Deathmatch: Git Rebase vs. Merge

Deathmatch: Git Rebase vs. (Squash) Merge!

Should I Rebase? Or Squash Merge?

• Is it a personal preference?
  • Answer: Not when one or more teams are involved! Either choice will impact usability of the other!

Why does this topic evoke religious fervor?

Some engineers use knowledge of git (& the terminal) as a signal of their relative skill level. And any practice that’s tied up with our identity/ego can be impossible to analyze impartially, never mind change.

Other factors likely include Familiarity & Survivorship Bias which can further muddy our own assessment & assumptions.

Key question: What is the purpose of a git commit?

1. Do you commit early & often? Using a “checkpoint” or backup mindset?
   • Where everything is recorded, even false-starts and experiments? (e.g. git commit -am "Updated deps" && git push, repeat regularly)
   • Perhaps commit messages are less important than the code to you?
2. Or, are your commits a carefully curated, sculpted work of art?
   • Maybe each commit is a self-contained, atomic unit of work? (e.g. git add package.json && git commit -m "Updated deps")
   • Or, you simply can’t stand “messy” commit logs?
   • Do your PR reviews often involve reviewing commit-by-commit?

| 💡 What other mental model(s) define how you see commits? Please let me know @justsml!

Are you are thinking about git in a way that is providing the most value to you, your team, & your organization?

Given that there are very different mindsets around commit strategy, it’s no wonder there’s so much confusion about the “right” way to use git.

Scenario: Create a revised release tag

Let us compare the process of creating a tag release excluding some recent commits on main.

The Rebase Way

Mental model: “I want to create an alternate version of an existing history. (e.g. I made an oopsie 16 merges ago, and may need fine-grained control to correct it. Also, might get stuck in a seemingly endless cycle of conflict & --continue.)”

1. Get latest: git checkout main && git pull
2. Create new branch: git checkout -b release/hot-newness-and-stuff
3. Start interactive rebase & include the git ref for where you want to travel back in time. git rebase -i HEAD~6 (Note: HEAD~6 is ‘git ref’ shorthand for 6 commits ago)
4. Drop desired commit(s) by changing their prefix to drop. Save and close the editor.
5. Fix merge conflicts, git add . && git rebase --continue (do NOT git commit).
6. Repeat previous step until complete.
7. Tag/push using current process. Example git tag -a v1.2.3 -m 'Release v1.2.3' && git push --tags

Pros

• 🔌 Absolute power. You can change history.

Cons

• 😰 Absolute power. You can change history. (Ok, a Pro & Con…)
• 🔂 You can end up in a seemingly endless cycle of conflict & —-continue. (Sometimes even with git rerere)
• 🙀 Breaks key collaboration features: lost/orphan PR comments. Rude.
• 🖇️ Permalinks can become not that permanent.

The (Squash) Merge Way

Mental model: “I want a custom release, starting at a given point, and including any desired branch(es).”

1. Get latest: git checkout main && git pull
2. Create new branch: git checkout -b release/hot-newness-and-stuff
3. Merge in desired branches and/or commits: git merge --no-ff feature/hot-newness bug/fix-123 (use the --no-ff flag where possible.)
4. Fix any merge conflict (should it come up.)
5. Tag/push using current process. Example git tag -a v1.2.3 -m 'Release v1.2.3' && git push --tags

Pros

• 💪 Less process, fewer conflicts overall, and uses existing git command knowledge.
• 🚀 Lets you think at a higher PR/branch level, ignoring commit level granularity (unless needed.)
• 🦺 Non-destructive. You can go back and/or create new branches anytime.
• 🎥 Leaves existing commits & messages as a whole, which leads to less ‘blame’ noise.

Cons

• 🔏 Harder to change commit messages.
• 🤐 Harder to hide your work.

Conclusion

At the end of the day, a simpler process with less risk should win out.

Even though Rebasers indeed have ways to solve (or avoid) their problems, the fact remains: you’ll eventually need a black belt in git fu. (e.g. Even a humble git push can face extra complexity: was it git push --force or git push --force-with-lease? Why deal with that at all?)

There’s another reason rebasing to create a revised history will always be at a disadvantage compared to git merge .... A git merge lets the git CLI apply advanced algorithms to avoid conflicts by analyzing each branch’s HEAD.

This can be smarter because each merge only cares about the latest state of each desired branch. whereas rebasing must re-play (or drop) the commit history in the sequence specified. This limits git’s ability to optimize the merge since it only compares 2 commits at a time.

Ultimately rebasing means you’ll occasionally find yourself re-experiencing irrelevant old commits & conflicts - even if you know they have since been removed or resolved.

Summary

• 💃 Answer: SQUASH MERGE your PRs onto main.
  • Your branch history will be there if needed, and main will stay relatively “clean.”
• 🔤 Always Be Committing!
  • In >95% of corporate projects the “backup mindset” is preferable to the “sculpted art” mindset. As time goes on, your commit messages’ meaning will fade, much faster than the code whose logic & tests will maintain their significance.