avoid_slow_async_io

Use of an async 'dart:io' method.

The analyzer produces this diagnostic when an asynchronous file I/O method with a synchronous equivalent is used.

The following are the specific flagged asynchronous methods:

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

The following code produces this diagnostic because the async method exists is invoked:

import 'dart:io';

Future<void> g(File f) async {
  await f.exists();
}

Use the synchronous version of the method:

import 'dart:io';

void g(File f) {
  f.existsSync();
}