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Take the following case:
I have some work in a topic branch and now I'm ready to merge back to master:
* eb3b733 3 [master] [origin/master]
| * b62cae6 2 [topic]
|/
* 38abeae 1
I perform the merge from master, resolve the conflicts and now I have:
* 8101fe3 Merge branch 'topic' [master]
|\
| * b62cae6 2 [topic]
* | eb3b733 3 [origin/master]
|/
* 38abeae 1
Now, the merge took me some time, so I do another fetch and notice that the remote master branch has new changes:
* 8101fe3 Merge branch 'topic' [master]
|\
| * b62cae6 2 [topic]
| | * e7affba 4 [origin/master]
| |/
|/|
* | eb3b733 3
|/
* 38abeae 1
If I try git rebase origin/master from master, I'm forced to resolve all conflicts again, and I also lose the merge commit:
* d4de423 2 [master]
* e7affba 4 [origin/master]
* eb3b733 3
| * b62cae6 2 [topic]
|/
* 38abeae 1
Is there a clean way to rebase the merge commit so I end up with a history like the one I show below?
* 51984c7 Merge branch 'topic' [master]
|\
| * b62cae6 2 [topic]
* | e7affba 4 [origin/master]
* | eb3b733 3
|/
* 38abeae 1
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The rebase operation itself combines resets, labels, merges to preserve the same structure. The tool itself rewinds before each merge tree, picks commits, then creates a merge commit. The very same steps can be done manually to achieve the same result.
By default, the git pull command performs a merge, but you can force it to integrate the remote branch with a rebase by passing it the --rebase option.
As with a normal git rebase, git with --preserve-merges first identifies a list of commits made in one part of the commit graph, and then replays those commits on top of another part. The differences with --preserve-merges concern which commits are selected for replay and how that replaying works for merge commits.
Reading the official Git manual it states that “rebase reapplies commits on top of another base branch”, whereas “merge joins two or more development histories together”. In other words, the key difference between merge and rebase is that while merge preserves history as it happened, rebase rewrites it.
There are two options here.
One is to do an interactive rebase and edit the merge commit, redo the merge manually and continue the rebase.
Another is to use the --rebase-merges option on git rebase, which is described as follows from the manual:
By default, a rebase will simply drop merge commits from the todo list, and put the rebased commits into a single, linear branch. With --rebase-merges, the rebase will instead try to preserve the branching structure within the commits that are to be rebased, by recreating the merge commits. Any resolved merge conflicts or manual amendments in these merge commits will have to be resolved/re-applied manually."
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