fs.watch doesn't emit change event when a watched folder is moved or deleted on Windows

[ARitz-Cracker]

Hello, hello! I'm back with another fs "bug"

• Version: v12.15.0
• Platform: Windows 10 1909 (x64)
• Subsystem: fs

On Linux (tested with Ubuntu 18.04 with the same NodeJS version), when you move or delete a folder watched by fs.watch, a the change event is emitted with changeType being "rename". However, on Windows, the following happens:

• Folder move within the same partition: No event is emitted
• Folder move to different partition: (untested)
• Deletion: error is emitted with "Error: EPERM: operation not permitted, watch"

Sidenote: detecting folder deletions is unreliable in general as renaming a file/folder within the watched folder with the same name as the watched folder will emit the exact same event as the watched folder itself being renamed or deleted, on Linux anyway.

[himself65]

Example

const fs = require('fs')
if (!fs.existsSync('dir'))
  fs.mkdirSync('dir')

fs.watch('./dir').on('error', console.log)

then delete folder dir

Error: EPERM: operation not permitted, watch
    at FSEvent.FSWatcher._handle.onchange (internal/fs/watchers.js:123:28) {
  errno: -4048,
  syscall: 'watch',
  code: 'EPERM',
  filename: null
}

in Ubuntu, not throw errors.

[bzoz]

We can't do anything about the folder itself being changed. You can always watch the parent folder though.

As for the EPERM - internally, we set up a callback using ReadDirectoryChangesW. When the folder is deleted, the callback returns ERROR_ACCESS_DENIED which gets translated into EPERM. So again - nothing we can really do about it.

I'll open a PR to add those two things to the "caveats" section of the fs.watch documentation.