Git Merge vs. Rebase

Both git merge and git rebase solve the same problem: integrating changes from one branch into another. However, they do so in distinct ways, and choosing the right one depends on your team's workflow and goals for the project history.

Git Merge

git merge is a non-destructive operation. It takes the commits from your feature branch and the commits from the target branch (e.g., main) and combines them.

When you merge a feature branch into main, it creates a new merge commit in the main branch. This commit has two parents: one from the main branch and one from the feature branch, creating a diamond shape in your commit history.

      A---B---C feature
     /         \
D---E---F---G---H main

In this diagram, H is the merge commit.

When to use git merge:

1. Merging into Public Branches: Always use merge when integrating a completed feature branch into a shared public branch like main or develop. This preserves the context of the branch and keeps the history of what actually happened.
2. Preserving History: If you want a precise and explicit history of when features were branched and merged, merge is the right tool. It shows the parallel development of different features.
3. Team Collaboration: It's generally safer for teams, especially those with members new to Git, as it doesn't rewrite commit history.

Pros:

• Simple and straightforward.
• Preserves the original commit history as it happened.
• Avoids rewriting commits that may be shared with others.

Cons:

• Can create a cluttered, non-linear history that is hard to read.
• The log can be polluted with many "Merge branch 'feature-x'" commits.

Git Rebase

git rebase moves the entire feature branch to begin on the tip of the target branch (e.g., main). It rewrites project history by creating new commits for each commit in the original branch.

This results in a perfectly linear history, making it look as though the feature was developed sequentially after the latest changes on main.

                  A'--B'--C' feature
                 /
D---E---F---G---H main

Here, A', B', and C' are new commits that mirror the changes of A, B, and C.

When to use git rebase:

1. Updating a Private Feature Branch: Use rebase to incorporate the latest changes from main into your local, un-pushed feature branch. This keeps your branch up-to-date and helps avoid complex merge conflicts later.
2. Cleaning Up History: Before creating a pull request, you can use interactive rebase (git rebase -i) to clean up your local commits—squashing, editing, or reordering them to create a clean and logical sequence.

The Golden Rule of Rebasing:

Never rebase a branch that has been pushed and is being used by others.

Rebasing creates new commits and abandons the old ones. If other developers have based their work on your original commits, they will have a diverged history, leading to significant confusion and repository cleanup headaches.

Pros:

• Creates a clean, linear, and easy-to-read commit history.
• Eliminates unnecessary merge commits.

Cons:

• Rewrites history, which is dangerous on shared branches.
• Can be more complex to resolve conflicts, as you may have to resolve them on each replayed commit.
• Loses the context of when the feature branch was originally created.

Summary: Which One Should You Use?

A common and effective workflow is to use rebase for cleanup and updating, and merge for integration:

• While developing on your local feature branch: Use git rebase main to pull in the latest updates from the main branch. This keeps your feature branch current and your history linear.
• When your feature is complete: Merge your feature branch into main using a standard git merge (often done via a pull request). This creates a single merge commit, preserving the history of the feature as a single unit of work.

This hybrid approach gives you the best of both worlds: a clean, linear history within your feature branches and a reliable, non-destructive merge process for integrating them into the main codebase.