如何合并git分支以使主题提交成为孤立的？

Question

I'm still coming up to speed with some of the more advanced features of Git...

Given the following history, how can I clean up topic branch merges so they appear in history as a single commit?

[master] - - - - - - - C - - -
   \
   [feature] - A - - B - - D -

Ideally, I'd like to rebase [feature] with [master] at D and then merge [feature] into [master], leaving A and B orphaned.

I thought I could do this simply by:

$ git rebase master # on feature branch
$ git co master
$ git merge --no-ff feature

and then clean up the orphaned commits with

$ git gc --prune=now --aggressive

That still leaves A and B in the history though - Am I missing something?

Answer 1

If I redraw your diagrams to place the branch markers at the tip of the branch (which reflects the actual representation of branches) your original situation is:

o --- C (master)
 \
   --- A --- B --- D (feature)

And after rebasing and merging with --no-ff as you describe, you now have:

o --- C ------------------ M (master)
 \      \                 /
  \       A' --- B' --- D' (feature)
   \
    --- A --- B --- D

As I understand it, you now want to make sure that A , B and D disappear from your repository. Firstly, I would say that I strongly recommend that you don't worry about these commits.

However, if you really want to get rid of them, then you will have to make sure that they are truly unreachable, or git gc --prune=now --aggressive will not remove them. As it is, they will still be pointed to (at least) by the reflog for feature . There are various ways of expiring entries from the reflog, eg with:

git reflog expire --expire=now feature

... or a safer option should be to set the config variable gc.reflogexpireunreachable to now and expire the reflog:

git config gc.reflogexpireunreachable
git reflog expire feature

In either case, you would then need to run git gc --prune=now --aggressive afterwards again.

However, to reiterate what I said above, I wouldn't do this - those commits aren't hurting anyone and the reflog is a valuable safety net when using git.

Answer 2

If you want to "fuse" A, B and D, you can use an interactive rebase.

If your branch feature is on top of master (which it will be after you have issued git rebase master on this branch), do:

git rebase -i master

Then, in the file which will open in an editor, replace the pick on commits A and B with squash . Git will then squash A and B into D, and an editor will pop with the commit messages for all squashed commits.

Answer 3

If you want to collapse the effect of a branch into a single commit, then from master do:

git merge --squash feature
git commit

although IMHO being able to keep the individual commits on the branch intact is actually a good feature most of the time.

Alternatively, you could use git rebase -i on the branch and tell it to squash all the commits together, and then merge the squashed result onto master.

Answer 4

Why would it remove A and B?

The git rebase master will make feature to be branched off the tip of master and when you commit, all the commits from feature will come to master. Thus you will see A and B ( actually A' and B')

And git gc doesn't have anything to do with what you see in the history. It removes dangling commits ( which can be A and B, but you have A' and B' in master now)

If you want them to come as single commit, try the --no-commit option or look at other alternatives like git rebase -i ( and squash)