Merge strategies overview in Git - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a merge strategy in Git?

A merge strategy is the method Git uses to combine changes from different branches into one. It decides how to integrate the histories and content.

intermediate

Explain the recursive merge strategy.

The recursive strategy is Git's default. It handles two-parent merges by creating a new merge commit that combines changes from both branches, resolving conflicts if needed.

intermediate

What does the ours merge strategy do?

The 'ours' strategy keeps the current branch's content and ignores changes from the other branch during a merge. It is useful to override changes.

advanced

Describe the octopus merge strategy.

The octopus strategy merges more than two branches at once. It works best when there are no conflicts and creates a single merge commit.

beginner

What is a fast-forward merge?

A fast-forward merge happens when the current branch has no new commits since branching. Git just moves the pointer forward without creating a merge commit.

Which merge strategy is the default in Git?

A recursive

B ours

C octopus

D fast-forward

The recursive strategy is the default merge method Git uses for two-parent merges.

What does a fast-forward merge do?

A Creates a new merge commit

B Moves the branch pointer forward without a merge commit

C Ignores changes from the other branch

D Merges multiple branches at once

Fast-forward merges move the branch pointer forward when no new commits exist on the current branch.

When is the octopus merge strategy used?

A To keep only the current branch's changes

B To merge two branches with conflicts

C To merge multiple branches at once without conflicts

D To rebase commits

Octopus merges multiple branches simultaneously and works best when there are no conflicts.

What happens with the 'ours' merge strategy?

A Keeps changes from the current branch only

B Creates a merge commit combining both branches

C Keeps changes from the other branch

D Deletes the current branch

'Ours' strategy keeps the current branch's content and ignores the other branch's changes.

Which merge strategy creates a new commit combining two branches?

A fast-forward

B octopus

C ours

D recursive

The recursive strategy creates a new merge commit combining changes from both branches.

Describe the main differences between fast-forward and recursive merge strategies in Git.

Think about whether a new commit is created or not.

Explain when and why you might use the 'ours' merge strategy.

Consider a situation where you want to discard incoming changes.

Practice

1. What does the --no-ff option do when merging branches in Git?

easy

A. It creates a merge commit even if a fast-forward merge is possible.

B. It squashes all commits into one before merging.

C. It deletes the source branch after merging.

D. It aborts the merge if conflicts are found.

Solution

1. Step 1: Understand fast-forward merges

   A fast-forward merge moves the branch pointer forward without creating a new commit if no divergent changes exist.

2. Step 2: Effect of --no-ff

   The --no-ff option forces Git to create a merge commit even if a fast-forward is possible, preserving branch history.

3. Final Answer:

   It creates a merge commit even if a fast-forward merge is possible. -> Option A

4. Quick Check:

   --no-ff keeps history with merge commit [OK]

Hint: Remember: --no-ff always makes a merge commit [OK]

Common Mistakes:

• Confusing --no-ff with --squash
• Thinking it deletes branches
• Assuming it aborts on conflicts

2. Which of the following is the correct syntax to perform a squash merge of branch feature into main?

easy

A. git merge --squash feature

B. git merge feature --no-ff

C. git merge --fast-forward feature

D. git merge --abort feature

Solution

1. Step 1: Identify squash merge syntax

   The --squash option is used with git merge to combine all commits from the source branch into one commit on the target branch.

2. Step 2: Check command correctness

   git merge --squash feature is the correct syntax to squash merge the feature branch into the current branch.

3. Final Answer:

   git merge --squash feature -> Option A

4. Quick Check:

   Squash merge syntax = git merge --squash [OK]

Hint: Use --squash right after git merge for squash merges [OK]

Common Mistakes:

• Placing --no-ff instead of --squash
• Using --abort which cancels merges
• Assuming --fast-forward is a valid option

3. Given the following commands run on branch main:

git merge feature

If feature has 3 commits and no conflicts, what will be the result in the commit history?

medium

A. A single new merge commit combining all changes from feature.

B. Merge aborted due to conflicts.

C. Three separate commits from feature added to main with no merge commit.

D. No new commits; main pointer moves forward (fast-forward).

Solution

1. Step 1: Understand default merge behavior

   By default, if the main branch has no new commits since branching, Git performs a fast-forward merge, moving the main pointer forward.

2. Step 2: Analyze the scenario

   Since feature has 3 commits and main has no new commits, Git will fast-forward main to feature's tip without creating a merge commit.

3. Final Answer:

   No new commits; main pointer moves forward (fast-forward). -> Option D

4. Quick Check:

   Default merge with no divergence = fast-forward [OK]

Hint: If no new commits on main, merge fast-forwards [OK]

Common Mistakes:

• Assuming a merge commit is always created
• Thinking commits are duplicated
• Confusing conflicts with no conflicts

4. You tried to merge branch feature into main using git merge feature, but Git reports conflicts. What is the best way to resolve this?

medium

A. Delete the feature branch and start over.

B. Run git merge --abort to cancel the merge and lose changes.

C. Manually edit conflicting files, then run git add and git commit.

D. Use git reset --hard to force merge.

Solution

1. Step 1: Understand merge conflicts

   Conflicts occur when Git cannot automatically combine changes. Manual intervention is needed to fix conflicting files.

2. Step 2: Resolve conflicts properly

   Edit the conflicting files to fix issues, then stage changes with git add and complete the merge with git commit.

3. Final Answer:

   Manually edit conflicting files, then run git add and git commit. -> Option C

4. Quick Check:

   Resolve conflicts manually, then add and commit [OK]

Hint: Fix conflicts manually, then add and commit [OK]

Common Mistakes:

• Aborting merge loses progress
• Deleting branches unnecessarily
• Using reset which discards changes

5. You want to merge a long-lived feature branch into main but keep the commit history clean with a single commit representing all changes. Which merge strategy should you use and what is the correct sequence?

hard

A. Use git merge --no-ff feature to keep all commits and a merge commit.

B. Use git merge --squash feature then commit manually.

C. Use git rebase main feature then fast-forward merge.

D. Delete feature and copy files manually.

Solution

1. Step 1: Identify goal - single commit for all changes

   Squash merge combines all commits from the feature branch into one commit on main, keeping history clean.

2. Step 2: Correct merge sequence

   Run git merge --squash feature to prepare changes, then create a new commit manually with git commit.

3. Final Answer:

   Use git merge --squash feature then commit manually. -> Option B

4. Quick Check:

   Squash merge + manual commit = single clean commit [OK]

Hint: Squash merge then commit for one clean commit [OK]

Common Mistakes:

• Using --no-ff which keeps all commits
• Confusing rebase with squash merge
• Deleting branches instead of merging