What tool should I use to split git commit into multiple ones?

Question

I've coded a feature spanning thousand of modified lines in a project, and now it all ended up in one big commit (I've squashed the work-in-progress commits). Now I'd like to split the changes into multiple commits for easier review/possibly multiple PRs.

Some files contain multiple changes that should end up in different commits, so I am looking for a WYSIWIG editor using three-pane view, that would allow me to move some lines to the intermediate commit while seeing the previous and future version (+ some manual changes). I use IntelliJ IDEA for the development, so I imagine something similar to conflict resolution dialog.

I could switch to different branch/tag the single-commit version and do Git->Compare with Branch (and grab the changes from there), but I am looking for something of more convenience.

While this could be marked as off-topic/opinionated, I believe that a neutral suggestion for a different workflow might be valuable.

Answer 1

For IntelliJ I use this workflow:

• Open the git log window or Alt + 9
• Right click on commit you want to split → Interactively Rebase from Here
• Right click on commit you want to split → Stop to edit or Alt + E
• Start Rebasing
• Right click to the current commit in the git log with the yellow label 🏷️! → Undo commit... alternatively execute git reset HEAD~1 in the terminal
• Ctrl + K to select and commit your changes with the according message. Repeat as often as necessary until all changes are committed.
• On the bottom right click: Rebase Stopped for Editing → Continue

Answer 2

Not sure about a tool that lets you do this, but, as according to the git documentation you can split a commit using the builtin rebase function. Something like:

git rebase -i
...
pick abc1234 the commit I wanna keep
edit 5904fjl THE COMMIT I WANT TO SPLIT
pick alkj022 my latest commit to keep

After that run git reset HEAD^ and you can manually break out your changes into commits. You can use the git add --patch to more easily split your intra-file changes into commits. Or if your Intellij IDE has a good git GUI you can use that. The splitting, at least in my experience, has to be done from the command line.