Resolving merge conflicts and undoing a bad commit already pushed to a shared branch (revert vs reset + force-push)

# Conflict markers in the file:
<<<<<<< HEAD
private static final BigDecimal TRANSFER_FEE = new BigDecimal("25.00");
=======
private static final BigDecimal TRANSFER_FEE = new BigDecimal("30.00");
>>>>>>> feature/new-fee-structure

# Between <<<<<<< and ======= is YOUR branch's version
# Between ======= and >>>>>>> is the INCOMING branch's version

# Step 1: Attempt the merge (conflict occurs)
git merge feature/new-fee-structure
# CONFLICT (content): Merge conflict in TransferService.java

# Step 2: Open the file and resolve
# Choose one side, the other, or combine them
# Remove the <<<<<<<, =======, and >>>>>>> markers

# Step 3: Stage the resolved file
git add src/main/java/com/bank/service/TransferService.java

# Step 4: Complete the merge
git commit

# Step 5: Run tests! A syntactically clean resolution can be logically wrong
mvn test

# If the merge goes badly, abort and start over:
git merge --abort

// Resolved file (combining both changes):
private static final BigDecimal TRANSFER_FEE = new BigDecimal("30.00");
// Chose the new fee structure, confirmed with the product team

# Soft reset: undo the commit, keep changes staged
git reset --soft HEAD~1

# Mixed reset (default): undo the commit, keep changes unstaged
git reset HEAD~1

# Hard reset: undo the commit, discard all changes
git reset --hard HEAD~1
# WARNING: hard reset loses uncommitted work

# Revert a single bad commit
git revert abc1234
# Opens editor with: Revert "Add broken fee calculation"
# Creates a NEW commit that undoes abc1234

# Revert a merge commit (specify which parent to keep)
git revert -m 1 abc1234
# -m 1 means keep the first parent (usually main)

# Everyone can pull normally -- no divergence
git push origin develop

# Timeline of disaster:
# 1. You push commit X to shared develop
# 2. Teammates Rajesh and Priya pull, their clones have X
# 3. You reset to before X and force-push
# 4. Remote develop no longer has X
# 5. Rajesh's next pull: conflict or auto-merge that re-introduces X
# 6. Priya pushes her work: X comes back from her clone
# 7. Work can be silently lost

# The "deleted" commit keeps coming back because
# other clones still have it

# WRONG: Reset and force-push a shared branch
git reset --hard HEAD~1
git push --force origin develop
# Every teammate is now divergent!

# CORRECT: Revert adds an inverting commit
git revert abc1234
git push origin develop
# Everyone pulls normally, no divergence

# Safe: force-push your own feature branch
# --force-with-lease refuses if someone else pushed
git push --force-with-lease origin feature/my-branch

# Protected branches should disable force-push entirely
# GitHub: Settings > Branches > Branch protection rules
# [x] Do not allow force pushes

// WRONG: Syntactically resolved but logically broken
// Branch A added: validateBalance(fromAccount, amount);
// Branch B added: applyFee(amount);
// Resolved as:
validateBalance(fromAccount, amount);
applyFee(amount);
// But the fee should be applied BEFORE validation!
// Always run tests after resolving conflicts.