How do I squash my last N commits together?

Squashing commits in Git refers to the process of combining multiple consecutive commits into a single commit. This technique is particularly useful for cleaning up your project's history before merging feature branches into the main branch, ensuring that the commit history remains concise and meaningful. Whether you're tidying up a series of minor commits or consolidating work before a pull request, squashing commits enhances the readability and maintainability of your repository.

This comprehensive guide will walk you through the steps to squash your last N commits together using Git's interactive rebase feature. Additionally, it will cover alternative methods, important considerations, and best practices to ensure a smooth and error-free process.

Prerequisites

Before proceeding, ensure that:

• Git is Installed: Verify by running:

  git --version

  If not installed, download it from the official Git website.

• Familiarity with Git Basics: Understanding commits, branches, and the staging area will help in executing the commands effectively.

• Backup Important Work: Squashing commits rewrites commit history, which can lead to data loss if not done correctly. If there's any uncertainty, consider creating a backup branch or stashing changes.

  # Create a backup branch
  git branch backup-branch
  
  # Or stash changes
  git stash save "Backup before squashing commits"

Understanding Commit Squashing

What is Commit Squashing?

Commit squashing is the process of merging multiple sequential commits into a single commit. This is typically done to simplify the commit history, making it easier to understand and navigate. Squashing is especially beneficial when:

• Multiple Small Commits: You've made several minor commits (e.g., typo fixes, incremental changes) that don't need to be individually recorded.

• Feature Development: You're developing a feature and want to consolidate all related changes into one commit before merging into the main branch.

• Preparing for Pull Requests: Clean commit history can make code reviews more straightforward and maintainable.

Benefits of Squashing Commits

• Cleaner History: A streamlined commit history enhances readability and makes it easier to track significant changes.

• Easier Reverts: Managing changes becomes simpler when related modifications are grouped together.

• Improved Collaboration: A well-organized commit history facilitates better collaboration among team members.

Caveats

• Rewriting History: Squashing alters the commit history. If the commits have been pushed to a shared remote repository, it can cause conflicts for collaborators.

• Loss of Detailed History: Combining commits can obscure the step-by-step progression of changes, potentially making debugging more challenging.

Method 1: Using Interactive Rebase

Interactive rebase is the most common and flexible method for squashing commits. It allows you to reorder, squash, or edit commits as needed.

Steps to Squash the Last N Commits

Assuming you want to squash the last N commits into a single commit:

1. Determine the Number of Commits to Squash

   Decide how many recent commits you want to squash. For example, to squash the last 3 commits:

   N=3

2. Initiate Interactive Rebase

   Start an interactive rebase session targeting the last N commits:

   git rebase -i HEAD~N

   Replace N with the number of commits you wish to squash. Using our example:

   git rebase -i HEAD~3

3. Modify the Rebase Todo List

   An editor will open displaying a list of commits:

   pick e3a1b35 Commit message for commit 1
   pick f7c2d89 Commit message for commit 2
   pick 8c4d2a1 Commit message for commit 3
   

   To squash the last two commits into the first one:

   pick e3a1b35 Commit message for commit 1
   squash f7c2d89 Commit message for commit 2
   squash 8c4d2a1 Commit message for commit 3
   

   • Commands:
     • pick: Use the commit as-is.
     • squash (or s): Combine this commit with the previous one.

   Alternative Approach: If you want to keep the first commit as-is and squash the subsequent commits into it.

4. Save and Close the Editor

   After modifying the commands, save the file and exit the editor. Git will proceed with the rebase.

5. Edit the Commit Message

   A new editor window will appear, allowing you to edit the combined commit message. You can:

   • Keep one of the existing messages.
   • Combine messages.
   • Write a new, descriptive message.

   Example Combined Commit Message:

   Commit message for commit 1
   
   # This is a combination of 3 commits.
   # The first commit's message is:
   Commit message for commit 1
   
   # This is the 2nd commit message:
   
   Commit message for commit 2
   
   # This is the 3rd commit message:
   
   Commit message for commit 3
   

   Modify as needed, then save and close the editor.

6. Finalize the Rebase

   Git will apply the squashed commit. If there are no conflicts, the rebase will complete successfully.

7. Verify the Commit History

   Check the commit history to ensure that the commits have been squashed:

   git log --oneline

   Expected Output:

   a9c8d7e Combined commit message for the last 3 commits
   b2c3d4e Previous commit
   ...
   

Handling Conflicts

If Git encounters conflicts during the rebase:

1. Resolve the Conflicts Manually

   Open the conflicted files, resolve the issues, and save the changes.

2. Stage the Resolved Files

   git add <file-path>

3. Continue the Rebase

   git rebase --continue

4. Abort the Rebase (If Necessary)

   If the rebase becomes too complex or you decide not to proceed:

   git rebase --abort

   This will return your branch to its state before initiating the rebase.

