alef83 / git-rebase-workshop

git-rebase-workshop

Background

During the development process the code changes relate to each feature are being committed to separate feature branch. Due to the fact that the team works on several features in parallel in most cases the default branch's head commit changes since a feature branch created until it is merged. So, the developer that wants to merge their changes into the default branch first should update the feature branch. There are two main options to do it: merge and rebase.

Initial state

After Merge

After Rebase

Merging feature branches to the default branch

Rebasing feature branch on Github

Rebase Props and Cons

• Prop: The PR is tidier and contains only relevant to the work on the feature commits.
• Cons: The conflicts resolution process is more challenging.

Note: Using merge we need to solve conflicts only once. For rebase we have to do it almost for each commit. If we'd have multiple commits in the branch the rebase could be very hard and painful process. The solution is to keep the branch lean.

Workshop

Simple case

1. Create folder for workshop and initialize git

   mkdir workshop
   cd workshop
   git init
   git commit --allow-empty -m "First commit"
   git commit --allow-empty -m "Second commit"
   git commit --allow-empty -m "Third commit"
   git --no-pager log --format=oneline

2. Create the big feature branch with one commit

   git checkout -b my-big-feature
   touch big-feature-file.txt
   echo Hello > big-feature-file.txt
   git add big-feature-file.txt
   git commit -m "feat: the first big feature commit"

3. Return to the main branch

   git checkout -

4. Create the small feature branch with two commits

   git checkout -b my-small-feature
   touch small-feature-file.txt
   echo "Hello" > small-feature-file.txt
   git add small-feature-file.txt
   git commit -m "feat: the small feature first commit"
   echo "World" >> small-feature-file.txt
   git add small-feature-file.txt
   git commit -m "feat: the small feature second commit"
   git --no-pager log --format=oneline

5. Merge it into main branch

   git checkout main
   git merge --squash my-small-feature
   git commit -m "feat: the small feature"
   git branch -D my-small-feature
   git --no-pager log --format=oneline

6. Find last commit that is common for the feature and the default branch

   git checkout my-big-feature
   echo "Last common commit: " `git merge-base my-big-feature main`
   git --no-pager log --format=oneline

7. Rebase the big feature branch on main and see that is the last common commit now

   git rebase main
   echo "Last common commit: " `git merge-base my-big-feature main`
   git --no-pager log --format=oneline

8. Return to the default branch and delete the my-big-feature one

   git checkout -
   git branch -D my-big-feature

Now the last default branch's commit is the last common commit for the feature and the default branches.

---

Keeping the branch lean

1. Create new branch

   git checkout -b lean-branch

2. Add the first commit

   touch code.txt
   echo "My feature code" > code.txt
   git add code.txt
   git commit -m "feat: cool feature"

3. Add the second commit

   touch tests.txt
   echo "My feature tests" > tests.txt
   git add tests.txt
   git commit -m "tests: cool feature"
   git --no-pager log --format=oneline

4. OMG! You've run tests and figured out that there is a bug. Fix it!

   echo "My feature fixed code" > code.txt

5. Insert the fix into the first commit so nobody will know we had bugs.

   git add code.txt
   git commit --fixup HEAD~1
   git --no-pager log --format=oneline

Note: You can use the commit sha instead of HEAD~X.

6. Now we need to rebase commits.

   git rebase -i --autosquash HEAD~3

Press ESCAPE and :q! in the vim editor.

7. What do we have now?

   git --no-pager log --format=oneline

Note: If you pushed the changes to the upstream after rebase you have to use git push --force to replace fixed commits.

Conclusion

Rebase helps to keep the branch both up-to-date and clean, w/o any extraneous commits. Using interactive rebase we can fixup every commit in our branch even if there are others on top of it. We can rename and drop commits and even to change the order.

Choose REBASE!
Keep your PR tidy!