Understanding What Happens When You Rebase a Pushed Commit in Git

Описание: Learn how rebasing a commit that has already been pushed to a development branch in Git impacts your commit history and changes the collaboration dynamics with remote repositories.
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Understanding What Happens When You Rebase a Pushed Commit in Git

Git is a powerful tool for managing changes in source code, allowing multiple users to collaborate seamlessly. However, with great power comes great responsibility; especially when it comes to operations like rebasing. One common scenario that new Git users encounter is what happens when they try to rebase a commit that has already been pushed to a development branch. In this guide, we will explore this question in detail, breaking down the process to ensure clarity and understanding.

The Scenario: Committing Locally and Pushing to Remote

Let's set the stage. Assume you are working on a local Git repository, and your commits look something like this:

[[See Video to Reveal this Text or Code Snippet]]

Where:

A, B, and C are commits that were in both the local master and the remote origin/master.

X is your new commit that you've added to your local master.

Commits D, E, and F have been added to origin/master by other collaborators.

The Question

After making your changes, you attempt to re-align your local master with the remote origin/master. You run the command:

[[See Video to Reveal this Text or Code Snippet]]

Now, the question arises:

Will your commit X be moved to the tip of the master, or will it stay put because it's already been pushed to the remote repository?

What Happens When You Rebase

When you run the command git pull --rebase origin master, here's what happens:

Fetching Changes: Git will first fetch the changes from origin/master, which contains commits D, E, and F.

Replaying Commits: The commit X that exists in your local master will be "replayed" on top of the fetched updates (F in this case). A new commit ID is generated for this rebased commit, typically noted as X'.

Updated Commit Graph

After the command, the commit history will look like this:

[[See Video to Reveal this Text or Code Snippet]]

Here, X has been transformed into X', reflecting that it has been rebased on top of the latest changes from origin/master.

What If I’ve Already Pushed My Commit?

Now, let's consider your situation where you’ve already pushed commit X to origin/master.

The state of your commit history before running git pull --rebase looks like:

[[See Video to Reveal this Text or Code Snippet]]

If other team members had already pushed their commits D, E, and F after you pushed X, the graph becomes:

[[See Video to Reveal this Text or Code Snippet]]

Running the git pull --rebase origin master command again here would yield similar results to:

[[See Video to Reveal this Text or Code Snippet]]

This means that Git sees your commit X as already part of origin/master, and it will not be replayed again on top of D, E, and F.

Final Commit Graph After Rebase

Your commit graph would now look like this:

[[See Video to Reveal this Text or Code Snippet]]

In this case, X is simply part of the past history; it was already included in the remote repository and won't be duplicated.

Conclusion

Understanding how rebasing works in Git is crucial to maintaining an orderly and conflict-free code repository. When you rebase commits that have already been pushed to a remote branch:

If there are new changes in the remote, your commits will be replayed on top of those changes, creating new commit IDs.

If your commits are already part of the remote history, Git will not replay them again.

Rebasing can be a little tricky at first, but with practice and patience, it will become a valuable part of your Git toolkit. Happy coding!