anchor.diff:  final RegExp _importPattern = RegExp(r'''^\s*import (['"])package:flutter/([^.]+)\.dart\1''');
   final RegExp _importMetaPattern = RegExp(r'''^\s*import (['"])package:meta/meta\.dart\1''');
   
  -Set<String> _findFlutterDependencies(String srcPath, List<String> errors, { bool checkForMeta = false }) {
  -  return _allFiles(srcPath, 'dart', minimumMatches: 1)
  +Future<Set<String>> _findFlutterDependencies(String srcPath, List<String> errors, { bool checkForMeta = false }) async {
  +  return await _allFiles(srcPath, 'dart', minimumMatches: 1)
       .map<Set<String>>((File file) {
         final Set<String> result = <String>{};
         for (final String line in file.readAsLinesSync()) {
  
positive.code:   return true;
  }
  
  Iterable<File> _allFiles(String workingDirectory, String extension, { @required int minimumMatches }) sync* {
    assert(extension == null || !extension.startsWith('.'), 'Extension argument should not start with a period.');
    final Set<FileSystemEntity> pending = <FileSystemEntity>{ Directory(workingDirectory) };
    int matches = 0;
  
negative.code: 
  Future<void> verifyDeprecations(String workingDirectory, { int minimumMatches = 2000 }) async {
    final List<String> errors = <String>[];
    await for (final File file in _allFiles(workingDirectory, 'dart', minimumMatches: minimumMatches)) {
      int lineNumber = 0;
      final List<String> lines = file.readAsLinesSync();
      final List<int> linesWithDeprecations = <int>[];
  