How did `git pull` eat my homework?

Yes, git ate my homework. All of it.

I made a dd image of this disk after the incident and messed around with it later. Reconstructing the series of events from system logs, I deduce what happened was something like this:

1. A system update command (pacman -Syu) had been issued days before this incident.
2. An extended network outage meant that it was left re-trying to download packages. Frustrated at the lack of internet, I'd put the system to sleep and gone to bed.
3. Days later the system was woken up and it started finding and downloading packages again.
4. Package download finished sometime just before I happened to be messing around with this repository.
5. The system glibc installation got updated after the git checkout and before the git pull.
6. The git binary got replaced after the git pull started and before it finished.
7. And on the seventh day, git rested from all its labors. And deleted the world so everybody else had to rest too.

I don't know exactly what race condition occurred that made this happen, but swapping out binaries in the middle of an operation is certainly not nice nor a testable / repeatable condition. Usually a copy of a running binary is stored in memory, but git is weird and something about the way it re-spawns versions of itself I'm sure led to this mess. Obviously it should have died rather than destroying everything, but that's what happened.

Possibly by failing at defining the file path to be deleted.

Your case reminded me a beautiful day that when my homemade remove(path) method tried to remove the root folder because the given parameter was empty string which the OS corrected (!) as the root folder.

This may be a similar git bug. Such that:

1. Rebase command wanted to delete a file like remove(project_folder + file_path) (pseudo code)
2. Somehow file_path was empty at the time.
3. Command evaluated as some thing like remove(project_folder)