Method 2: Using git reset and git commit

An alternative method to squash commits involves using git reset to unstage commits and then creating a new commit. This approach is less flexible than interactive rebase but can be quicker for simple scenarios.

Steps to Squash the Last N Commits

1. Soft Reset to the Target Commit

   Use git reset with the --soft flag to move HEAD back by N commits while keeping changes staged.

   git reset --soft HEAD~N

   Example: To squash the last 3 commits:

   git reset --soft HEAD~3

2. Create a New Commit

   Combine the staged changes into a single commit.

   git commit -m "Combined commit message for the last 3 commits"

3. Verify the Commit History

   git log --oneline

   Expected Output:

   a9c8d7e Combined commit message for the last 3 commits
   b2c3d4e Previous commit
   ...
   

Notes

• No History Rewriting Beyond the Last N Commits: This method only affects the last N commits.

• Preserves Changes: Unlike git reset --hard, --soft preserves your changes in the staging area, allowing you to create a new commit.

• Less Granular Control: This method doesn't allow you to selectively squash specific commits within the last N.

Best Practices and Considerations

1. Backup Before Squashing:

   • Create a Backup Branch:

     git branch backup-branch

   • Or Stash Changes:

     git stash save "Backup before squashing commits"

2. Avoid Squashing Public Commits:

   • Impact on Collaborators: Squashing commits that have been pushed to a shared remote repository can cause conflicts for others who have based work on those commits.

   • Best Practice: Only squash commits that haven't been pushed yet or coordinate with your team if necessary.

3. Use Descriptive Commit Messages:

   • Clarity: Ensure that the combined commit message clearly describes the changes for future reference.

   • Consistency: Maintain a consistent format for commit messages across your project.

4. Regularly Pull and Rebase:

   • Synchronize Changes: Regularly fetch and rebase your branch to stay updated with the remote repository, reducing the likelihood of conflicts during squashing.

   git fetch origin
   git rebase origin/main

5. Understand the Rebase Process:

   • Interactive Rebase: Offers granular control over commits but requires careful handling to avoid unintended history rewriting.

   • Non-Interactive Methods: Faster but less flexible, suitable for straightforward squashing needs.

6. Communicate with Your Team:

   • Inform Collaborators: If you're working in a team, communicate about squashing commits, especially if it involves shared branches.

   • Pull Requests: Utilize pull requests or merge requests to review and manage squashed commits effectively.

7. Leverage Git GUI Tools:

   • Visual Assistance: Tools like GitKraken, SourceTree, or IDE-integrated Git tools can simplify the squashing process with visual interfaces.

Example Scenarios

Scenario 1: Squashing the Last 3 Commits Before Pushing

Objective: You've made three commits with minor changes and want to squash them into a single commit before pushing to the remote repository.

Steps:

1. Check Commit History:

   git log --oneline

   Sample Output:

   a1b2c3d Fix typo in README
   e4f5g6h Update documentation
   f7g8h9i Improve error handling
   d0e1f2g Add unit tests
   

2. Initiate Interactive Rebase for the Last 3 Commits:

   git rebase -i HEAD~3

3. Modify the Rebase Todo List:

   In the editor, change pick to squash (or s) for the second and third commits:

   pick e4f5g6h Update documentation
   squash f7g8h9i Improve error handling
   squash a1b2c3d Fix typo in README
   

4. Save and Close the Editor.

5. Edit the Combined Commit Message:

   Modify the commit message to reflect all changes:

   Update documentation, improve error handling, and fix README typos
   

6. Finalize the Rebase:

   Save and close the editor to complete the rebase.

7. Verify the Commit History:

   git log --oneline

   Expected Output:

   z9y8x7w Combined commit message
   d0e1f2g Add unit tests
   

8. Push the Squashed Commit:

   git push origin your-branch-name

   If the branch hasn't been pushed before, set the upstream:

   git push -u origin your-branch-name

Outcome:

• The three minor commits are now combined into a single, more meaningful commit.
• The commit history is cleaner and easier to understand.

Scenario 2: Squashing Commits After Pushing to Remote

Objective: You've already pushed multiple commits to a remote branch but now wish to squash them into a single commit. This requires careful handling to avoid disrupting the remote history.

Steps:

1. Create a Backup Branch:

   git branch backup-branch

   This preserves the current state in case you need to revert.

2. Initiate Interactive Rebase:

   git rebase -i HEAD~N

   Replace N with the number of commits you want to squash.

3. Modify the Rebase Todo List:

   Change pick to squash for the commits you wish to combine.

