When you click the default Merge pull request option on a pull request on GitHub, all commits from the feature branch are added to the base branch in a merge commit. The pull request is merged using the
To merge pull requests, you must have write permissions in the repository.
When you select the Squash and merge option on a pull request on GitHub, the pull request's commits are squashed into a single commit. Instead of seeing all of a contributor's individual commits from a topic branch, the commits are combined into one commit and merged into the default branch. Pull requests with squashed commits are merged using the fast-forward option.
You can use squash and merge to create a more streamlined Git history in your repository. Work-in-progress commits are helpful when working on a feature branch, but they aren’t necessarily important to retain in the Git history. If you squash these commits into one commit while merging to the default branch, you can retain the original changes with a clear Git history.
When you squash and merge, GitHub generates a commit message which you can change if you want to. The message default depends on whether the pull request contains multiple commits or just one.
|Number of commits||Summary||Description|
|One commit||The title of the commit message for the single commit, followed by the pull request number||The body text of the commit message for the single commit|
|More than one commit||The pull request title, followed by the pull request number||A list of the commit messages for all of the squashed commits, in date order|
If you plan to continue work on the head branch of a pull request after the pull request is merged, we recommend you don't squash and merge the pull request.
When you create a pull request, GitHub identifies the most recent commit that is on both the head branch and the base branch: the common ancestor commit. When you squash and merge the pull request, GitHub creates a commit on the base branch that contains all of the changes you made on the head branch since the common ancestor commit.
Because this commit is only on the base branch and not the head branch, the common ancestor of the two branches remains unchanged. If you continue to work on the head branch, then create a new pull request between the two branches, the pull request will include all of the commits since the common ancestor, including commits that you squashed and merged in the previous pull request. If there are no conflicts, you can safely merge these commits. However, this workflow makes merge conflicts more likely. If you continue to squash and merge pull requests for a long-running head branch, you will have to resolve the same conflicts repeatedly.
When you select the Rebase and merge option on a pull request on GitHub, all commits from the topic branch (or head branch) are added onto the base branch individually without a merge commit. Pull requests with rebased commits are merged using the fast-forward option.
The rebase and merge behavior on GitHub deviates slightly from
git rebase. Rebase and merge on GitHub will always update the committer information and create new commit SHAs, whereas
git rebase outside of GitHub does not change the committer information when the rebase happens on top of an ancestor commit. For more information about
git rebase, see the "Git rebase" chapter from the Pro Git book.
For a visual representation of
git rebase, see The "Git Branching - Rebasing" chapter from the Pro Git book.
You aren't able to automatically rebase and merge on GitHub when:
- The pull request has merge conflicts.
- Rebasing the commits from the base branch into the head branch runs into conflicts.
- Rebasing the commits is considered "unsafe," such as when a rebase is possible without merge conflicts but would produce a different result than a merge would.
If you still want to rebase the commits but can't rebase and merge automatically on GitHub you must:
- Rebase the topic branch (or head branch) onto the base branch locally on the command line
- Resolve any merge conflicts on the command line.
- Force-push the rebased commits to the pull request's topic branch (or remote head branch).
Anyone with write permissions in the repository, can then merge the changes using the rebase and merge button on GitHub.