Git - merge investigation

1. How to find out if branch has been merged into your current branch

2. How to find out if your current branch has been merged into any other branch

1. To check if a feature or branch has been merged into your current branch, use the git branch --merged command, the git merge-base command, or inspect the git log. 

Methods to Verify a Merge:

1. Using git branch --merged 

This command lists all branches whose tips are reachable from your current branch's HEAD, meaning they are fully integrated. 

First, ensure you are on the branch where you expect the feature to be merged (e.g., main):

git checkout <current-branch-name>

Then, run the command to list all merged branches:

git branch --merged

If the feature branch name appears in the output list, it has been merged into your current branch. 

To see branches that have not been merged, you can use the --no-merged flag instead: 

git branch --no-merged

2. Using git merge-base

This method determines the common ancestor between two branches. If the common ancestor is the same as the feature branch's tip, then the feature branch is fully merged. 

Find the last commit hash of the feature branch:

git rev-parse <feature-branch-name>

Find the best common ancestor between your current branch and the feature branch:

git merge-base <current-branch-name> <feature-branch-name>

If the output of both commands is the same commit hash, the feature branch is merged. 

3. Using git log

You can visually inspect the commit history for the commits from the feature branch within your current branch's history. 

Switch to your current branch:

git checkout <current-branch-name>

Check the log for commits from the feature branch:

git log <feature-branch-name>

If the commits from the feature branch are visible in the log, they are part of the current branch's history. For a more visual representation, you can use:

git log --decorate --oneline --graph --all

This shows a graphical history, making it easier to spot the merge commit. 

4. Using a Git Hosting Service (GitHub, GitLab, etc.) 

Check the status of the pull request (PR) or merge request (MR) associated with the feature branch on your web-based Git platform (e.g., GitHub, GitLab). The status will typically indicate whether the PR/MR has been successfully merged.

2. To find out if your current branch has been merged into any other branch, you can use the git branch --contains command. This command lists all branches that contain a specific commit, which in this case will be the tip of your current branch. 

Command Line Method

Get the SHA1 hash of your current branch's tip commit:

git rev-parse HEAD

List all branches that contain that commit:

git branch --all --contains <SHA1_hash>

Replace <SHA1_hash> with the output from the previous command. 

A more direct, script-based approach to get a clean list of all local branches your current branch has been merged into is provided by the experts on Stack Overflow:

bash

for branch in $(git for-each-ref --format="%(refname:short)" refs/heads/); do

    if [ "${branch}" != "$(git rev-parse --abbrev-ref HEAD)" ]; then

        if git merge-base --is-ancestor HEAD "${branch}"; then

            echo "${branch}"

        fi

    fi

done

This script iterates through all local branches and uses git merge-base --is-ancestor to check if all commits in your current branch (HEAD) are included in the history of the other branch. 

Visual Method

You can also use a graphical tool like gitk which is bundled with Git: 

Run gitk --all from your repository's root directory. The visual history will show which branches contain the commits from your current branch. 

Alternative: Git Hosting Services 

If you are using a service like GitHub, GitLab, or Bitbucket, you can often check the status of your pull requests or merge requests directly in the web interface. They will typically indicate if a branch has been merged and into which target branch.