To get a commit history that makes sense. It’s not supposed to document in what order you did the work, but why and how a change was made. when I’m knee deep in some rewrite and realize I should have changed something else first, I can just go do that change, then come back and rebase.
And in the feature branches/merge requests, I don’t merge, only rebase. Rebasing should be the default workflow. Merging adds so many problems for no good reason.
There are use cases for merging, but not as the normal workflow.
That is just not true. Merging is so much less work and the branch history clearly indicates when merging has happened.
With rebasing, there could be a million times the branch was rebased and you would have no idea when and where something got broken by hasty conflict resolution.
When conflicts happen, rebasing is equivalent to merging, just at the commit level instead of at branch level, so in the worst case, developers are met with conflict after conflict, which ends up being a confusing mental burden on less experienced devs and certainly a ”trust the process” kind of workflow for experienced ones as well.
The master branch never gets merged, so it is linear. Finding a bug is very simple with bisect. All commits are atomic, so the failing commit clearly shows the bug.
If you want to keep track of what commits belongs to a certain pr, you can still have an empty merge commit at the end of the rebase. Gitlab will add that for you automatically.
The ”hasty conflict resolution ” makes a broken merge waaaay harder to fix than a broken rebase.
And rebasing makes you take care of each conflict one commit at a time, which makes it order by magnitudes easier to get them right, compared to trying to resolve them all in a single merge commit.
No. There is a conflict during a rebase, you resolve it, and then it’s like there never was a conflict.
Even if you do it properly, the workflow is erasing history of that conflict existing and needing to be resolved. It leaves no trace of what has been worked on, when, and by whom.
Meanwhile, in another branch B created off main, someone else commits changes to the same part of the same file.
That other branch B gets merged to main.
Now, rebase branch A onto main.
The rebase stops at the commit 1 due to a conflict between main and branch A.
Fix the conflict and commit. This erases commit 1 and creates new commit 1' where the conflict has never existed. History has been rewritten.
Rebase successfully completes, branch A now contains different commits than previously, so it will need to be force-pushed to remote if it already exists there. The protocol has resistance against changing history.
Merge branch A to main.
No commit in main now contains any information that there was a conflict that was fixed.
Had a pull request workflow been used, the ”merge main to A” merge commit message would detail which files were conflicting. No such commit is made when using a rebase workflow, chasing those clean fast-forward merges.
I’m sure you’re here to educate me, but this is not about criss-cross merges between two different work branches, this is about whether it’s better to rebase a work branch onto the main branch, or to pull the changes from the main branch to the work branch.
I have an early draft of a blog post about them :) as a source control expert who built both these systems and tooling on top of them for many years, I think they're the biggest and most fundamental reason rebases/linear history are better than merges.
> whether it’s better to rebase a work branch onto the main branch, or to pull the changes from the main branch to the work branch.
The problem with this is that the latter has an infinitely higher chance of resulting in criss-cross merges than the former (which is 0).
It's definitely not 0 because rebase heavy workflows involve the rerere cache which is a minefield of per-repo hidden merge changes. You get the results of "criss-cross merges" as "ghosts" you can't easily debug because there aren't good UI tools for the rerere cache. About the best you can do is declare rerere cache bankruptcy and make sure every repo clears their rerere cache.
I know that worst case isn't all that common or everyone would be scared of rebases, but I've seen it enough that I have a healthy disrespect of rebase heavy workflows and try to avoid them when given the option/in charge of choosing the tools/workflows/processes.
To be honest I've used rebase-heavy workflows for 15 years and never used rerere, so I can't comment on that (been a happy Jujutsu user for a few years — I've always wondered what the constituency for rerere is, and I'm curious if you could tell me!) I definitely agree in general that whenever you have a cache, you have to think about cache invalidation.
rerere is used automatically by git to cache certain merge conflict fixes encountered during a rebase so that you don't have to reapply them more than once rebasing the same branch later. In general, when it works, which is most of the time, it's part of what keeps rebases feeling easy and lightweight despite capturing in the final commit output sometimes a fraction of the data of a real merge commit. The rerere cache is in some respects a hidden collection of the rest of a merge commit.
In git, the merge (and merge commit) is the primitive and rebase a higher level operation on top of them with a complex but not generally well understood cache with only a few CLI commands and just about no UI support anywhere.
Like I said, because the rerere cache is so out-of-sight/out-of-mind that's why problems with it become weird and hard to debug. The situations I've seen that have been truly rebase-heavy workflows with multiple "git flow" long-running branches and even sometimes cherry picking between them. (Generally the same sorts of things that create "criss-cross merge scenarios".) Rebased commits start to bring in regressions from other branches. Rebased commits start to break builds randomly. If what is getting rebased is a long-running branch you probably don't have eyes on every commit, so finding where these hidden merge regressions happen becomes full branch bisects, you can't just focus on merge commits because you don't have them anymore, every commit is a candidate for a bad merge in a rebased branch.
Personally, I'd rather have real merge commits where you can trace both parents and the code not from either parent (conflict fixes), and you don't have to worry about ghosts of bad merges showing up in any random commit. Even the worst "criss-cross merge" commits are obvious in a commit log and I've seen have had enough data to surgically fix, often nearly as soon as they happen. rerere cache problems are things that can go unnoticed for weeks to everyone's confusion and potentially a lot of hidden harm. You can't easily see both parents of the merges involved. You might even have multiple repos with competing rerere caches alternating damage.
But also yes rerere cache problems are so generally infrequent that it might also take weeks of research, when it does happen, just to figure out what the rerere cache is for, that it might be the cause of some of your "merge ghosts" haunting your codebase, and how to clean it.
Obviously by the point where you are rebasing git flow-style long runnning branches and using frequent cherry picks you're in a rebase heavy workflow that is painful for other reasons and maybe that's an even heavier step beyond "rebase heavy" to some, but because the rerere cache is involved to some degree in every rebase once you stop trusting the rerere cache it can be hard to trust any rebase heavy workflow again. Like I said, personally I like the integration history/logs/investigatable diffs that real merge commits provide and prefer tools like `--first-parent` when I need "linear history" views/bisects.
You have to turn rerere on, though, right? I've never done that. I've also never worked with long-running branches — tend to strongly prefer integrating into main and using feature flags if necessary. Jujutsu doesn't have anything like rerere as far as I know.
Hmm, yeah looks like it is default off. Probably some git flow automation tool or other sort of bad corporate/consultant disseminated default config at a past job left the impression that it was default on. It's the solution to a lot of papercuts working with long-running branches as well as the source of new problems as stated above; problems that are visible with merge commits but hidden in rebases.
And in the feature branches/merge requests, I don’t merge, only rebase. Rebasing should be the default workflow. Merging adds so many problems for no good reason.
There are use cases for merging, but not as the normal workflow.