Fast-forward merge in Git - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to perform a fast-forward merge of branch 'feature' into 'main'.

Git

git checkout main && git merge [1]

Drag options to blanks, or click blank then click option'

Aclone

Bcommit

Creset

Dfeature

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'commit' or 'reset' instead of the branch name.

Trying to merge without checking out the main branch first.

To fast-forward merge, you merge the feature branch into main using 'git merge feature'.

2fill in blank

medium

Complete the command to update the local branch with a fast-forward merge from the remote 'origin/main'.

Git

git fetch origin && git merge [1]

Drag options to blanks, or click blank then click option'

Aorigin/feature

Borigin/main

Cmain

Dorigin/develop

Attempts:

3 left

💡 Hint

Common Mistakes

Merging a local branch instead of the remote branch after fetch.

Using the wrong remote branch name.

After fetching, merging 'origin/main' updates your local branch with the remote changes using fast-forward if possible.

3fill in blank

hard

Complete the command to perform a fast-forward ONLY merge of branch 'feature' into 'main'.

Git

git checkout main && git merge [1] feature

Drag options to blanks, or click blank then click option'

A--ff-only

B--no-ff

C--ff

Dorigin

Attempts:

3 left

💡 Hint

Common Mistakes

Using '--no-ff' which disables fast-forward merges.

Omitting the option (defaults to fast-forward if possible, but not enforced).

'--ff-only' ensures the merge is fast-forward or fails if not possible. '--no-ff' forces a merge commit even if fast-forward is possible.

4fill in blank

hard

Fill both blanks to create a fast-forward merge command that updates 'main' with 'feature' branch changes.

Git

git checkout [1] && git merge [2]

Drag options to blanks, or click blank then click option'

Amain

Bfeature

Cdevelop

Dmaster

Attempts:

3 left

💡 Hint

Common Mistakes

Switching the order of branches.

Using 'develop' or 'master' instead of 'main' or 'feature'.

You first checkout 'main' branch, then merge the 'feature' branch to fast-forward update.

5fill in blank

hard

Fill all three blanks to perform a safe fast-forward update of 'main' from the remote 'origin'.

Git

git checkout [1] && git fetch [2] && git merge --ff-only [3]

Drag options to blanks, or click blank then click option'

Amain

Borigin

Cfeature

Dorigin/main

Attempts:

3 left

💡 Hint

Common Mistakes

Merging local 'main' instead of 'origin/main'.

Wrong remote name or forgetting fetch.

Using 'feature' instead of 'main' remote.

Checkout 'main', fetch from 'origin', merge 'origin/main' with --ff-only to ensure it's a fast-forward merge or fail.

Practice

1. What happens during a fast-forward merge in Git?

easy

A. The source branch is deleted automatically.

B. A new merge commit is always created.

C. The branch pointer moves forward without creating a new commit.

D. The commit history becomes non-linear.

Solution

1. Step 1: Understand fast-forward merge behavior

   A fast-forward merge moves the branch pointer forward to the latest commit of the source branch without creating a new merge commit.

2. Step 2: Compare with other merge types

   Unlike a normal merge, it does not create a new commit and keeps history linear.

3. Final Answer:

   The branch pointer moves forward without creating a new commit. -> Option C

4. Quick Check:

   Fast-forward merge = pointer moves forward [OK]

Hint: Fast-forward means no new commit, just pointer moves [OK]

Common Mistakes:

• Thinking a merge commit is always created
• Assuming source branch deletes automatically
• Believing history becomes non-linear

2. Which Git command syntax performs a fast-forward merge of branch feature into main only if possible, otherwise aborts?

easy

A. git merge --squash feature

B. git merge feature

C. git merge --no-ff feature

D. git merge --ff-only feature

Solution

1. Step 1: Identify command for fast-forward only

   The option --ff-only tells Git to merge only if it can fast-forward, otherwise it aborts.

2. Step 2: Compare other options

   --no-ff disables fast-forward, --squash creates a single commit without merging, and plain git merge feature may create a merge commit.

3. Final Answer:

   git merge --ff-only feature -> Option D

4. Quick Check:

   Fast-forward only = --ff-only [OK]

Hint: Use --ff-only to ensure only fast-forward merges happen [OK]

Common Mistakes:

• Using --no-ff disables fast-forward merges
• Assuming plain merge always fast-forwards
• Confusing --squash with fast-forward

3. Given the following Git commands, what is the output of git log --oneline main after merging?

git checkout main
# main points to commit A

git checkout -b feature
# feature branch created from A

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

git checkout main

git merge feature

medium

A. B

B. B\nA

C. A

D. Merge commit with A and B

Solution

1. Step 1: Understand branch states before merge

   Main points to commit A. Feature branch adds commit B on top of A.

2. Step 2: Analyze merge behavior

   Since main has no new commits after branching, merging feature into main will fast-forward main to B.

3. Final Answer:

   B\nA -> Option B

4. Quick Check:

   Fast-forward merge moves main to B [OK]

Hint: If main unchanged, merge moves pointer to feature commit [OK]

Common Mistakes:

• Expecting merge commit creation
• Thinking main stays at A
• Confusing commit hashes output

4. You tried to fast-forward merge branch feature into main using git merge --ff-only feature, but Git returned an error. What is the most likely cause?

medium

A. The main branch has new commits not in feature.

B. The feature branch is behind main.

C. The feature branch has no commits.

D. You forgot to commit changes on feature branch.

Solution

1. Step 1: Understand --ff-only error cause

   The --ff-only option fails if a fast-forward merge is not possible.

2. Step 2: Identify when fast-forward is impossible

   If main has new commits not in feature, Git cannot fast-forward main to feature, causing the error.

3. Final Answer:

   The main branch has new commits not in feature. -> Option A

4. Quick Check:

   Fast-forward fails if main has new commits [OK]

Hint: Fast-forward fails if main moved ahead since branching [OK]

Common Mistakes:

• Assuming feature must be behind main
• Thinking empty feature branch causes error
• Confusing uncommitted changes with merge errors

5. You have a main branch and a feature branch. Both have new commits since branching. You want to merge feature into main but keep history linear without merge commits. Which approach is best?

hard

A. Use git rebase main on feature, then fast-forward merge.

B. Use git merge --no-ff feature to force a merge commit.

C. Use git merge --ff-only feature and abort if not fast-forward.

D. Delete main and rename feature to main.

Solution

1. Step 1: Understand the problem with fast-forward

   Since both branches have new commits, a fast-forward merge is not possible directly.

2. Step 2: Use rebase to linearize history

   Rebasing feature onto main moves feature commits on top of main, enabling a fast-forward merge afterward.

3. Step 3: Perform fast-forward merge after rebase

   After rebase, merging feature into main will be a fast-forward, keeping history linear without merge commits.

4. Final Answer:

   Use git rebase main on feature, then fast-forward merge. -> Option A

5. Quick Check:

   Rebase then merge = linear history [OK]

Hint: Rebase feature on main to enable fast-forward merge [OK]

Common Mistakes:

• Trying --ff-only merge when not possible
• Forcing merge commit breaks linear history
• Deleting branches unnecessarily