Example
A rebase switches the meaning of "ours" and "theirs":
git checkout topic
git rebase master # rebase topic branch on top of master branch
Whatever HEAD's pointing to is "ours"
The first thing a rebase does is resetting the HEAD to master; before cherry-picking commits from the old branch topic to a new one (every commit in the former topic branch will be rewritten and will be identified by a different hash).
With respect to terminologies used by merge tools (not to be confused with local ref or remote ref)
=> local is master ("ours"),
=> remote is topic ("theirs")
That means a merge/diff tool will present the upstream branch as local (master: the branch on top of which you are rebasing), and the working branch as remote (topic: the branch being rebased)
+-----------------------------------------+
| LOCAL:master | BASE | REMOTE:topic |
+-----------------------------------------+
| MERGED |
+-----------------------------------------+
Inversion illustrated
On a merge:
c--c--x--x--x(*) <- current branch topic ('*'=HEAD)
\
\
\--y--y--y <- other branch to merge
We don't change the current branch topic, so what we have is still what we were working on (and we merge from another branch)
c--c--x--x--x---------o(*) MERGE, still on branch topic
\ ^ /
\ ours /
\ /
--y--y--y--/
^
theirs
On a rebase:
But on a rebase we switch sides because the first thing a rebase does is to checkout the upstream branch to replay the current commits on top of it!
c--c--x--x--x(*) <- current branch topic ('*'=HEAD)
\
\
\--y--y--y <- upstream branch
A git rebase upstream will first set HEAD to the upstream branch, hence the switch of 'ours' and 'theirs' compared to the previous "current" working branch.
c--c--x--x--x <- former "current" branch, new "theirs"
\
\
\--y--y--y(*) <- set HEAD to this commit, to replay x's on it
^ this will be the new "ours"
|
upstream
The rebase will then replay 'their' commits on the new 'our' topic branch:
c--c..x..x..x <- old "theirs" commits, now "ghosts", available through "reflogs"
\
\
\--y--y--y--x'--x'--x'(*) <- topic once all x's are replayed,
^ point branch topic to this commit
|
upstream branch
