Merging is a fundamental concept in Git that allows you to combine changes from different branches into a single branch. This is particularly useful in collaborative environments where multiple developers work on different features or fixes simultaneously. In this section, we will cover the following:

1. Understanding Merging
2. Types of Merges
3. Performing a Merge
4. Practical Example
5. Common Merge Issues and Solutions
6. Exercises

Merging in Git is the process of integrating changes from one branch into another. Typically, you merge a feature branch into the main branch (often main or master) once the feature is complete and tested.

• Source Branch: The branch whose changes you want to integrate.
• Target Branch: The branch into which you want to integrate changes.

There are two primary types of merges in Git:

1. Fast-Forward Merge: This occurs when the target branch has not diverged from the source branch. Git simply moves the target branch pointer forward to the latest commit in the source branch.
2. Three-Way Merge: This occurs when the target branch has diverged from the source branch. Git creates a new commit that combines the changes from both branches.

• Scenario: The target branch has no new commits since the source branch was created.
• Result: The target branch pointer is moved forward to the latest commit in the source branch.

• Scenario: Both the target and source branches have new commits.
• Result: A new merge commit is created that combines the changes from both branches.

1. Switch to the Target Branch:

   git checkout main
   

2. Merge the Source Branch into the Target Branch:

   git merge feature-branch
   

3. Resolve Conflicts (if any): If there are conflicts, Git will pause the merge process and allow you to resolve them manually. After resolving conflicts, you need to add the resolved files and complete the merge:

   git add resolved-file.txt
   git commit
   

Let's walk through a practical example of merging a feature branch into the main branch.

• Main Branch: main
• Feature Branch: feature-login

1. Create and Switch to the Feature Branch:

   git checkout -b feature-login
   

2. Make Changes and Commit in the Feature Branch:

   echo "Login feature code" > login.txt
   git add login.txt
   git commit -m "Add login feature"
   

3. Switch Back to the Main Branch:

   git checkout main
   

4. Merge the Feature Branch into the Main Branch:

   git merge feature-login
   

5. Verify the Merge:

   git log --oneline
   

• Issue: Conflicts occur when changes in the source and target branches overlap.
• Solution: Manually resolve conflicts in the affected files, then add and commit the resolved files.

• Issue: Git refuses to merge branches with unrelated histories.
• Solution: Use the --allow-unrelated-histories flag to force the merge.

  git merge feature-branch --allow-unrelated-histories
  

1. Create a new branch called feature-1.
2. Make a change in feature-1 and commit it.
3. Switch back to the main branch and merge feature-1 into main.

1. Create two branches, feature-2 and feature-3, from main.
2. Make conflicting changes in both branches and commit them.
3. Merge feature-2 into main.
4. Attempt to merge feature-3 into main and resolve the conflict.

Solution 1: Basic Merge

Solution 2: Merge Conflict Resolution

Merging branches is a crucial skill in Git, enabling you to integrate changes from different branches and collaborate effectively with other developers. Understanding the types of merges and how to resolve conflicts will help you maintain a clean and functional codebase. In the next section, we will delve into resolving merge conflicts in more detail.