[datascienced]

I wont claim to understand C and the reason why <> is better than “”. I assume it is.

But the fact that a merge can have arbitrary changes in it always bothers me!

This is a case for rebase over merge if there are conflicts.

You could have a merge of 2 empty repo parents where the result is the complete source of the latest version of Kubernetes!

[Groxx]

Yep. Stuff like this is part of why I'm a rebaser.

Rebase is simple. Always. The end result is obvious and clear and can only be interpreted in one way.

Merge has lots of little sharp edges and surprises if you don't know every single tiniest detail.

Almost nobody knows it in that level of detail, so it's a terrible choice for interacting with anyone else. If you're on your own, sure, do whatever - many things are not built solo though.

[noirscape]

My personal preference is merge but using the --no-ff flag. That way you get all the advantages of a rebase (since all your original commits are rebased into the target branch) but you also get a merge commit to confirm that all those changes were a part of the same set of patches.

That can often help a lot to figure out why something ended up the way it did, but you also don't turn your entire history into a flat pile of disparate commits.

[Groxx]

Yeah, I do kinda like this setup too. You can have both readable (rewritten) history and structured sub-commits for "a change" rather than a totally flat stack. Plus I don't care about your local history, but I do care about the final history.

It's definitely how I prefer to review code (big changes broken up to isolated portions that are easier to validate, and the whole thing at once so you don't get lost in the trees), so it's how I would prefer to read it later too.

It does still have merge commits where stuff can hide though :/ and you've got to remember --first-parent :/ and all not-merge-focused things so have problems with it :/

[zilti]

"But it is littering the commit history with useless commits!" is what I always hear

[skywal_l]

And the best answer is: "Why do you do useless commits?".

With `git amend` and `git fixup` you can arrange your commits to be clean, properly documented and self explanatory (and maybe atomic but that's a little harder). It takes a little time but it is hugely beneficial to code reviews and bug investigation.

[wdfx]

Some people however see using features like amend, squash, and force push as potentially destructive actions in the hands of a novice, which can lead to loss of not only the author's work but also other people's. Using merge almost never results in any sort of loss and is easier to work with for those who still don't quite understand the risks.

[skywal_l]

You are associating the use of `amend` and `fixup` with force push. It's perfectly fine to rework your commit history locally and even force push to your own local branch. It should never be possible (except to people administrating your repo) to force-push to any public or even shared branch.

Nobody should be able to force-push to master (or any public branch) except on specific occasion. In that case, someone is authorized, performs their specific action and then get de-authorized.

This is pretty basic.

[pjc50]

"Force push" is something that should be restricted to a very few senior people anyway; once you do that, you can't rewrite shared history any more and a lot of the worries go away.

[vundercind]

This is a great way to get me to clutter the shared repo with throwaway branches that I’ll later replace (deleting the old one—if you let me).

[Izkata]

Meanwhile the biggest issues I actually see in novices are when their IDE presents them with buttons that don't coincide with a single version control action (can you guess what "sync repo" will do?) and using those puts their checkout into a weird state.

Usually when using the commands directly they're more careful, but have the mindset "an IDE wouldn't intentionally break something so this button must be safe to click".

[Groxx]

Custom terms on top of git is a bafflingly bad decision.

IDEs in particular should expose the details all the time, and show the command that's being run, so it can teach people passively instead of misleading them and leaving them stuck when it breaks.

[roodrax]

totally agree here. commits are not for saving "your-current-work". Its about marking a definite step of change in the realm of the project itself.

making commits atomic is harder because we tend to just write code, without first breaking up the requirement into atomic pieces

[xorcist]

Commits are for saving your current work. Commit early, commit often. Just clean them up when you're done!

Don't push half-baked work on other people! You waste their compute cycles needlessly, from now until the end of time.

[CoastalCoder]

I sometimes wish git supported hierarchical commits.

I.e., git can retain two representations of a sequence of commits: the original sequence, and also a larger commit that (a) produces the exact same code change as the sequence, and (b) has its own commit message.

[pjc50]

Merge does that, yes, hence the preference for rebase flows.

