avoid_slow_async_io

Avoid slow async dart:io methods.

This rule is available as of Dart 2.0.0.

AVOID using the following asynchronous file I/O methods because they are much slower than their synchronous counterparts.

• Directory.exists
• Directory.stat
• File.lastModified
• File.exists
• File.stat
• FileSystemEntity.isDirectory
• FileSystemEntity.isFile
• FileSystemEntity.isLink
• FileSystemEntity.type

BAD:

import 'dart:io';

Future<Null> someFunction() async {
  var file = File('/path/to/my/file');
  var now = DateTime.now();
  if ((await file.lastModified()).isBefore(now)) print('before'); // LINT
}

GOOD:

import 'dart:io';

Future<Null> someFunction() async {
  var file = File('/path/to/my/file');
  var now = DateTime.now();
  if (file.lastModifiedSync().isBefore(now)) print('before'); // OK
}

To enable the avoid_slow_async_io rule, add avoid_slow_async_io under linter > rules in your analysis_options.yaml file:

linter:
  rules:
    - avoid_slow_async_io