Rebase Workflow Workshop

Warm Up in Breakout Rooms

• Using a merge workflow, how are commits organized in the timeline?
• How is a rebase workflow different in how commits are organized?
• What are the benefits and downsides of using one versus the other? Is one better than the other?

Exercise 1 (Initial commits and setting up a PR)

The rebase workflow has a lot of similarities to the merge workflow, especially around resolving conflicts that arise when multiple contributors are working on the same codebase. While there are a few different ways of doing this, we’ll cover one way you can approach it.

1. Checkout a new branch (branch1) off of main and make some edits by adding or removing lines from the README or creating new files with some content.
2. Create 3 new commits on this branch (branch1). Run git log and note the three new commits that you have added. (you can exit the log by hitting q)
3. Checkout another branch (branch2) off of main and make some edits here as well. You only need to create 1 new commit on this branch.
4. Next, go back to your previous branch (branch1), and push up your branch to GitHub with git push origin <branch_name>. Then go to your GH repo and click Compare & pull request.
5. When you open the pull request, change the base repository to be your repository. (NOT “Kalikoze”!). Then click Create pull request.

Exercise 2 (Interactive Rebase)

Let’s say we’re looking at those three commits, and they all appear to be tied together and likely could be one larger commit. Now is a perfect time for interactive rebase! Interactive rebase allows us to manipulate our commit history by editing our commits. Here are some tips to working through the interactive rebase flow!

1. In your terminal, run git log --oneline in branch1 to see the 3 commits you just created.
   • Looking at them, you’ll notice you’ve made multiple changes all relating to the README. Wouldn’t it be nice to combine (ie. squash) them into one?
2. To squash all three of them, run git rebase -i <hash> (ie 98b1875) or run git rebase -i HEAD~3.
   • Take a look at the note underneath Exercise #2 for questions about which hash to pick or what HEAD~3 mean!
   • Note: When in the interactive rebase, it is possible that you’ll be in VIM mode (where you are editing code in the terminal). In order to edit anything first type i for insert. Once you are done editing, press esc. Then type :wq (this will save your changes). If it opens up VSCode or Atom, edit the scripts and save as your normally would before closing out of it.

pick c3a27af Remove requirements from README
pick 255ed0e Update first installation instruction
pick 2fb87ae Update troubleshooting section of README

# Rebase 98b1875..2fb87ae onto 98b1875 (3 commands)
#
# Commands:
# p, pick <commit> = use commit
# r, reword <commit> = use commit, but edit the commit message
# e, edit <commit> = use commit, but stop for amending
# s, squash <commit> = use commit, but meld into previous commit
# f, fixup <commit> = like "squash", but discard this commit's log message
# x, exec <command> = run command (the rest of the line) using shell
# b, break = stop here (continue rebase later with 'git rebase --continue')
# d, drop <commit> = remove commit
# l, label <label> = label current HEAD with a name
# t, reset <label> = reset HEAD to a label
# m, merge [-C <commit> | -c <commit>] <label> [# <oneline>]
# .       create a merge commit using the original merge commit's
# .       message (or the oneline, if no original merge commit was
# .       specified). Use -c <commit> to reword the commit message.
#
# These lines can be re-ordered; they are executed from top to bottom.
#
# If you remove a line here THAT COMMIT WILL BE LOST.
#
# However, if you remove everything, the rebase will be aborted.

1. Replace the word pick with squash in front of two of the commit hashes (It shouldn’t matter which ones since you will effectively be combing all three into one. However, if it doesn’t work correctly, experiment with different ones).
2. Then save your changes. (In VIM mode, press esc and type :wq)
3. You’ll see a new message with the three commits messages you previously made.
   • This is your opportunity to edit/write (remember to press i in VIM mode) the commit messages you want to use. If you did not edit any of the messages it would keep them all.
   • Remove two of the commit messages and change the final one to be the new message describing the changes made.
4. After editing, save your changes once more.

In the terminal you should now see: Successfully rebased and updated refs/heads/<branch_name>.

Now when you run git log --oneline there should no longer be 3 new commits, but instead one commit with the new message you wrote. Cheers!

Exercise 3 (Pushing your new timeline up to GitHub)

Now that we’ve done that, take a look at your PR. Note that there are still three commits there. It’s not up to date with our local repo.

1. Try pushing up your branch again and take note of what it says.
   • Because we are rewriting the commit timeline, it’s not allowing us to push up to our remote respository (it acts as a safety measure)
2. To fix this and rewrite the timeline, you can run git push -f origin <branch_name>.
   • The -f means to forcefully push up and rewrite the timeline which is necessary for this rebase because we want to combine these commits
3. Then check your Pull Request and check if it now only displays one commit.
4. After confirming that there is only one commit (you may need to refresh GitHub), then click on Merge pull request to merge the branch into main.

Exercise 4 (Bringing those changes to Branch 2)

Remember that we had created two branches? What if we wanted to pull in our latest changes from main into our second branch?

1. Checkout main and pull down your latest changes from GitHub.
2. Then checkout branch2 and run git rebase main to bring in the latest changes.
   • Note because there were changes made in a similar file, you may need to deal with merge conflicts.
3. Work through the merge conflicts, add them, and then run git rebase --continue to finish up. You can then run git log to see your new and improved timeline!