检查一个分支是否已经合并到 master

git branch --merged master lists branches merged into master

git branch --merged lists branches merged into HEAD (i.e. tip of current branch)

git branch --no-merged lists branches that have not been merged

ref: https://stackoverflow.com/questions/226976/how-can-i-know-in-git-if-a-branch-has-been-already-merged-into-master