudioDetails = visualStudioDetails;
+          if (result != null) {
+            return result;
+          }
       }
     }
-    return usableVisualStudioDetails ?? <String, dynamic>{};
-  }();
 
-  /// Returns the details dictionary of the latest version of Visual Studio,
-  /// regardless of components and version, or {} if no such installation is
-  /// found.
-  ///
-  /// If no installation is found, the cached VS details are set to an empty map
-  /// to avoid repeating vswhere queries that have already not found an
-  /// installation.
-  Map<String, dynamic>? _cachedAnyVisualStudioDetails;
-  Map<String, dynamic> get _anyVisualStudioDetails {
-    // Search for all types of installations.
-    _cachedAnyVisualStudioDetails ??= _visualStudioDetails(
+    // An installation that satifies requirements could not be found.
+    // Fallback to the latest Visual Studio installation.
+    return _visualStudioDetails(
         additionalArguments: <String>[_vswherePrereleaseArgument, '-all']);
-    // Add a sentinel empty value to avoid querying vswhere again.
-    _cachedAnyVisualStudioDetails ??= <String, dynamic>{};
-    return _cachedAnyVisualStudioDetails!;
-  }
-
-  /// Returns the details dictionary of the best available version of Visual
-  /// Studio.
-  ///
-  /// If there's a version that has all the required components, that
-  /// will be returned, otherwise returns the latest installed version (if any).
-  Map<String, dynamic> get _bestVisualStudioDetails {
-    if (_usableVisualStudioDetails.isNotEmpty) {
-      return _usableVisualStudioDetails;
-    }
-    return _anyVisualStudioDetails;
-  }
+  }();
 
   /// Returns the installation location of the Windows 10 SDKs, or null if the
   /// registry doesn't contain that information.
@@ -471,3 +391,87 @@ class VisualStudio {
     return highestVersion == null ? null : '10.$highestVersion';
   }
 }
+
+/// The details of a Visual Studio installation according to vswhere.
+@visibleForTesting
+class VswhereDetails {
+  const VswhereDetails({
+    required this.meetsRequirements,
+    required this.installationPath,
+    required this.displayName,
+    required this.fullVersion,
+    required this.isComplete,
+    required this.isLaunchable,
+    required this.isRebootRequired,
+    required this.isPrerelease,
+    required this.catalogDisplayVersion,
+  });
+
+  /// Create a `VswhereDetails` from the JSON output of vswhere.exe.
+  factory VswhereDetails.fromJson(
+    bool meetsRequirements,
+    Map<String, dynamic> details
+  ) {
+    final Map<String, dynamic>? catalog = details['catalog'] as Map<String, dynamic>?;
+
+    return VswhereDetails(
+      meetsRequirements: meetsRequirements,
+      installationPath: details['installationPath'] as String?,
+      displayName: details['displayName'] as String?,
+      fullVersion: details['installationVersion'] as String?,
+      isComplete: details['isComplete'] as bool?,
+      isLaunchable: details['isLaunchable'] as bool?,
+      isRebootRequired: details['isRebootRequired'] as bool?,
+      isPrerelease: details['isPrerelease'] as bool?,
+      catalogDisplayVersion: catalog == null ? null : catalog['productDisplayVersion'] as String?,
+    );
+  }
+
+  /// Whether the installation satisfies the required workloads and minimum version.
+  final bool meetsRequirements;
+
+  /// The root directory of the Visual Studio installation.
+  final String? installationPath;
+
+  /// The user-friendly name of the installation.
+  final String? displayName;
+
+  /// The complete version.
+  final String? fullVersion;
+
+  /// Keys for the status of the installation.
+  final bool? isComplete;
+  final bool? isLaunchable;
+  final bool? isRebootRequired;
+
+  /// The key for a pre-release version.
+  final bool? isPrerelease;
+
+  /// The user-friendly version.
+  final String? catalogDisplayVersion;
+
+  /// Checks if the Visual Studio installation can be used by Flutter.
+  ///
+  /// Returns false if the installation has issues the user must resolve.
+  /// This may return true even if required information is missing as older
+  /// versions of Visual Studio might not include them.
+  bool get isUsable {
+    if (!meetsRequirements) {
+      return false;
+    }
+
+    if (!(isComplete ?? true)) {
+      return false;
+    }
+
+    if (!(isLaunchable ?? true)) {
+      return false;
+    }
+
+    if (isRebootRequired ?? false) {
+      return false;
+    }
+
+    return true;
+  }
+}

