Answers

Here are the answers to the questions given above:

1. You can use git commit --fixup when creating a bugfix, and then later git rebase --interactive --autosquash before publishing the series.
2. You should not rewrite published history because other developers can do their work based on the version before the changes, and then merging would bring older versions (from before the rewrite) back into existence.
3. Rebase your own changes on top of the new, rebased version of the upstream.
4. If the problem is in the most recent commit, you can amend it with git commit --amend. If you need to rewrite the whole history of the project, you can use the git filter-repo tool. Note, however, the caveat that comes with rewriting published history, namely that it can cause problems for other developers when they will try to integrate their changes.
5. You can use git revert to create the commit that undoes changes brought by an unwanted commit.
6. You can use git notes to add...