(I'm surprised this got a downvote when that's how we got here: a situation in which a change was ""hidden"" in a merge commit that would have been explicit in a rebase workflow)

[btilly]

One idiot with rebase destroys history with no trace. I worked with such an idiot in a parallel team. I can't say how many weeks of work randomly got destroyed by said idiot.

I hate rebase on shared code I don't care how clean jt looks. Don't mess with history.

[doix]

I really don't understand how you can lose weeks of work. The person that would have done the force push would have the original commit in their reflog. ORIG_HEAD would be set.

Everyone else that had a copy of the repo would have had a copy of the "lost" commits.

I really cannot imagine how many things would have to go wrong for weeks of work to be lost.

[chaorace]

There is a hierarchy to these things:

- Person who destroys git history

- Person who hates destroying git history

- Person who knows how to recover "destroyed" history

- Person who knows how to truly destroy git history

[pvdoom]

> Person who knows how to truly destroy git history

The Gitsatz Haderach

[pcl]

> - Person who knows how to truly destroy git history

… tell me more!

[dale_glass]

A rebase can be undone, because the old commits keep hanging around in the repo. Rebase doesn't delete or rewrite anything, it just creates new commits and adjusts branch pointers, so the old stuff is still there just hard to get at because nothing points at it anymore.

You just need to find an old commit ID somewhere, normally the reflog.

The old stuff will go away on its own eventually due to git's self-maintenance procedures removing unreachable commits, or it can be done forcefully by adjusting the gc parameters to get rid of it.

[doix]

I cannot imagine how one could _truly_ destroy git history. You could destroy it locally, sure no problem. You _might_ be able to destroy it on your remote, but if you're using something like Github/Gitlab/Bitbucket I'm sure they'll have a cache that isn't trivial to remove from. But even if you remove it locally and from remote, there's no way you're removing it from other peoples clones. And other people could have pushed to other remotes.

Stuff "leaks" so much in git, that it's really hard to lose work. The only way I could see someone losing work is if they never commit or if they never push. But even if you don't push and just rebase, you're not losing work. You would have to go out of your way to delete git history locally.

[btilly]

What went wrong was multiple teams on unsynchronized 2 week schedules, and a culture that said that we had to accept the force push when other teams released.

So we released at the end of our cycle. It gets used for, if a vague memory serves, end of months billing. Meanwhile someone on another team "merged" our code, and actually randomly dropped a big chunk of our work. A week later they release. Some (but not all) of our features disappear. We pull that and don't notice because we're on a new sprint. Wait until the end of the month, users try to do billing. "Hey, why did you take away those features you built for us a month ago?" "What, we never...?"

We had no clue what happened.

This got to repeat a couple of times before we figured out what must be happening. We made changes to the release process so we could track what was actually released each time, with its history. We tracked down who we thought was making the mistake, but didn't have enough evidence to prove it to his manager. That didn't stop the idiot from making the mistake, but it did streamline the process of recovering it. Meaning we had the version with our feature, we had current code, and "just" had to sort out conflicts rather than rewrite from scratch.

Now that you've heard the story, can you see how weeks of work could be lost before we figured it out? And can you understand how we could have lost history?

This was a decade ago. At my next job we had more competent people. But there we had a huge debates between rebase and merge people. There are arguments on both sides. My conclusion was that about 90% of the time, rebase makes things simpler and easier. But that remaining 10% of the time makes the 90% not worth it.

Just learn how to merge properly.

[doix]

I'm pretty sure your code was still around at that point, by default git keeps stuff around for 90 days. Although to be fair I don't know if that's the case today nor if it was the case a decade ago.

What you're describing does sound awful, but I'm pretty sure that idiot could have found a way to mess up a merge. The entire workflow sounds completely fucked, I'm not convinced it's entirely fair to blame rebase in that case.

> Just learn how to merge properly.

I know how to merge and rebase properly. My favorite PR merge strategy is rebase + merge --no-ff. So your master branch is nice and linear, but you can still see where your PR merges came in. Let's you have a "all PRs get squashed" view of the world by just adding '--first-parent' to your git commands, but also lets you have the inner details for when you're git bisecting or spelunking trying to figure out why a certain line exists.

