[derefr]

> It’s essentially an anonymous branch. ... Maybe you should have explicitly branched, but hey, we’re all human.

This is the real key here. Most don't really want git-merge(1) or git-rebase(1). They want git-go-back-and-extract-my-commits-into-a-topic-branch(1).

[erso]

If you have some commits:

    A-B-C-D-E-F-G

Where B is master and origin/master, and you decide you want to make C..G into a topic branch, topicA:

git branch topicA

    A-B-C-D-E-F-G (master)
    A-B-C-D-E-F-G (topicA)

git reset --hard B

    A-B (master)
    A-B-C-D-E-F-G (topicA)

git merge --no-ff topicA

    A-B-----------H (master)
       \         /
        C-D-E-F-G (topicA)

[EdiX]

    git checkout -b a-topic-branch
    git checkout master

then you reset master to the remote master, there is a command to do it but I do this kind of things with gitk.

[michaelmior]

    git checkout master
    git reset --hard origin/master

[graywh]

Assuming you're already on master, you can replace those 2 commands with a single one: git branch a-topic-branch