Explain git rebase code

What this git rebase sample shows

pick, fixup and squash

Each line is one commit, oldest first, and git runs them from the top. pick keeps a commit as it is. The 2 fixup lines folded wip and fix typo into Add discount codes and kept only that commit's message, so the debug lines wip added and fix typo took out left no trace. With squash for wip and the other lines left as pick, git opened the message editor with both messages, Add discount codes and wip, for you to combine.

reword and drop

reword kept the change and stopped for a new message: Use discount in checkout became Apply discount codes at checkout. drop removed the Add gitignore commit, and its .gitignore file with it. The branch went from 5 commits to 2, and git printed Successfully rebased and updated refs/heads/feature/discounts.

new hashes and the push

A rebase writes new commits: the 2 left were 0076ae5 and 1279aa9, and none of the old hashes was on the branch any more. The copy on the remote still pointed at the old tip, 803b36d, so a plain git push was rejected as non-fast-forward. git push --force-with-lease replaced it, and printed forced update.

reordering

Lines can be moved, and git applies them in the new order. With fix typo moved above wip, the rebase stopped at fix typo with The previous cherry-pick is now empty, because the debug lines it takes out weren't there yet, and exited with code 1. git rebase --abort put the branch back to all 5 commits.

Good to know

• Run with git 2.55.0 on Linux in a test repo: main with one commit, and a feature/discounts branch of 5 commits by a test author. GIT_SEQUENCE_EDITOR supplied the edited todo list and GIT_EDITOR the new message, in place of an editor window. The todo list above is the one git wrote, with the 5 commands edited and 17 of its 30 help lines left out.
• Deleting every line stopped the rebase with error: nothing to do and left all 5 commits as they were.

Watch out: Deleting a line drops that commit, and git doesn't ask. With the Add gitignore line deleted instead of marked drop, the rebase printed Successfully rebased, exited with code 0, and .gitignore was gone from the branch. The old commits stay in the repo for a while, and git kept the old tip in ORIG_HEAD, 803b36d here. Because the dropped commit was that tip, git cherry-pick 803b36d brought it back.