How to undo a fixup commit if it was created by mistake?

Undoing a Fixup Commit

In the world of Git, a "fixup" commit is a special type of commit that is used to quickly fix or amend a previous commit. It's a handy tool for cleaning up your commit history, but it can also lead to some confusion if you accidentally create one.

If you've accidentally created a fixup commit, don't worry! Git provides a few ways to undo it and restore your commit history to its previous state.

Squashing the Fixup Commit

The most common way to undo a fixup commit is to use the git rebase command to squash the fixup commit back into the original commit. Here's how you can do it:

First, identify the commit that the fixup commit is meant to fix. You can use git log to find the commit hash.
Next, start an interactive rebase by running git rebase -i <commit-hash>^. This will open up an editor with a list of your recent commits.
In the editor, locate the fixup commit and change the word "pick" to "fixup" (or "f" for short) for that commit. This will tell Git to squash the fixup commit into the previous commit.
Save the changes and exit the editor. Git will now rewrite your commit history, squashing the fixup commit into the previous commit.

Here's an example of what the interactive rebase editor might look like:

pick 1a2b3c4 Initial commit
fixup 5e6f7g8 Fix typo
pick 9h0i1j2 Add new feature

In this example, the fixup commit with the hash 5e6f7g8 will be squashed into the previous commit 1a2b3c4.

graph LR A[Initial commit] --> B[Fix typo] B --> C[Add new feature]

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

graph LR A[Initial commit] --> B[Fix typo and add new feature]

Resetting to the Previous Commit

If you don't want to squash the fixup commit, you can also reset your repository to the commit before the fixup commit was made. Here's how:

First, identify the commit that the fixup commit is meant to fix, just like in the previous example.
Next, run git reset --hard <commit-hash>^. This will reset your repository to the commit before the fixup commit, effectively undoing the fixup commit.

Be careful when using git reset --hard, as it will discard all uncommitted changes in your working directory. Make sure to stash or commit any changes you want to keep before running this command.

graph LR A[Initial commit] --> B[Fix typo] B --> C[Add new feature] C -- Fixup commit --> D[Add new feature]

After running git reset --hard <commit-hash>^, your commit history will look like this:

graph LR A[Initial commit] --> B[Fix typo] B --> C[Add new feature]

In both of these examples, the key is to identify the commit that the fixup commit is meant to fix, and then use Git's powerful rewriting capabilities to undo the fixup commit and restore your commit history to its previous state.

Remember, undoing a fixup commit is a common task in Git, and it's important to understand how to do it correctly to maintain a clean and organized commit history for your project.