What does it mean to git rebase a branch on top of incoming changes?
tl;dr A fundamental misunderstanding of the rebase operation.
I confused myself yesterday and I've not quite recovered. Rider's phraseology isn't helping me either, but maybe that's just me. When Rider offers to "Rebase the current branch on top of incoming changes, what does "on top" mean? I checked with two branches that were too similar to see the difference without making a change in one, and I am hesitant to make any changes anyway in case the rebase is different to branch and doesn't leave me with a nice, atomic "rebase commit" like a merge does.
I visualise commit "trails" as vertical lines starting with the first commit at the bottom. First I imagined the proposed rebase to be like a merge, with two parallel commit trails, both starting at bottom and being joined by a zip. But that's an actual merge not a rebase, my first mistake. The "on top" phrase made me think of the commit trails as horizontal lines, with the incoming changes being the top line, to be "zipped" onto the bottom line, my second mistake because that's still really a merge.
Now I think what Rider actually means by "on top" is like what I've read about rebase in some docs, where the local branch is a single vertical line starting at the bottom. Then the rebase will take incoming commits and place them in the same line as the local branch, at the bottom, pushing the newer local branch commits up to be on top of the incoming commits, thus remaking the base of the local branch, hence the term rebase.
But then the order of the commits in the local branch doesn't add up because some incoming ones would have originally been made after some local ones. To keep them in order git would have to insert incoming commits in the correct order between local commits, but isn't that just a merge?
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Rebasing something "on top of" something else does not make any sense in my mind at all
Something can be "based on" something else
But not "based on top of" something else
On top of is Rider's exact term
That much i understood
In my mind, rebasing means you basically re-write your branch to pretend it's been "based on" another commit entirely the whole time
Rebasing "on top of" is like having a multi layer cake.
If I have 3 green layers (branch I was based on's commits) and 3 red layers of cake (my new commits) then rebasing my cake would mean the branch I was based on has had additional commits since I took a copy. So I will take off my red layers, add on the new green layers and plop my red layers back on, I have changed the base of my cake to have more green layers than before, I have "rebased" my red layers
That's my understanding of rebasing yeah
The "on top of" still doesn't make sense in my mind
"rebase on" is enough imo
I am "rebasing" my cake to be "on top of" the new incoming commits
No yeah i get it
I just hate it
The fun begins when you have conflicts :3
With rebase --skip and rebase --continue
mmmm
With regards to commits after the ones you've made.... I dunno, I don't think it cares if theres no merge conflict, I have never really thought about it personally, it just works. Create a git repo, test and come back to us!
I've done this and I've had huge headaches
I had 3 PRs which were basically all based on one another
On 3 separate branches, which i created off of the previous (after making the PR)
But then changes were requested on the first PR and the fun began
Rebased
Seem they aren't in order of time anymore
And heres after a merge
Hope that was useful @Doktor9, I'll be deleting those in a mo because obvious name reasons
so, it doesn't take commits from your local branch
what a rebase does, in essence, is re-do every commit
so if master gets a new commit
and you rebase your feature branch "on top of" master
rebase gets rid of every commit you've made
pulls the commit from master
then re-does what happened in every commit, in order, but now with that new commit from master at the start
What i meant to say with this
you could do this yourself if you wanted
Thanks, I think half my confusion here started with the fact that both my branches are
master and origin/masterah, yeah
that's never fun
always really hard to tell what's from where
Then it's not really a rebase right? Or it shouldn't be at least?
Exactly
Just a normal pull should do it here
no, you can rebase a local branch onto a remote one
if you have local commits on your branch, and the remote master got different new commits in the meantime
Sounds weird
Yes! That'
it basically deletes your local copy and starts from scratch
Yeah I'd just pull for this. Never even considered rebasing
with whatever is on your new master
That's what is making me pause, is commits to origin made before commits to local
that would make a merge commit
Hm
which you might not want
you don't actually have to use the rebase command for this though
Just squash i guess lol
you can do
git pull --rebase
although I'd be careful with it
especially if there would be conflictsAha, OK, I see a straight pull is missing from the git toolbar in Rider, leaving me a "Fetch" which is where I must decide if I want a rebase or a merge commit
the default for just pull with no flags is to make a merge commit
iirc
Makes sense
It's not just "Pull", it's explicitly a different operation called "Fetch"
In Rider that is not in git
fetch just asks the remotes for what has changed
I think Rider then sees there are changes and wants to know how to apply them, rebase or merge
Unknown User•2y ago
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I think I have mine set to fast-forward only
"Pull is just a fetch and merge" - Ooh, more rays of light in the darkness, thanks
fast-forward is basically "there are no actual changes here compared to what we're pulling, we can just grab the new commits and add them to the branch without any fuss"
if that fails, my git yells at me and tells me I should pick what to do :p
you know, I wonder if any universities have classes dedicated to just learning source control
I still don't quite get it, but now I have time to make a test project myself, but thanks a lot, you can remove your images
I must finish my PluralSight git course, it's varsity level, but we're still exploring the content of object files in the .git folder
I have no idea what git is actually doing to store these commits lmao
It's not as opaque as it might seem, all a bunch of lists (files) of hashes, just like your history
git cat-file -p HEAD, and work from there. Use that to print the contents of any hashes you find, and keep diggingI think my takeaway here is that rebase may well result in the commits not being in order?
Unknown User•2y ago
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Ish. Rebase takes a set of commits, and rewrites them to sit on top of another commit that you specify. So the order of the set of commits that you're rebasing won't change, but they will be sat on top of a new parent
Remember that git's commit history is a graph anyway, so there isn't a single total order across all branches to start with
... and it you're doing any of these operations without visualising what they're doing to the graph of commits, then stop, open a history viewer like
gitk --all, and make sure you're comfortable with how things look now, and what you want them to look like after you've finished
Interactive rebase, with commit --fixup / --squash, is one of my favourite thingsI think more than half my problem is trying to visualise a single history behind the graph representing it, i.e. eventually, somehow, commits from all branches on the graph appear to be in some order
There's no notion of that though. This isn't SVN
Your history really is a gragh, with no total order
My very first VCS, maybe that's why lol
I lie, my first was SourceSafe
You poor thing
History is a singly-linked list, where each commit has a single parent (merge commits have 2+ parents), and multiple commits can share the same parent
Anyway, your course should get onto that. Other good resources:
* https://git-scm.com/book
* https://jwiegley.github.io/git-from-the-bottom-up/
* http://pcottle.github.io/learnGitBranching/
That last one is particularly good if you're struggling to visualise things, as it's all about the visualisation
Thanks man, I think I've tried that last one before, looks very familiar, but I didn't give it enough time, or didn't properly follow the lessons. I know I gave up quickly