Ignore replacement characters from vswhere.exe output (#104284)

Flutter uses `vswhere.exe` to find Visual Studio installations and determine if they satisfy Flutter's requirements. However, `vswhere.exe`'s JSON output is known to contain bad UTF-8. This change ignores bad UTF-8 as long as they affect JSON properties that are either unused, or, used only for display purposes by Flutter.

Fixes: flutter/flutter#102451

Author: loic-sharma

packages/flutter_tools/lib/src/convert.dart

@@ -26,10 +26,14 @@ const Encoding utf8ForTesting = cnv.utf8;
 /// that aren't UTF-8 and we're not quite sure how this is happening.
 /// This tells people to report a bug when they see this.
 class Utf8Codec extends Encoding {
-  const Utf8Codec();
+  const Utf8Codec({this.reportErrors = true});
+
+  final bool reportErrors;
 
   @override
-  Converter<List<int>, String> get decoder => const Utf8Decoder();
+  Converter<List<int>, String> get decoder => reportErrors
+    ? const Utf8Decoder()
+    : const Utf8Decoder(reportErrors: false);
 
   @override
   Converter<String, List<int>> get encoder => cnv.utf8.encoder;

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

@@ -47,12 +47,14 @@ class VisualStudio {
 
   /// The name of the Visual Studio install.
   ///
-  /// For instance: "Visual Studio Community 2019".
+  /// For instance: "Visual Studio Community 2019". This should only be used for
+  /// display purposes.
   String? get displayName => _bestVisualStudioDetails?.displayName;
 
   /// The user-friendly version number of the Visual Studio install.
   ///
-  /// For instance: "15.4.0".
+  /// For instance: "15.4.0". This should only be used for display purposes.
+  /// Logic based off the installation's version should use the `fullVersion`.
   String? get displayVersion => _bestVisualStudioDetails?.catalogDisplayVersion;
 
   /// The directory where Visual Studio is installed.
@@ -282,12 +284,15 @@ class VisualStudio {
         '-utf8',
         '-latest',
       ];
+      // Ignore replacement characters as vswhere.exe is known to output them.
+      // See: https://github.com/flutter/flutter/issues/102451
+      const Encoding encoding = Utf8Codec(reportErrors: false);
       final RunResult whereResult = _processUtils.runSync(<String>[
         _vswherePath,
         ...defaultArguments,
         ...?additionalArguments,
         ...requirementArguments,
-      ], encoding: utf8);
+      ], encoding: encoding);
       if (whereResult.exitCode == 0) {
         final List<Map<String, dynamic>> installations =
             (json.decode(whereResult.stdout) as List<dynamic>).cast<Map<String, dynamic>>();
@@ -416,17 +421,40 @@ class VswhereDetails {
 
     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?,
+
+      // Below are strings that must be well-formed without replacement characters.
+      installationPath: _validateString(details['installationPath'] as String?),
+      fullVersion: _validateString(details['installationVersion'] as String?),
+
+      // Below are strings that are used only for display purposes and are allowed to
+      // contain replacement characters.
+      displayName: details['displayName'] as String?,
       catalogDisplayVersion: catalog == null ? null : catalog['productDisplayVersion'] as String?,
     );
   }
 
+  /// Verify JSON strings from vswhere.exe output are valid.
+  ///
+  /// The output of vswhere.exe is known to output replacement characters.
+  /// Use this to ensure values that must be well-formed are valid. Strings that
+  /// are only used for display purposes should skip this check.
+  /// See: https://github.com/flutter/flutter/issues/102451
+  static String? _validateString(String? value) {
+    if (value != null && value.contains('\u{FFFD}')) {
+      throwToolExit(
+        'Bad UTF-8 encoding (U+FFFD; REPLACEMENT CHARACTER) found in string: $value. '
+        'The Flutter team would greatly appreciate if you could file a bug explaining '
+        'exactly what you were doing when this happened:\n'
+        'https://github.com/flutter/flutter/issues/new/choose\n');
+    }
+
+    return value;
+  }
+
   /// Whether the installation satisfies the required workloads and minimum version.
   final bool meetsRequirements;
 

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

@@ -864,6 +864,85 @@ void main() {
     });
   });
 
