Only first change event detected when multiple watchers add same file

[zqianem]

Describe the bug

If there are multiple instances of a Chokidar watcher watching the same file, only the first change to a file is detected.

Versions:

• Chokidar version [3.5.3]
• Node version [v16.16.0]
• OS version: [Arch Linux x86_64 Kernel 5.18.16-arch1-1]

To Reproduce:

Edit: could not reproduce on Windows 11

On a non-memory filesystem (i.e. not /tmp), run node main.mjs and create/edit hello.txt in the same directory.

// main.mjs
import chokidar from 'chokidar'

let w1 = chokidar
  .watch([])
  .on('all', (event, path) => console.log('w1', { event, path }))

let w2 = chokidar
  .watch([])
  .on('all', (event, path) => console.log('w2', { event, path }))

// if either of the following lines are commented out, change events continue to fire as expected
w1.add('hello.txt')
w2.add('hello.txt')

This outputs:

w1 { event: 'add', path: 'hello.txt' }
w2 { event: 'add', path: 'hello.txt' }
w1 { event: 'change', path: 'hello.txt' }
w2 { event: 'change', path: 'hello.txt' }
# further edits to hello.txt do not cause additional change events

Oddly, there was one time in my testing where the change events did continue to fire with the above setup after I added node main.mjs to package.json's scripts field, but I could not reproduce it again.

Expected behavior

When hello.txt is edited multiple times, change events continue to fire:

w1 { event: 'add', path: 'hello.txt' }
w2 { event: 'add', path: 'hello.txt' }
w1 { event: 'change', path: 'hello.txt' }
w2 { event: 'change', path: 'hello.txt' }
w1 { event: 'change', path: 'hello.txt' }
w2 { event: 'change', path: 'hello.txt' }
w1 { event: 'change', path: 'hello.txt' }
w2 { event: 'change', path: 'hello.txt' }
# etc

Additional context

Likely the cause of rollup/rollup#4508, as Rollup ends up having multiple watchers for files added by plugins via addWatchFile.

[gajus]

@paulmillr Any pointers of what could be happening here?

Happy to help debug and submit PR if releasing this can get prioritized.

[zqianem]

Tested this and seems to be fixed as of v4.01 🎉