anchor.diff:      Cache.flutterRoot = globals.fs.path.normalize(globals.fs.path.absolute(flutterRoot));
   
       // Set up the tooling configuration.
  -    final String enginePath = _findEnginePath(topLevelResults);
  +    final String enginePath = await _findEnginePath(topLevelResults);
       if (enginePath != null) {
         contextOverrides.addAll(<Type, dynamic>{
           Artifacts: Artifacts.getLocalEngine(_findEngineBuildPath(topLevelResults, enginePath)),
  
positive.code: import 'package:completion/completion.dart';
  import 'package:file/file.dart';
  import 'package:meta/meta.dart';
  
  import '../artifacts.dart';
  import '../base/common.dart';
  
negative.code:     return null;
    }
  
    Future<String> _findEnginePath(ArgResults globalResults) async {
      String engineSourcePath = globalResults['local-engine-src-path'] as String
        ?? globals.platform.environment[kFlutterEngineEnvironmentVariableName];
  
      if (engineSourcePath == null && globalResults['local-engine'] != null) {
        try {
          final PackageConfig packageConfig = await loadPackageConfigUri(
            globals.fs.file(PackageMap.globalPackagesPath).absolute.uri,
            onError: (dynamic error) {
              // Errors indicate the automatic detection will fail, but are not
              // fatal.
            },
            loader: (Uri uri) {
              final File file = globals.fs.file(uri);
              if (!file.existsSync()) {
                return null;
              }
              return file.readAsBytes();
            },
          );
          Uri engineUri = packageConfig[kFlutterEnginePackageName]?.packageUriRoot;
          // Skip if sky_engine is the self-contained one.
          if (engineUri != null && globals.fs.identicalSync(globals.fs.path.join(Cache.flutterRoot, 'bin', 'cache', 'pkg', kFlutterEnginePackageName, 'lib'), engineUri.path)) {
            engineUri = null;
  