5. Merging & Conflict Resolution

Fast-forward merge (no divergence)

git switch main
git merge feature/login      # if main hasn't moved, HEAD just advances

3-way merge (branches diverged)

git merge feature/login      # creates a merge commit
git merge --no-ff feature/login   # always create merge commit (preserves history)
git merge --squash feature/login  # squash all branch commits into one staged change

Resolving conflicts

When Git can't auto-merge, you see conflict markers:

<<<<<<< HEAD
    return user.isAdmin;
=======
    return user.role === 'admin';
>>>>>>> feature/role-check

Steps to resolve:

# 1. See which files conflict
git status

# 2. Edit each conflicted file — remove markers, keep the right code

# 3. Mark resolved
git add path/to/file.txt

# 4. Complete the merge
git commit

# OR abort entirely
git merge --abort

Merge tool:

git mergetool          # opens configured visual diff tool
git config --global merge.tool vscode

Merge vs Rebase — when to use each

Situation	Prefer
Shared/public branch	Merge (preserves history)
Local cleanup before PR	Rebase (linear history)
Main ← feature	Merge
feature ← updated main	Rebase (keep feature up-to-date)

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