`jj file track` + `jj undo` deletes the file

[jakobhellermann]

Description

I'm not sure if this is a bug report or a feature request for a warning. But especially if you have snapshot.auto-track = none() you might want to track a folder, notice that you didn't want to track the entire folder, do jj undo, and then your files are gone.

Steps to Reproduce the Problem

1. jj config set --repo 'snapshot.auto-track' 'none()'
2. touch foo
3. jj file track foo
4. jj undo

Expected Behavior

Multiple options:

• just untrack the file again, keeping it on disk
• warn that the file was removed, suggesting jj file untrack for non-destructive revert

Actual Behavior

The file that was tracked is deleted. Restoring it is not too hard if you know your way around the op log and notice it immediately.

Specifications

• Platform: Linux
• Version: 0.40.0

[joyously]

This points exactly to what I was saying long ago: there should be one source of truth for ignoring or tracking files, and anything ignored(not tracked) should not be touched(or deleted).

[yuja]

Since old untracked files aren't managed by jj, this is expected. Maybe we can add a warning to jj undo.