Most people hate what I describe though, similar to mixing spaces and tabs.

[btilly]

My code may have been around somewhere. I suspect I'd done gc, in which case it wasn't. But my git skills then were certainly not as good as they are now. (I'd only recently switched from svn at that point.)

I agree that the workflow was a mess in multiple ways. A lot of which were organizational decisions that I was in no position to influence.

Your favorite PR strategy is fine if you're doing it locally. However when it is done on master, you're going to have to get master again by force. Because changed history creates conflicts. Which means that you're going to have to hope that everyone only did it your way, and no idiot created conflicts in some other stupid way that you'll suffer for later.

I'd prefer to merge to head early. Merge to head often. Merge from head often. Don't have long-running shared branches. This does take some other forms of discipline though.

[doix]

I've never worked anywhere on master directly. Always in feature branches that then get merged to master (ideally with my strategy). So basically master always moves forward and it's history is never rewritten.

Master is always locked down anyway by "something" - no idea what the technical term for Github/Gitlab/Bitbucket is. Stopping people from force pushing to master prevents the sort of stuff that happened to you. Even if you don't have any "idiots", you really don't want a poor intern accidentally slightly pissing off everyone.

> I'd prefer to merge to head early. Merge to head often. Merge from head often. Don't have long-running shared branches. This does take some other forms of discipline though.

I agree with everything there, except I rebase instead of merge. So when I merge my branch to master, it's a nice neat little package that sits on top of master. It doesn't have the history of 10 merges I did while I was developing because I don't see the value in those merges.

But hey, to each their own. When I was younger, I used to get into heated debates about why I was right, now I don't really care. I'm either in a branch of my own and can do whatever I want, or working with someone and then I'll just copy whatever they do to not confuse them.

[arghwhat]

One never rebases shared code. They rebase their own work branch. Messing with history of master/main/integration branches should be blocked.

Rebase is a necessary part of a workflow even if you like merge commits. You're severely missing out if interactive rebases are not part of your toolbox.

[Feathercrown]

I wouldn't consider rebasing your own local commits on top of a more recent remote master to be messing with history in any meaningful way, and that's the most useful method of rebasing.

[quectophoton]

I can give an example scenario.

Assuming "H" is the hash of the current state of the repository content, consider this initial state of the repository (most recent first):

    H(3) Implement feature B
    H(2) Implement feature A
    H(1) Initial commit

Now you implement "shiny feature", so your history in your branch looks like this:

    H(5) Shiny feature, improvements.
    H(4) Shiny feature, initial implementation.
    H(3) Implement feature B
    H(2) Implement feature A
    H(1) Initial commit

You tested H(4) and H(5), and everything looks good.

Then you `git pull --rebase`, and your history looks like this:

    H(10) Shiny feature, improvements.
    H(9) Shiny feature, initial implementation.
    H(8) Pulled commit C
    H(7) Pulled commit B
    H(6) Pulled commit A
    H(3) Implement feature B
    H(2) Implement feature A
    H(1) Initial commit

You test H(10) because it's the current state of your repo, looks good, and merge (or create PR, whatever).

With the usual pull request flows, `H(9)` (i.e. anything between your new "base" and your most recent commit) usually stays untested, entirely ignored by the developers, and you would only ever find out if you ever need to bisect.

Not usually a problem, unless you have a rule of "every commit should be verified/tested" and the untested commits have a change that doesn't prevent a build but still causes issues (e.g. something that's only visual, or a new config file was added to a "conf.d" directory and its presence changed some behavior, stuff like that).

[citrin_ru]

To avoid this you can squash H(9) and H(10) before pushing to a shared branch, this way only one tested commit will be added on top of existing commits.

[lmm]

Rebasing unpushed commits is ok. But I have yet to see a workflow that provides good enough guardrails to make it something you can do safely.

[saagarjha]

Protect your main branch?

[lmm]

One of the great advantages of git is being able to pull from other people's feature branches, not just master. So protecting just master isn't good enough.

