File is not tracked when is/was ignored and watchman is enabled

[fgsch]

Description

I had a file in .gitignore. jj file track --include-ignored didn't track the file.
I then removed the pattern from .gitignore. Running git status shows the file as untracked, but jj still doesn't track it automatically or manually after running jj file track.

@bryceberger asked whether I was using watchman and commented they had issues with it not picking up new files if they were originally on the ignore list.

I disabled watchman and the file started showing.

Steps to Reproduce the Problem

1. Enable watchman
2. Add file to .gitignore
3. Run jj file track --include-ignored file
4. Remove file from .gitignore
5. Run jj status or jj file track file

Expected Behavior

1. File is tracked automatically when removed from .gitignore
2. File is tracked even if it's in .gitignore after running jj file track --include-ignored file

Actual Behavior

File is not tracked

Specifications

• Platform: macos 26.1
• Version: jj 0.36.0
• Watchman: 2025.12.22.00

[fgsch]

Maybe duplicated of #8298 ?

[yuja]

The problem is similar to #2613, but I think we should disable watchman when doing explicit tracking. The last watchman state cannot be trusted if tracking scope is changed.

[bryceberger]

That's similar to what I thought, but if watchman cannot be trusted to give the event when tracking, can it be trusted to give any further events?

1. Watchman ignores the file, since it's in the gitignore
2. User explicitly jj file track --include-ignored, so jj manually looks at the path
3. In the future, jj asks watchman what files are changed. Watchman still thinks the file is ignored
4. Potentially weird snapshots where only some files are updated?

I'm not an expert on how watchman tracks files, so maybe this is a non-issue, or maybe there's a way to provide watchman an explicit list of what to track?

[yuja]

Perhaps, we'll need to distrust the previous watchman_clock and do full scan when tracking scope (or .gitignore) changed. After the full scan, the watchman state (or changed files since the last full scan) should be good.

[arxanas]

I don't recall what the current integration is between Watchman and .gitignores. If we convert .gitignore patterns into watch patterns, then we also need to add a general watch pattern for all .gitignores (even those which themselves are .gitignored!) and do a full re-scan. (There are probably other sound schemes, but that would be easiest.)