How does Git perform a fast-forward merge?

Git performs a fast-forward merge by following these steps:

1. Check for Divergence: Git first checks if the branch being merged (e.g., feature-branch) has any commits that are not present in the target branch (e.g., master). A fast-forward merge is only possible if there are no divergent commits.

2. Move the Pointer: If there are no divergent commits, Git simply moves the pointer of the target branch (e.g., master) forward to the latest commit of the branch being merged (e.g., feature-branch). This effectively updates the target branch to include all the commits from the source branch.

3. Update the Working Directory: The working directory is updated to reflect the new state of the target branch, which now includes the changes from the merged branch.

Example Command:

To perform a fast-forward merge, you would typically use the following command:

git checkout master
git merge feature-branch

If a fast-forward merge is possible, Git will execute it without creating a new merge commit, resulting in a linear commit history.

Visual Representation:

Before the merge:

A -- B -- C (feature-branch)
         \
          (master)

After the fast-forward merge:

A -- B -- C (master, feature-branch)

This process keeps the commit history clean and linear, making it easier to follow.