How to squash commits

Why do we need to squash commits

Sometimes when we are working on a feature, we might forget to run all the tests before we commit, and we could get test failures from our CI/CD process in the repository. That’s fine, we can still fix it. But the resulting commit history might not look good, as we should have meaningful commit messages so that it’s easy for someone else to understand what is supposed to change in a particular commit. As projects get bigger and more complex, teams getting larger and people move around quite often, the people fixing the bugs in the future might not have the same knowledge as the one who wrote the piece of code to be examined. So having meaningful commit messages helps people to understand what is supposed to happen.

In the above example, the fix test failure in feature1 and fix linting failure in feature1 can ideally be combined in the commit of feature1, so that someone who needs to add on to feature1 in the future can get a full picture of what are the changes implemented to deliver feature1. This process of combining the commits is known as squashing

How do we do it

There isn’t a git squash command, but we are using git rebase -i <hash before main commit to squash unto>. In the above example, the commit with the message feature1 is the main commit to squash unto, so the hash we need to use is the commit before it, which is the setup. Executing git rebase -i 4f770f6 will open the default editor of your terminal (which is usually the VI editor) to edit the git commands.

The lines starting with # doesn’t matter, as they are just comments and are actually instructions to guide us how to amend the file.

To amend the file in VI, you would need to first go into the Insert mode by pressing i. The default mode when the file is opened is the Command mode, where you can execute the write and exit commands. You’ll notice there bottom of the terminal is showing -- INSERT -- to indicate that you are in the Insert mode.

Then amend the 2 commits you want to squash by changing the pick to squash, as in the screenshot above. The squash commits must follow a pick, so that git knows which commit should these squash commits be squashed onto. So if you try to change the first commit (2f08fef) to squash also, it will result in an error.

Click the Esc key on your keyboard to go back to Command mode, and type :wq (meaning write and quit) to save and exit the VI editor.

Now you will be presented with another VI editor to edit the commits. You can then edit the message to whichever you want it to be. For this example, I’m just going to delete the 2 messages which I don’t need, and keep the original feature1.

After all is done, use git log --oneline to check the commits

As you can see in the above screenshot, we don’t have the unwanted lines anymore.