How to unmerge a PR/commit on Github ?

Unmerging a pull request or commit on GitHub can be a delicate operation, especially if the changes have already been pushed to a shared branch. However, there are several approaches you can take depending on your specific situation and preferences. Let's explore the options available and walk through the process step-by-step.


### Key Points to Consider


1. There are multiple ways to unmerge a PR/commit, ranging from simple to complex.

2. The choice of method depends on whether you've already pushed the changes and who has access to the repository.

3. Some methods preserve the commit history, while others rewrite history.

4. It's crucial to communicate with your team before taking any action.


### Method 1: Using GitHub's Built-in Revert Feature


GitHub provides a built-in feature to revert a pull request after it has been merged.


1. Go to your repository on GitHub.

2. Click on "Pull requests" tab.

3. Select the pull request you want to revert.

4. Click on "Revert" button near the bottom of the page.

5. Confirm the revert action.


This method creates a new pull request that contains one revert of the merge commit from the original merged pull request [2].


### Method 2: Using Git Commands Locally


If you have local access to the repository, you can use Git commands to unmerge the changes.


1. Fetch the latest changes from the remote repository:

   ```

   git fetch origin

   ```


2. Create a new branch based on the latest state of the target branch:

   ```

   git checkout -b revert-branch origin/main

   ```


3. Find the commit hash of the merge you want to revert:

   ```

   git log --oneline

   ```


4. Revert the merge using the `-m` option:

   ```

   git revert -m 1 <merge-commit-hash>

   ```


5. Push the revert changes to the remote repository:

   ```

   git push origin revert-branch

   ```


This method preserves the commit history and allows for easy rollback if needed [1].


### Method 3: Using Git Reset (for Local Changes Only)


If you haven't pushed the changes yet and only have local modifications, you can use `git reset`:


1. Make sure you're on the branch you want to reset:

   ```

   git checkout <branch-name>

   ```


2. Find the commit hash of the commit before the unwanted merge:

   ```

   git log --oneline

   ```


3. Reset the branch to the desired commit:

   ```

   git reset --hard <commit-hash>

   ```


4. Force push the changes to the remote repository:

   ```

   git push -f origin <branch-name>

   ```


Be cautious with this method as it rewrites history and can cause issues for collaborators [3].


### Method 4: Using GitHub CLI


If you prefer using the command line interface, GitHub CLI offers a convenient way to revert pull requests:


1. Install GitHub CLI if you haven't already.


2. Authenticate with GitHub:

   ```

   gh auth login

   ```


3. List your repositories:

   ```

   gh repo list

   ```


4. Select the repository you want to modify.


5. View pull requests:

   ```

   gh pr list

   ```


6. Revert a specific pull request:

   ```

   gh pr revert <pr-number>

   ```


This method combines the simplicity of GitHub's web interface with the power of command-line operations [4].


### Best Practices


1. **Communication**: Always inform your team before attempting to unmerge changes, especially if you're using methods that rewrite history.


2. **Backup**: Before performing any operation that modifies history, create a backup branch:

   ```

   git branch backup-branch

   ```


3. **Use Reverts Instead of Resets**: Prefer `git revert` over `git reset` when dealing with shared branches to maintain a clear history of changes.


4. **Avoid Force Pushes**: Unless absolutely necessary, try to avoid force pushing to shared branches to prevent conflicts with other contributors.


5. **Review Changes**: Before applying any unmerge operation, carefully review the changes to ensure you're not losing important work.


### Troubleshooting Tips


1. **Merge Conflicts**: If reverting a pull request causes merge conflicts, you may need to resolve them manually.


2. **History Preservation**: Methods like `git revert` preserve the commit history, which can be beneficial for auditing purposes.


3. **Team Coordination**: If multiple team members have already integrated the changes, coordinate with them to avoid confusion.


4. **Rollback Plan**: Have a plan ready for rolling back changes if the unmerge operation doesn't go as expected.


### Summary


Unmerging a PR/commit on GitHub can be achieved through various methods, ranging from simple GitHub web interface actions to complex Git command sequences. The choice of method depends on factors such as whether you've already pushed the changes, who has access to the repository, and your preference for preserving history.


Key considerations include:

- Preserving commit history vs rewriting history

- Impact on collaborators

- Ease of use and reversibility

- Potential for merge conflicts


Regardless of the method chosen, clear communication with your team is crucial to avoid confusion and potential conflicts. Always review changes carefully before applying any unmerge operation, and have a rollback plan in place for added safety.


Remember, while these methods can effectively unmerge changes, they should be used judiciously. In many cases, it's better to address issues within the pull request itself before merging, or to discuss and agree on changes before committing them to shared branches.

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