Fast-forward merge in Git - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is a fast-forward merge in Git?

Which statement best describes a fast-forward merge in Git?

A It deletes the source branch after merging automatically.

B It creates a new merge commit even if the branches have no divergent changes.

C It moves the branch pointer forward without creating a new commit when there are no divergent changes.

D It rewrites the commit history to remove merge commits.

💡 Hint

Think about what happens when the target branch has no new commits since branching.

A fast-forward merge simply moves the branch pointer forward to the latest commit if there are no divergent changes, avoiding a merge commit.

💻 Command Output

intermediate

Output of fast-forward merge command

Given the following Git commands executed in order, what is the output of the final git merge feature command?

git checkout main
# main points to commit A

git checkout -b feature
# feature branch created from A

git commit --allow-empty -m "Add feature"
# feature now points to commit B

git checkout main

git merge feature

A Merge made by the 'recursive' strategy.

B error: You have unmerged paths.

C Already up to date.

D

Updating A..B
Fast-forward

💡 Hint

Consider if the main branch has new commits after branching.

Since main has no new commits after branching, the merge is a fast-forward and Git outputs 'Updating A..B' and 'Fast-forward'.

🔀 Workflow

advanced

When does Git refuse a fast-forward merge?

Which situation will cause Git to refuse a fast-forward merge by default?

A When the target branch has new commits not in the source branch.

B When the branches are identical.

C When the source branch is ahead and no new commits exist on the target branch.

D When the source branch is behind the target branch.

💡 Hint

Think about what happens if both branches have new commits.

If the target branch has new commits not in the source branch, Git cannot fast-forward and will create a merge commit or refuse fast-forward if configured.

❓ Troubleshoot

advanced

Why does 'git merge --ff-only' fail?

You run git merge --ff-only feature but get the error: fatal: Not possible to fast-forward, aborting. What is the most likely cause?

A The feature branch is fully merged already.

B The target branch has commits that the feature branch does not have.

C You have uncommitted changes in your working directory.

D The feature branch does not exist.

💡 Hint

Consider what --ff-only means for the merge.

The --ff-only option refuses to create a merge commit. If the target branch has commits not in the feature branch, fast-forward is impossible and Git aborts.

✅ Best Practice

expert

Choosing merge strategy for a clean history

You want to keep your Git history linear and clean without merge commits. Which command ensures merges only happen if they can fast-forward?

A git merge --ff-only feature

B git merge --no-ff feature

C git merge --squash feature

D git merge --no-commit feature

💡 Hint

Think about which option prevents merge commits.

The --ff-only option refuses to create merge commits and only merges if a fast-forward is possible, keeping history linear.