anchor.diff:  
       Logger.root.level = logLevel;
   
  -    logListener = Logger.root.onRecord.listen(environment.onLog);
  +    var logListener = Logger.root.onRecord.listen(environment.onLog);
   
       /// Set up other defaults.
       debounceDelay ??= const Duration(milliseconds: 250);
  
positive.code:   // For testing only, skips the build script updates check.
    bool skipBuildScriptCheck;
  
    BuildOptions(BuildEnvironment environment,
        {@required this.packageGraph,
        BuildConfig rootPackageConfig,
        this.debounceDelay,
        this.deleteFilesByDefault,
        this.failOnSevere,
        Level logLevel,
        this.skipBuildScriptCheck,
        this.enableLowResourcesMode,
        this.outputDir,
        this.trackPerformance,
        this.verbose}) {
      // Set up logging
      verbose ??= false;
      logLevel ??= verbose ? Level.ALL : Level.INFO;
  
negative.code:           .expand((target) => target.sources.include)
            .toList();
      }
      return new BuildOptions._(
          debounceDelay: debounceDelay,
          deleteFilesByDefault: deleteFilesByDefault,
          enableLowResourcesMode: enableLowResourcesMode,
          failOnSevere: failOnSevere,
          logListener: logListener,
          outputDir: outputDir,
          packageGraph: packageGraph,
          rootPackageFilesWhitelist: rootPackageFilesWhitelist,
          skipBuildScriptCheck: skipBuildScriptCheck,
          trackPerformance: trackPerformance,
          verbose: verbose);
    }
  }
  