新分支从复制的分支获取所有先前的提交

Question

if I create a new branch all the commits from the copied branch are coppied to the new one.

How can I stop this? I would like to have just new commits in the new branch..

Answer 1

Commits in git contain a reference on their parent commit. This is how git builds the history of your repository.

A branch on the other hand just points to a specific commit. It is literally a file which contains the SHA-1 key of the current commit. You can find them in the .git/refs/heads folder in your repository.

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When you create a new branch without specifying a commit the branch will point to the same commit HEAD currently points at. (Note that HEAD doesn't directly point at a commit but at a branch, but that's a different story.)

Let's assume you are currently on your development branch and want to create a new branch to work on a new feature.

git checkout -b new-branch

Now both development and new-branch will point at the same commit, lets say the key is DEF456 . This commit contains a reference to it's parent commit - as every commit does - which is ABC123 which in turn again contains a reference on it's parent commit and so on.

You see, git doesn't copy the history of a branch when creating a new branch, it just points to the same commit as the current branch does.

If you want to learn more about how git stores it's information internally you can take a look at the Git Objects chapter of the gitpro book .

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And as you already found in this question . You can force a merge commit, rather than a fast-forward, by using git merge --no-ff <branch-to-merge> .

A merge commit is special in the sense that it doesn't contain one refence on a parent commit, as most commits in git do, but it contains multiple references to it's parent commits. This defines a merge.

Answer 2

It sounds like you were really asking about forcing "real" merges rather than "fast forward" merges, and about "squash" merges (which are not actual merges at all). For completeness, though, I want to mention that there's one more thing you can do when creating a new branch-name:

git checkout --orphan -b newbr

In this case, git puts you on newbr without actually creating newbr yet. This means that the next commit will start a new, independent commit-graph within your repository. In other words, you will have multiple "root commits" in a single repository (a root commit is a commit that has no parents, vs ordinary commits that have one parent and merge commits that have two or more parents).

Multiple independent commit graphs within a repository are unusual, but supported: git's own source repository contains them, for instance. (The git program is maintained using git.)