Flatten commits on a branch

Question

Is it possible to condense the commits on a branch into a single commit prior to merging with the main? I thought this would be a fairly common scenario, but maybe I am not using the right search terms.

I'll explain the scenario in more detail. Often I would want to make many local commits while working on a change in a branch to ensure I have a comprehensive history of changes. But once through with the changes in the branch, when I am merging to main, I would like to reduce the commits on the branch to a single one and then merge it to main. I do understand that commits are inexpensive in Git, but in some situations, I might just prefer to do this.

*   merge to main
|\
* | commit 2 on main
* | commit 1 on main
| * commit 2 on branch
| * commit 1 on branch
|/
*   branch from main

to be made to look like

*   merge to main
|\
* | commit 2 on main
* | commit 1 on main
| * commit on branch (branch commits flattened to one)
|/
*   branch from main

I'm a novice when it comes to git. If I have erred in the use of terms, I do apologise.

Answer 1

I would recommend learning to use the interactive rebase, but in case it seems too complicated to you, you can simply use

git reset --soft <diverging-commit>

to undo all commits up to the diverging point without changing the index, and

git commit -s

to make a single commit of all the changes.

Answer 2

Use interactive rebasing. Find the commit where your branch diverged from master (may using git merge-base; let's call the commit <diverge>), then

git rebase -i <diverge>

and an editor will pop up, allowing you to rewrite history interactively. You'll want to squash commits.

Answer 3

You can also use git merge --squash <branch> to merge a branch without performing any commits:

$ git checkout master
$ git merge --squash mybranch
...
Squash commit -- not updating HEAD
Automatic merge went well; stopped before committing as requested
$ git commit

(Update: Removed link to article advocating avoidance of history rewriting. I now think squashing small feature branches prior to review is a good practice.)