[saagarjha]

Yeah so you have them go through the workflow that doesn’t ruin things, like pull requests?

[from-nibly]

--force-with-lease

And only on working branches. I do this every single day.

[lmm]

Not good enough, that can mean you rebase changes that someone else has based further work on (but hasn't pushed it yet, or has pushed it to a different branch).

[from-nibly]

Why are you having people base their work off your in progress work? Git is not the issue with what you are describing.

[globular-toast]

Rebase cannot destroy "weeks of work". No git command can delete commits. Unless you have some insane garbage collection policy that is very far from any defaults. This is your fault for not understanding your tools.

[ansible]

Didn't you guys have filesystem backups of a shared git repository?

This is exactly what backups are for.

[nvy]

I believe that the semantics of < > vs "" is actually compiler-dependent but on every compiler that matters, #including with angle brackets is the semantic for "the system header" whereas using quotes gives preference to files in your local source tree.

So for example if you #include <foo> then the compiler (actually the preprocessor, but whatever) looks in the system's standard location, whereas if you #include "foo" then it looks in the local tree.

[ephimetheus]

I think that’s just the ordering though. “” will also end up searching the system paths, it will just check the local paths first.

[ripe]

You are right; a good explanation of the rules is in the C FAQ [1], which points to a newsgroup posting by Kaz Kylehu [2].

I am posting the summary here, although please do read the original if you have time:

The most portable thing to do is to use "" for including files within your project, and to use <> only for implementation supplied files.

(Disclosure: I was one of the contributors to the C FAQ).

[1] https://c-faq.com/cpp/inclkinds.html

[2] https://c-faq.com/cpp/inclk.kaz.html

[prerok]

What I find strange is that <> traditionally included system header files and "" included local files. They used different include paths, so you could have a header file in your sources with the same name as the system header file and then could control whether you are including one or the other based on using <> or "".

Anyway, I thought the distinction was lost in later compilers in favor of a single include path and then just taking the first file found when looking at potential matches through include path.

It seems the author of that merge thought the same thing. So, the distinction is actually still used by compilers?

[pavon]

With both GCC and Visual C++, the “” form first searches local paths and then system paths, while the <> form only searches system paths. Guess some BSDs are stricter about local paths.

[Gibbon1]

> But the fact that a merge can have arbitrary changes in it always bothers me!

After that xy thing where they were trying to install a back door having changes that are hidden like this is a big red flag.

In fact changing include <something.h> to include "something.h" with a hidden commit like this isn't a red flag it's a big rotating alarm with a siren. Someones trying set things up to include malicious code via a faked system lib.

[saagarjha]

Sadly, not all of us can live in the tech equivalent of Bond films. There is only so many xz backdoors to go around.

[hoseja]

There could be thousands of similar manchurian developers right now and it wouldn't even be a significant effort.

[saagarjha]

Until they're activated how are you going to know?

[arghwhat]

All but the first commit has parents. All commits point to the state of the file tree at that point.

A "merge commit" is nothing more than a commit claiming any number of parents greater than one. It is still its own file tree reference that decides how the tree looks, and nothing dictates that it should be related to the parents.

[tsimionescu]

If that were true, then git log -p would have worked. The reality is that merge commits are treated differently from other commits by many parts of git. Saying that they are "just a commit with multiple parents" gives people the wrong impression.

Git is more than the data structure backing it. And many parts of git make all sorts of assumptions that treat things that are more or less identical in the data model as actually being different. Tags are not the same thing as branches, for example, even though they are stored in virtually the same way.

[arghwhat]

Well, yes - git log does have special handling of commits with multiple parents because everything it shows is a special cased lie. Why? Because commits do not contain diffs or patches, but are instead full snapshots of the repository as a whole at a point in time.

git log -p is a convenience tool that tries to show code progression, and so it comes up with these simple diffs. Showing a graph of N-way conflict resolutions would not help the user trying to get an overview. Other tools exist to track the origin of a particular change, such as git blame.

