implement History::truncate

[rbran]

Function used to remove multiple old history entries.

[Juhan280]

Do you think truncate is a better name for this?

[kronberger-droid]

I'd vote for it.

[rbran]

That's a way better name.

[kronberger-droid]

Do I understand this right that first of all it has no consumers and secondly could be achieved by i64::from(session)?
Seems redundant and unused.

[rbran]

that's correct, I completely missed the From<HistorySessionId> for i64

[kronberger-droid]

Don't forget to run cargo fmt with default config so CI goes green.

[kronberger-droid]

Pushed a failing test truncate_history_with_backing_file that shows FileBackedHistory::truncate doesn't persist across Drop -> sync -> reopen.
The in-memory drain works, but sync() reloads from disk and the original entries come back.

[rbran]

Having a file history with multiple sessions is significantly more complicated then I though.

If I understand correctly, will not be possible to implement nushell/nushell#18235 correctly with the current architecture.

Example of archival not triggering correctly:

• Instance 1 start (empty)
• Instance 1 create max_size - 3 history entries
• Instance 1 ends and sync
• Instance 2 start (load max_size - 3 history entries)
• Instance 3 start (load max_size - 3 history entries)
• Instance 2 create 2 history entries
• Instance 3 create 2 history entries
• Instance 2 ends and sync, just append to history file, now max_size - 1 history entries
• Instance 3 ends and sync, override the history file dropping one entry, now max_size history entries

Nushell will only be able to call count_all and get a result that is equal to max_size after entries are discarded. This will skip the archival process all together.

I will mark this PR as draft for now, fell free to close it. I'll probably create new one if I came up with an idea that don't require a big rewrite.