fs.watch() reports removed directory as subdirectory of itself #25301

• Affected versions: Latest release of Current and all LTSes - 11.6.0, 10.15.0, 8.15.0, and 6.16.0.
• Affected platform: Linux (ok on macOS/Windows)
• Subsystem: fs

Description

When using fs.watch() to watch a directory, and removing that very directory itself, a change event is emitted with a filename matching the directory itself.

To my knowledge, the standard way to obtain an absolute path of the affected file, is to path.join() the filename with the directory being watched.

As such, the emitted event is interpreted as if a subdirectory changed, which is incorrect.

Test case

Code at https://github.com/Krinkle/sandbox/blob/node-fs-watch-removedir/test.js.

Build output:

• Linux / Node 11.6.0: https://travis-ci.com/Krinkle/sandbox/jobs/167657972
• Linux / Node 10.15.0: https://travis-ci.com/Krinkle/sandbox/jobs/167657973
• .. for Node 8, 6 and macOS/Windows, see https://travis-ci.com/Krinkle/sandbox/builds/96013157.

In brief:

1. Given a directory structure as follows:

    - home/
          - a/
             - file1
          - b/
             - file1
             - file2
          - c/

2. And creating an fs.FSWatcher for home/ and home/c, via fs.watch(dir, { encoding: 'utf8', recursive: false }).
3. And removing home/c/ via fs.rmdirSync(dir).

Expected

Change event for home/ or home/c/. Specifically, one or more of:

• An event on home/ with a filename of 'c', '/c', or no filename.
• An event on home/c/ with a filename of '' (empty string),'.' (empty string), '/', or no filename.

Actual

On macOS, gets a change event for home/c/ as expected:

1. FSWatcher for home/ receives change event; eventType=rename, filename=c

On macOS, gets a change event for home/c/ as expected:

1. FSWatcher for home/ receives change event; eventType=rename, filename=c

On Linux, gets change events for /home/c/c/: ❌

1. FSWatcher for home/c/ receives change event; eventType=rename, filename=c ❌
2. FSWatcher for home/c/ receives change event; eventType=rename, filename=c ❌
3. FSWatcher for home/ receives change event; eventType=rename, filename=c ✅