How do you explain the difference between 'git merge' and 'git rebase'? What is the Golden Rule of Rebasing?

Both commands integrate changes from one branch into another, but they do it in fundamentally different ways:

• git merge:
  • Combines the histories by executing a three-way merge and creating a new merge commit (if not fast-forward).
  • Pros: Preserves the complete, chronological history of what happened and when. Non-destructive.
  • Cons: Can result in a cluttered history graph with many overlapping merge lines.
• git rebase:
  • Moves the entire base of the feature branch to begin at the tip of the target branch, effectively rewriting history. It plays back commits one-by-one onto the new base.
  • Pros: Results in a perfectly clean, linear history graph without unnecessary merge commits.
  • Cons: Rewrites history. Golden Rule of Rebasing: Never rebase branches that have been pushed to a public/shared repository, as it corrupts collaborators' local histories.

Initial State:
      A---B---C  (main)
           \
            D---E  (feature)
After git merge main into feature:
      A---B---C  (main)
           \   \
            D---E---F  (feature, F is a merge commit)
After git rebase main on feature:
      A---B---C  (main)
               \
                D'---E' (feature, commits D and E are rewritten)