Fixing Problems

At some point, we’re going to make a mistake. We may abandon the wrong change, squash something into the wrong parent, or resolve a conflict and then realize we preferred the other version.

If you’ve used git for a while, you may have reached for git reflog, found a hash that looked about right, and tried to put things back together. This often works, but it can feel a bit like emergency recovery.

Recovery works differently in jj. Every command we run is recorded, the old state is kept, and going back is a normal part of the tool rather than a separate emergency procedure.

Here’s what we’re going to learn:

• Undoing your last command with jj undo
• Reading the history of your repository’s states with jj op log, and jumping back to one
• Watching a single change evolve over time with jj evolog
• Recognizing and untangling divergent changes, where two visible commits claim the same change ID
• Throwing away changes on purpose, with jj restore and jj revert
• Hunting down the change that broke something, with jj bisect

You’ve already used jj undo a couple of times in this book, on the promise that I’d explain it later. It’s later.