When to rebase and squash commits

This page describes recommendations for when to rebase pull requests and when to combine/squash commits.

When to remove or combine/squash commits

Pull requests must be rebased and at least partially squashed (but not necessarily squashed to a single commit) if large (approximately >10KB) non-source code files (e.g. images, data files, etc.) are added and then removed or modified in the PR commit history (The squashing should remove all but the last addition of the file to not use extra space in the repository).

Combining/squashing commits is encouraged when the number of commits is excessive for the changes made. The definition of ‘excessive’ is subjective, but in general one should attempt to have individual commits be units of change, and not include reversions. As a concrete example, for a change affecting < 10 lines of source code and including a changelog entry, more than a few commits would be excessive. For a larger pull request adding significant functionality, however, more commits may well be appropriate.

As another guideline, squashing should remove extraneous information but should not be used to remove useful information for how a PR was developed. For example, 4 commits that are testing changes and have a commit message of just “debug” should be squashed. But a series of commit messages that are “Implemented feature X”, “added test for feature X”, “fixed bugs revealed by tests for feature X” are useful information and should not be squashed away without reason.

In all cases, be mindful of maintaining a welcoming environment and be helpful with advice, especially for new contributors. E.g., It is expected that a maintainer offer to help a contributor who is a novice git user do any squashing that that maintainer asks for, or do the squash themselves by directly pushing to the PR branch.

When to rebase

Pull requests must be rebased (but not necessarily squashed to a single commit) if at least one of the following conditions is met:

  • There are conflicts with master
  • There are merge commits from upstream/master in the PR commit history (merge commits from PRs to the user’s fork are fine)
  • There are commit messages include offensive language or violate the code of conduct (in this case the rebase must also edit the commit messages)

Github ‘Squash and Merge’ button

We should never use or enable the GitHub ‘Squash and Merge’ button since this creates problems when dealing with identifying backports.