Initially-gitignored file continually reappears (with watchman)

[glencbz]

Description

In some cases, a .gitignored file in one commit can get tracked by another commit, but the file seems to stick around in the working copy outside of the commits, ready to be tracked again!

The commit topology is like:

@
|
A  B
| /
P

where in A, there is a .gitignore that ignores /path/to/ignored. /path/to/ignored is in the working copy. B doesn't have the .gitignore

now, checking out B:

   @
   |
A  B
| /
P

puts /path/to/ignored in @.

Other, possibly relevant information:

• /path/to/ignored is owned by root (it was generated by something in a Docker container).
• /path/to/ignored is binary.

Expected/Actual Behavior

• jj abandon should delete the file and recreate an empty working copy commit. Instead, the newly created working copy commit still has /path/to/ignored.
• jj co B should create an empty working copy commit. Instead, every working copy commit has /path/to/ignored in it (also causing the working copy commits to not be auto-abandoned).
• jj co <yet another unrelated commit> after jj co B also gives similar results to jj co B

Fixable by deleting /path/to/ignored, as one might expect.

Specifications

• Platform: Ubuntu 22.04.2 on WSL, installed via https://github.com/martinvonz/jj/releases/download/v0.10.0/jj-v0.10.0-x86_64-unknown-linux-musl.tar.gz. A colleague of mine also experienced this on MacOS (I believe).
• Version: v0.10.0

[yuja]

Do you enable watchman? The un-ignored file is unmodified in the working copy, so it wouldn't be detected by watchman.

Perhaps, watchman clock would need to be reset on ignore pattern changed, (or contain hash of active ignore patterns) to detect changes.

[glencbz]

Dumb question: how can I tell if I've enabled watchman? 😅

[yuja]

Try jj config list core.fsmonitor. It's disabled by default. jj status -v will also print something like "Querying Watchman".

I can reproduce the problem with fsmonitor = "watchman".

[ilyagr]

Minor updates to Yuya's last comment: these days, you can use jj debug watchman status and other jj debug watchman commands. Today, it would also be jj status --debug instead of jj status -v.