4. Finalize the Rebase and Edit Commit Message.

5. Force Push the Squashed Commit:

   Since the commit history has been rewritten, you'll need to force push:

   git push --force origin your-branch-name

   Warning: Force pushing can overwrite remote history and affect other collaborators. Ensure that:

   • You're certain about the changes.
   • No one else has based work on the commits you're altering.
   • Communicate with your team before performing a force push.

Outcome:

• The remote branch now reflects the squashed commit.
• The commit history is cleaner, but collaborators may need to synchronize their local repositories to accommodate the rewritten history.

Scenario 3: Using git reset to Squash Commits

Objective: You prefer using git reset to squash the last 2 commits into one.

Steps:

1. Soft Reset to Two Commits Ago:

   git reset --soft HEAD~2

   This moves HEAD back by two commits, keeping the changes staged.

2. Create a New Squashed Commit:

   git commit -m "Combined commit message for the last 2 commits"

3. Verify the Commit History:

   git log --oneline

   Expected Output:

   z9y8x7w Combined commit message for the last 2 commits
   d0e1f2g Previous commit
   ...
   

4. Push the Squashed Commit:

   git push origin your-branch-name

   If the branch hasn't been pushed before, set the upstream:

   git push -u origin your-branch-name

Outcome:

• The last two commits are now merged into a single commit.
• The commit history is streamlined without multiple minor commits.

Troubleshooting Common Issues

Issue 1: Merge Conflicts During Rebase

Symptom:

During the interactive rebase process, Git encounters conflicts that it cannot resolve automatically.

Solution:

1. Identify Conflicted Files:

   Git will list the files with conflicts.

2. Resolve Conflicts Manually:

   Open each conflicted file, resolve the discrepancies, and save the changes.

3. Stage the Resolved Files:

   git add <file-path>

4. Continue the Rebase:

   git rebase --continue

5. Abort the Rebase (If Necessary):

   If resolving conflicts becomes too complex or you decide not to proceed:

   git rebase --abort

   This will return your branch to its state before initiating the rebase.

Issue 2: Unable to Rebase Multiple Branches

Symptom:

Attempting to squash commits on a branch that has been merged or diverged significantly from the main branch leads to complications.

Solution:

1. Ensure You're on the Correct Branch:

   git checkout your-branch-name

2. Fetch Latest Changes:

   git fetch origin

3. Rebase Onto the Latest Remote Branch:

   git rebase origin/main

4. Proceed with Interactive Rebase:

   git rebase -i HEAD~N

   Replace N with the appropriate number of commits.

Issue 3: Commits Not Squashing as Expected

Symptom:

After performing an interactive rebase, the commits are not combined as intended.

Solution:

1. Verify the Number of Commits:

   Ensure that HEAD~N correctly targets the number of commits you intend to squash.

2. Check the Rebase Todo List:

   Confirm that you've correctly changed pick to squash for the desired commits.

3. Ensure No Additional Commits Are Intervening:

   The commits to be squashed should be consecutive without unrelated commits in between.

4. Review the Commit Messages:

   If the commit messages were not edited properly, Git might retain separate commits. Ensure that you save and close the editor correctly after modifying commit messages.

Additional Resources

• Official Git Documentation:

  • git-rebase
  • git-reset
  • git-log
  • git-commit

• Articles and Tutorials:

  • Atlassian Git Tutorials: Interactive Rebase
  • GitHub Docs: Rewriting History

• Books:

  • Pro Git by Scott Chacon and Ben Straub – A comprehensive resource on Git, available for free online.

• Interactive Learning:

  • Learn Git Branching – An interactive way to visualize and practice Git commands, including rebasing and squashing.

• Git GUI Tools:

  • GitKraken
  • SourceTree
  • Tower

Conclusion

Squashing your last N commits is a powerful technique to maintain a clean and organized Git history. By consolidating multiple commits into a single, coherent commit, you enhance the readability and maintainability of your project's evolution. Whether using interactive rebase for granular control or leveraging git reset for a quicker approach, understanding the mechanics and implications of commit squashing empowers you to manage your repository effectively.

Key Takeaways:

• Interactive Rebase is Versatile: Offers the most control over which commits to squash and how to modify commit messages.

• Always Backup Before Rewriting History: Creating backup branches or stashing changes prevents accidental data loss.

• Be Cautious with Shared Branches: Avoid squashing commits that have been pushed to shared branches unless necessary and coordinated with your team.

• Use Descriptive Commit Messages: After squashing, ensure that the combined commit message accurately reflects all the changes for future reference.

• Leverage Git Tools: Utilize Git GUI clients and interactive learning platforms to deepen your understanding and streamline Git operations.

By adhering to best practices and thoroughly understanding the squashing process, you can maintain a robust and efficient Git workflow that supports both individual development and collaborative projects.