Abstract:

In this talk, Andre Arco presents "Stupid JJ Tricks," a comprehensive tour of advanced and creative configurations for the JJ version control system. Sourced from online communities and personal experimentation, the presentation moves from foundational setups to complex automations. It covers essential configurations like customizing diff/merge tools and user identity, then dives deep into JJ's powerful templating system for creating verbose commit messages, custom log outputs, and even machine-readable JSON. The talk also explores the utility of revset aliases for defining logical groups of commits (e.g., "mine," "work-in-progress," "stack"). Key, yet often overlooked, commands like jj absorb, jj parallelize, and jj fix are highlighted for their ability to streamline complex refactoring workflows. Finally, the presentation showcases sophisticated aliases that automate interaction with Git remotes and introduces several "cursed" but highly effective tricks, such as a fuzzy bookmark finder and a method for counting commits using templates and shell pipelines.

A Tour of Powerful and Creative JJ Configurations

• 0:01:02 - Foundational Configuration: The talk begins with essential global configurations, including setting your name and email based on repository path, and customizing the tools used for diffing (diffastic, delta) and merging (meld, merger).
• 0:03:16 - Customizing Default Commands: You can change JJ's default behavior, such as setting the default command (what runs when you type jj) to jj status instead of jj log, or altering the default set of commits (revset) shown by the log.
• 0:05:16 - Verbose Commit Messages via Templates: A template can be configured to automatically include the diff of your changes within your commit message editor, mimicking the behavior of git commit --verbose.
• 0:06:39 - Overriding Template Fragments: Instead of rewriting entire templates, you can customize small, reusable parts ("fragments"). Examples include changing all timestamps to UTC or a relative format (e.g., "7 months ago") or modifying log graph icons to indicate which commits are ready to be pushed.
• 0:09:34 - Generating Machine-Readable Output: JJ's templating engine includes an escape_json function, making it possible to create valid JSON output directly from commands. This is useful for scripting and integration with other tools like jq.
• 0:10:53 - Creating Powerful Revset Aliases: Revsets are used to define and name custom sets of commits. Common aliases include mine (commits authored by you), WIP (work-in-progress commits to be excluded from pushes), and the concept of a stack to manage a group of related commits.
• 0:15:32 - Highlighting Powerful Built-in Commands:
  • jj absorb: A powerful command that automatically finds the correct parent commits for your current changes and squashes them in, saving you from manual split and squash operations.
  • jj parallelize: Automatically restructures a linear chain of dependent commits into parallel, independent branches off a common ancestor.
  • jj fix: Runs a specified command, like a linter or formatter, on every commit in a revision set, which is excellent for cleaning up history before pushing.
• 0:18:30 - Advanced Workflow Automation with Aliases: The talk demonstrates several complex aliases for a seamless Git-integrated workflow:
  • tug: A popular alias for moving a bookmark to the latest "pushable" commit in a stack.
  • ghpr: An alias that automates creating a GitHub pull request by finding the correct bookmark and passing it to the gh CLI tool.
  • pull and push: A suite of heavily automated aliases that manage fetching from a Git remote, rebasing local changes, tugging bookmarks, pushing, and setting up tracking branches.
• 0:24:31 - "Stupid" But Effective Tricks: The presentation concludes with creative, non-obvious solutions to common problems:
  • Counting Commits: A workaround to count commits is to use a template that prints a single character per commit and then pipe the output to wc -c.
  • Enhanced Log: An alias (jll) is shown that combines the output of jj log with jj status for the three most recent commits, giving a more detailed view of recent work.
  • Fuzzy Finder for Bookmarks: An alias (jjz) that uses a fuzzy finder like fzf to quickly search for and switch to any bookmark by typing a few characters of its name.