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)

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:

# 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)

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:

git status
# Unmerged paths:
#   both modified: greeting.txt

Step 3: Inspect and resolve (15 min)

cat greeting.txt
# <<<<<<< HEAD
# Hi, world!
# =======
# Hello, world!
# >>>>>>> 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:

# 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:

git config --global merge.conflictstyle diff3

Reset and try again:

git reset --hard HEAD~1  # back to after first merge (main was at branch-a's tip)
git merge branch-b
cat greeting.txt
# <<<<<<< HEAD
# Hi, world!
# ||||||| base
# Hello, world
# =======
# Hello, world!
# >>>>>>> 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:

git merge --abort
# Restores pre-merge state
git status                          # clean

Step 6: Multi-file conflict (15 min)

Make it more realistic — two files conflicting:

git switch main
git reset --hard HEAD~1  # the commit before the multi-file merge

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:

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:

git reset --hard HEAD~1  # the commit before the rebase
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

Submission contract: upload NOTES.md (conflict-marker anatomy, the edit→add→commit flow, how --abort saves you, merge-vs-rebase conflict difference).

100-pt rubric: provoke + resolve a conflict end-to-end (25) / diff3 base shown and used (20) / --abort demonstrated (15) / multi-file conflict resolved (25) / rebase conflict resolved (15).

upload NOTES.md (conflict-marker anatomy, the edit→add→commit flow, how --abort saves you, merge-vs-rebase conflict difference).

provoke + resolve a conflict end-to-end (25) / diff3 base shown and used (20) / --abort demonstrated (15) / multi-file conflict resolved (25) / rebase conflict resolved (15).