Chokidar will trigger for unmodified files on Windows when LastAccessTime is changed

[mikemaccana]

Given the following in Windows:

var watcher = chokidar.watch(dir, {
    ignored: ignored,
    persistent: true,
    usePolling: config.options.legacyWatch || false,
    interval: config.options.pollingInterval,
});

When a file is opened but not modified, Chokidar will trigger a change as LastAccessTime is modified. All other attributes remain unchanged. See remy/nodemon#1208

Versions (please complete the following information):

• Chokidar version: 170
• Node version: v8.11.2
• OS version: Microsoft Windows NT 10.0.17713.0

To Reproduce
Just open a file (changing LastAccessTime on a watched file. LMK if you want a demo app.

Expected behavior
No changes. Access Time is not considered a change. It is reading, not writing.

[dariocravero]

I can confirm that this is happening on Mac too.

I wrote this script to try to work out what's going on:

const childProcess = require('child_process')
const chokidar = require('chokidar')
const fs = require('fs-extra')

async function run() {
  await fs.unlink('file')
  await fs.writeFile('file', 'content')

  setTimeout(() => {
    const watcher = chokidar.watch('file', {
      // we need the stat
      alwaysStat: true,

      // doesn't do it
      // ignore(path, stat) {
      //   return (stat.atimeMs > stat.mtimeMs)
      // },
      ignoreInitial: true,
    })

    let changes = 0
    watcher.on('change', (file, stat = {}) => {
      // this does it
      if (stat.atimeMs > stat.mtimeMs) return

      changes++
    })

    watcher.on('ready', async () => {
      setTimeout(() => childProcess.spawnSync('open', ['file']), 250)

      setTimeout(() => fs.writeFile('file', 'more content'), 1500)

      setTimeout(() => {
        watcher.close()

        console.log('registered one change', changes === 1)
      }, 3000)
    })
  }, 1000)
}

run()

We can bail on change if the access time is newer than the modified time. I tried doing it on the ignore option but it doesn't do what I thought it did :).

Is this something that chokidar should handle internally?

[goser]

Adding

if (event === 'change' && val1.atime && val1.mtime && val1.atime > val1.mtime) {
    return this;
}

to FSWatcher.prototype._emit worked for me as a hotfix but I am not sure if it would break other projects.

[mikemaccana]

@goser Send it as a PR and mark it as 'fixes #750'. It'll get more attention and someone will review it.

[markablov]

#762

[straussdd]

I'm running nodemon in a Visual Studio Code task and this behavior is really annoying. VS Code will sporadically cause the access time of multiple files to be updated whenever its git autorefresh feature runs in the background. So I really appreciate your PR, @markablov

[johannreboulleau]

Hello,
We had the same problem, and we fix it thanks to the solution of @svogal

[7iomka]

Hello,
We had the same problem, and we fix it thanks to the solution of @svogal

Thank you!

[mikemaccana]

Looks like this is in 2.1.0, see https://www.npmjs.com/package/chokidar/v/2.1.0