FR: Recover command for corrupt repo and/or troubleshooting documentation

[dhardy]

Is your feature request related to a problem? Please describe. Yes; the repository can become corrupt as in #4423.

Describe the solution you'd like While investigating a corrupt repo (no valid operation in .jj/repo/op_heads/heads/), I was able to find the last valid prior operation in .jj/repo/op_store/operations/. There should be some command (or at least a how-to) for restoring to such an operation.

jj op restore HASH fails since the first thing fn cmd_op_restore tries to do is construct a workspace:

    // NOTE: this fails since the op log does not have a valid head
    let mut workspace_command = command.workspace_helper(ui)?;

It is trivial to resolve the target_op without a workspace_command:

    let target_op = jj_lib::op_walk::resolve_op_for_load(workspace.repo_loader(), &args.operation)?;

However, it is very much not trivial to apply a transaction — I'm not even sure it makes sense to try given that a transaction must have a valid initial state!

Describe alternatives you've considered Ideally, it would be impossible for a repo to become corrupted. But even if all filesystem commits were atomic and all bugs squashed, there would still be other possible causes (especially user error).

There might be a dedicated recovery command for common (resolvable) issues?

There could simply be good documentation on the filesystem format with tips on troubleshooting.

[PhilipMetzger]

Describe alternatives you've considered Ideally, it would be impossible for a repo to become corrupted. But even if all filesystem commits were atomic and all bugs squashed, there would still be other possible causes (especially user error).

There might be a dedicated recovery command for common (resolvable) issues?

We previously talked about a jj doctor/jj util recover command in the Discord but nothing has happened in its direction.

[dhardy]

I updated my "guide" on recovering the repo in the other thread. Unfortunately it leaves another unsolved problem: commits which appear in jj's log but which do not exist when I attempt to edit / new / diff -r / abandon them.