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

@@ -863,6 +863,98 @@ void main() {
       expect(visualStudio.getWindows10SDKVersion(), null);
     });
   });
+
+  group(VswhereDetails, () {
+      test('Accepts empty JSON', () {
+        const bool meetsRequirements = true;
+        final Map<String, dynamic> json = <String, dynamic>{};
+
+        final VswhereDetails result = VswhereDetails.fromJson(meetsRequirements, json);
+
+        expect(result.installationPath, null);
+        expect(result.displayName, null);
+        expect(result.fullVersion, null);
+        expect(result.isComplete, null);
+        expect(result.isLaunchable, null);
+        expect(result.isRebootRequired, null);
+        expect(result.isPrerelease, null);
+        expect(result.catalogDisplayVersion, null);
+        expect(result.isUsable, isTrue);
+      });
+
+      test('Ignores unknown JSON properties', () {
+        const bool meetsRequirements = true;
+        final Map<String, dynamic> json = <String, dynamic>{
+          'hello': 'world',
+        };
+
+        final VswhereDetails result = VswhereDetails.fromJson(meetsRequirements, json);
+
+        expect(result.installationPath, null);
+        expect(result.displayName, null);
+        expect(result.fullVersion, null);
+        expect(result.isComplete, null);
+        expect(result.isLaunchable, null);
+        expect(result.isRebootRequired, null);
+        expect(result.isPrerelease, null);
+        expect(result.catalogDisplayVersion, null);
+        expect(result.isUsable, isTrue);
+      });
+
+      test('Accepts JSON', () {
+        const bool meetsRequirements = true;
+
+        final VswhereDetails result = VswhereDetails.fromJson(meetsRequirements, _defaultResponse);
+
+        expect(result.installationPath, visualStudioPath);
+        expect(result.displayName, 'Visual Studio Community 2019');
+        expect(result.fullVersion, '16.2.29306.81');
+        expect(result.isComplete, true);
+        expect(result.isLaunchable, true);
+        expect(result.isRebootRequired, false);
+        expect(result.isPrerelease, false);
+        expect(result.catalogDisplayVersion, '16.2.5');
+        expect(result.isUsable, isTrue);
+      });
+
+      test('Installation that does not satisfy requirements is not usable', () {
+        const bool meetsRequirements = false;
+
+        final VswhereDetails result = VswhereDetails.fromJson(meetsRequirements, _defaultResponse);
+
+        expect(result.isUsable, isFalse);
+      });
+
+      test('Incomplete installation is not usable', () {
+        const bool meetsRequirements = true;
+        final Map<String, dynamic> json = Map<String, dynamic>.of(_defaultResponse)
+          ..['isComplete'] = false;
+
+        final VswhereDetails result = VswhereDetails.fromJson(meetsRequirements, json);
+
+        expect(result.isUsable, isFalse);
+      });
+
+      test('Unlaunchable installation is not usable', () {
+        const bool meetsRequirements = true;
+        final Map<String, dynamic> json = Map<String, dynamic>.of(_defaultResponse)
+          ..['isLaunchable'] = false;
+
+        final VswhereDetails result = VswhereDetails.fromJson(meetsRequirements, json);
+
+        expect(result.isUsable, isFalse);
+      });
+
+      test('Installation that requires reboot is not usable', () {
+        const bool meetsRequirements = true;
+        final Map<String, dynamic> json = Map<String, dynamic>.of(_defaultResponse)
+          ..['isRebootRequired'] = true;
+
+        final VswhereDetails result = VswhereDetails.fromJson(meetsRequirements, json);
+
+        expect(result.isUsable, isFalse);
+      });
+  });
 }
 
 class VisualStudioFixture {