Merge

This document explains the concept of fast forward and no fast forward merges in Git, as illustrated in the provided diagram.

Explanation

Initial State

Initially, we have two branches: master and dev.

graph TD;
    A[Task 1]:::task --> B[Task 2]:::task
    B --> C[Task 3]:::task
    C --> D[Final Task]:::finalTask
    C --> master[Master Branch]:::branch
    D --> dev[Development Branch]:::branch
    classDef finalTask fill:#90ee90, stroke:#000, stroke-width:2px;
    classDef branch fill:#f08080, stroke:#000, stroke-width:2px;

    linkStyle 0 stroke:#2ca02c,stroke-width:2px
    linkStyle 1 stroke:#2ca02c,stroke-width:2px
    linkStyle 2 stroke:#2ca02c,stroke-width:2px
    linkStyle 3 stroke:#0000FF,stroke-width:2px
    linkStyle 4 stroke:#0000FF,stroke-width:2px

When the master branch is merged into the dev branch and there are no new commits in the master branch, we can perform a fast forward merge. This will move the master branch pointer to the latest commit in the dev branch.

graph TD;
    A[Task A]:::task --> B[Task B]:::task
    B --> C[Task C]:::task
    C --> D[Final Task]:::finalTask
    D --> dev[Development Branch]:::branch
    D --> master[Master Branch]:::branch

    classDef task fill:#add8e6, stroke:#000, stroke-width:2px;
    classDef finalTask fill:#90ee90, stroke:#000, stroke-width:2px;
    classDef branch fill:#f08080, stroke:#000, stroke-width:2px;

    linkStyle 0 stroke:#2ca02c,stroke-width:2px
    linkStyle 1 stroke:#2ca02c,stroke-width:2px
    linkStyle 2 stroke:#2ca02c,stroke-width:2px
    linkStyle 3 stroke:#0000FF,stroke-width:2px
    linkStyle 4 stroke:#0000FF,stroke-width:2px

No Fast Forward Merge

If there are new commits in the master branch, a merge commit is created to combine the histories of the master and dev branches. This results in a no fast forward merge.

graph TD;
    A[Task A]:::task --> B[Task B]:::task
    B --> C[Task C]:::task
    C --> M[Merge Commit]:::merge
    C --> D[Final Task]:::finalTask
    M --> master[Master Branch]:::branch
    D --> dev[Development Branch]:::branch
    M --> D;

    classDef task fill:#add8e6, stroke:#000, stroke-width:2px;
    classDef finalTask fill:#90ee90, stroke:#000, stroke-width:2px;
    classDef merge fill:#ffcc00, stroke:#000, stroke-width:2px;
    classDef branch fill:#ff7f50, stroke:#000, stroke-width:2px;

    linkStyle 0 stroke:#2ca02c,stroke-width:2px
    linkStyle 1 stroke:#2ca02c,stroke-width:2px
    linkStyle 2 stroke:#ff4500,stroke-width:2px
    linkStyle 3 stroke:#2ca02c,stroke-width:2px
    linkStyle 4 stroke:#0000ff,stroke-width:2px
    linkStyle 5 stroke:#0000ff,stroke-width:2px

Commands

To perform a fast forward merge:

# Switch to master branch
git checkout master

# Merge dev branch into master
git merge dev

Optionally, you may choose to delete the feature branch after merging:

git branch -d dev               # Delete the local `develop` branch
git push origin --delete dev    # Delete the remote `develop` branch

To ensure no fast forward merge:

# Switch to master branch
git checkout master

# Merge dev branch into master with no fast forward option
git merge --no-ff dev

Summary

Fast Forward Merge: Moves the branch pointer forward without creating a new commit.
No Fast Forward Merge: Combines branch histories and creates a new merge commit.

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