+  // The output of vswhere.exe is known to contain bad UTF8.
+  // See: https://github.com/flutter/flutter/issues/102451
+  group('Correctly handles bad UTF-8 from vswhere.exe output', () {
+    late VisualStudioFixture fixture;
+    late VisualStudio visualStudio;
+
+    setUp(() {
+      fixture = setUpVisualStudio();
+      visualStudio = fixture.visualStudio;
+    });
+
+    testWithoutContext('Ignores unicode replacement char in unused properties', () {
+      final Map<String, dynamic> response = Map<String, dynamic>.of(_defaultResponse)
+        ..['unused'] = 'Bad UTF8 \u{FFFD}';
+
+      setMockCompatibleVisualStudioInstallation(
+        response,
+        fixture.fileSystem,
+        fixture.processManager,
+      );
+
+      expect(visualStudio.isInstalled, true);
+      expect(visualStudio.isAtLeastMinimumVersion, true);
+      expect(visualStudio.hasNecessaryComponents, true);
+      expect(visualStudio.cmakePath, equals(cmakePath));
+      expect(visualStudio.cmakeGenerator, equals('Visual Studio 16 2019'));
+    });
+
+    testWithoutContext('Throws ToolExit on bad UTF-8 in installationPath', () {
+      final Map<String, dynamic> response = Map<String, dynamic>.of(_defaultResponse)
+        ..['installationPath'] = '\u{FFFD}';
+
+      setMockCompatibleVisualStudioInstallation(response, fixture.fileSystem, fixture.processManager);
+
+      expect(() => visualStudio.isInstalled,
+          throwsToolExit(message: 'Bad UTF-8 encoding (U+FFFD; REPLACEMENT CHARACTER) found in string'));
+    });
+
+    testWithoutContext('Throws ToolExit on bad UTF-8 in installationVersion', () {
+      final Map<String, dynamic> response = Map<String, dynamic>.of(_defaultResponse)
+        ..['installationVersion'] = '\u{FFFD}';
+
+      setMockCompatibleVisualStudioInstallation(response, fixture.fileSystem, fixture.processManager);
+
+      expect(() => visualStudio.isInstalled,
+          throwsToolExit(message: 'Bad UTF-8 encoding (U+FFFD; REPLACEMENT CHARACTER) found in string'));
+    });
+
+    testWithoutContext('Ignores bad UTF-8 in displayName', () {
+      final Map<String, dynamic> response = Map<String, dynamic>.of(_defaultResponse)
+        ..['displayName'] = '\u{FFFD}';
+
+      setMockCompatibleVisualStudioInstallation(response, fixture.fileSystem, fixture.processManager);
+
+      expect(visualStudio.isInstalled, true);
+      expect(visualStudio.isAtLeastMinimumVersion, true);
+      expect(visualStudio.hasNecessaryComponents, true);
+      expect(visualStudio.cmakePath, equals(cmakePath));
+      expect(visualStudio.cmakeGenerator, equals('Visual Studio 16 2019'));
+      expect(visualStudio.displayName, equals('\u{FFFD}'));
+    });
+
+    testWithoutContext("Ignores bad UTF-8 in catalog's productDisplayVersion", () {
+      final Map<String, dynamic> catalog = Map<String, dynamic>.of(_defaultResponse['catalog'] as Map<String, dynamic>)
+        ..['productDisplayVersion'] = '\u{FFFD}';
+      final Map<String, dynamic> response = Map<String, dynamic>.of(_defaultResponse)
+        ..['catalog'] = catalog;
+
+      setMockCompatibleVisualStudioInstallation(response, fixture.fileSystem, fixture.processManager);
+
+      expect(visualStudio.isInstalled, true);
+      expect(visualStudio.isAtLeastMinimumVersion, true);
+      expect(visualStudio.hasNecessaryComponents, true);
+      expect(visualStudio.cmakePath, equals(cmakePath));
+      expect(visualStudio.cmakeGenerator, equals('Visual Studio 16 2019'));
+      expect(visualStudio.displayVersion, equals('\u{FFFD}'));
+    });
+  });
+
   group(VswhereDetails, () {
       test('Accepts empty JSON', () {
         const bool meetsRequirements = true;