Scenario 2 — Merge Conflict Drill

# Scenario 2 — Merge Conflict Drill ## The brief Create a scenario where two branches conflict; practice the full resolution flow. Until you've done this 5+ times, conflicts feel scary. After: routine. ## Step 1: Setup (10 min) ```bash mkdir conflict-drill && cd conflict-drill git init echo "Hello, world" > greeting.txt git add . && git commit -m "Initial: greeting" ``` Now create the conflict scenario: ```bash # Make branch A git switch -c branch-a echo "Hi, world!" > greeting.txt # change "Hello" to "Hi" git commit -am "branch-a: friendlier greeting" # Make branch B (from main) git switch main git switch -c branch-b echo "Hello, world!" > greeting.txt # add an exclamation mark git commit -am "branch-b: add exclamation" git log --all --oneline --graph # Should show two branches diverging from main ``` ## Step 2: Provoke the conflict (10 min) ```bash git switch main git merge branch-a # fast-forward; main moves to branch-a's tip git merge branch-b # CONFLICT # Auto-merging greeting.txt # CONFLICT (content): Merge conflict in greeting.txt # Automatic merge failed; fix conflicts and then commit the result. ``` Check status: ```bash git status # Unmerged paths: # both modified: greeting.txt ``` ## Step 3: Inspect and resolve (15 min) ```bash cat greeting.txt # >>>>>> branch-b ``` Edit greeting.txt. Decide: - Keep HEAD ("Hi, world!") → delete bottom + markers. - Keep branch-b ("Hello, world!") → delete top + markers. - Combine ("Hi, world!!!") → custom edit. Try each: ```bash # Version 1: keep mine (HEAD) echo "Hi, world!" > greeting.txt git add greeting.txt git status # should show clean staging git commit # finalize ``` Then `git reset --hard HEAD~1` to undo and try again. ## Step 4: Three-way conflict (with `diff3`) Enable diff3 to see the base: ```bash git config --global merge.conflictstyle diff3 ``` Reset and try again: ```bash git reset --hard branch-a-merged-commit # back to after first merge git merge branch-b cat greeting.txt # >>>>>> branch-b ``` Now you see what each side CHANGED from the base — better basis for resolution. ## Step 5: Abort vs continue Practice aborting mid-merge: ```bash git merge --abort # Restores pre-merge state git status # clean ``` ## Step 6: Multi-file conflict (15 min) Make it more realistic — two files conflicting: ```bash git switch main git reset --hard git switch branch-a echo "Welcome!" > greeting.txt echo "v2" > version.txt git commit -am "branch-a: v2" git switch branch-b echo "Howdy!" > greeting.txt echo "v3" > version.txt git commit -am "branch-b: v3" git switch main git merge branch-a git merge branch-b # Two conflicts! git status # Unmerged paths: # both modified: greeting.txt # both modified: version.txt ``` Resolve both: ```bash vim greeting.txt # edit git add greeting.txt vim version.txt # edit git add version.txt git commit # finalize ``` ## Step 7: Rebase with conflicts Rebase brings conflicts one commit at a time: ```bash git reset --hard git switch branch-b git rebase branch-a # Conflict on each commit; resolve and continue git add file.txt git rebase --continue ``` If stuck: `git rebase --abort`. ## Deliverables - Show you can do the full cycle: provoke conflict → resolve → commit → verify. - A `NOTES.md` describing: - The conflict marker structure (HEAD/base/incoming). - The 3-step resolution flow (edit, add, commit). - How `--abort` saves you. - Difference between merge conflict and rebase conflict. ## What you'll learn - The mechanics of merge conflicts. - Reading conflict markers. - The resolve-add-commit flow. - `diff3` style for ancestor context. - `--abort` as your safety net. - Multi-file conflict handling. ## Stretch - Use a merge tool (`git mergetool` or VS Code). - Practice with binary files (different image versions). - Try `git rerere` (reuse recorded resolution) for repeat conflicts.