It is important to understand what a git commit actually is exactly because of the caveats of such convenience interpretations. Otherwise you'd have no idea where a conflict resolution is stored, and you'll run into the surprises mentioned here.

In my opinion, git also becomes a lot easier to work with once you understand the low-level details, as you realize which high-level tools are similar, compatible, or fit or unfit for a a specific purpose.

[tsimionescu]

What git log shows is not "a lie", it is a part of its data model. Git is all of its commands, not just the low level details. Commits are both snapshots of the entire repo, and diffs, and delta compressions - none of these is "a lie".

[arghwhat]

> Commits are both snapshots of the entire repo, and diffs, and delta compressions - none of these is "a lie".

Commits are never diffs. Commits are snapshots, and sometimes git computes a diff between two commits. Commits are also never delta compressions, but can be stored within a delta-compressed packfile.

Whether you like it or not, git is primarily its low level details. The porcelain stacked on top changes, and differs depending on the user's client (e.g., a GUI using libgit2). However, that "git log -p" is "part of git" that git log -p is not trying to convince you that commits are diffs and show you a true chronicle. It instead assumes that you know what commits are, and that you are asking for an easy to read overview of what has been going on.

Accepting that commits are always solely snapshots will make the issues you run into when working with the porcelain easier to understand, especially when exposed to more than one client.

(Knowing about packfiles and delta compression can also be useful when looking into performance/resource utilization.)

[arghwhat]

*However, that "git log -p" is "part of git" does not change that git log -p is...

[kccqzy]

You are right that conceptually this is okay. But it is a UI problem that commands the author tried didn't manage to show the difference between the merge commit against any of its parents.

[robin_reala]

Technically you can have multiple first-commits in a Git repository. For example, Linux had 4 initial commits in 2017: https://www.destroyallsoftware.com/blog/2017/the-biggest-and...

[arghwhat]

Indeed, through commits with multiple parents (merges), you can end up having multiple orphan commits (initial commits).

Multiple initial commits are a bit rarer, usually stemming from merging in entirely different git repos with their own separate history as part of consolidation.

[devjab]

Wouldn’t you have the same amount of merge conflicts with rebase? Especially if you don’t do it often, which you frankly also should with merge?

I have to admit that I never really understood the advantages of rebase, and what I mean by this is they I actually don’t understand how the dangers of rebase out-weighs any form of advantages. Especially because on of the major advantages of merge is that you can squash your local commit history when you submit it to your main branch.

What we do is that we tie every pull request to a relatively small feature task, and because we do this, we genuinely don’t care about the individual commits developers do. Which means they can commit really silly messages if they are heading to a meeting or if they are just tired at the end of the day. It also helps with them merging main into their branch often, because it doesn’t taint the history.

The biggest advantage we’ve seen, that maybe we didn’t expect, is that nobody ever fucks up our tree in a way that needs someone who actually understands git to solve. We’ve also locked down the use of force push so that is not available to anyone unless it’s absolutely needed. Part of the reason I set this up initially was to protect myself from me, but it’s been a good thing since.

But I’m actually curious if it’s wrong.

[doix]

> Especially because on of the major advantages of merge is that you can squash your local commit history when you submit it to your main branch.

Squashing is in no-way limited to merging and is actually done by doing an interactive rebase. Nothing is stopping you from squashing without creating a merge commit. It's entirely separate.

If you're squashing everything anyway, what does merging even give you? Is your main branch just:

* merge B

* squashed commit B

* merge A

* squashed commit A

If you didn't merge, you'd have:

* squashed commit B

* squashed commit A

> What we do is that we tie every pull request to a relatively small feature task, and because we do this, we genuinely don’t care about the individual commits developers do.

Except eventually there is a large feature task and then you end up with a giant commit that is annoying when git-bisecting.

But at the end of the day, these things only matter if you are spelunking through git history and/or using things like git bisect. If your git history is "write-only & rollback", then none of this stuff matters.

[xorcist]

> advantages of merge is that you can squash your local commit history

No, it's the other way around. Squashing is a type of rebase.

Most workflows involve both. Merges can also be fast-forward merges, which are indistinguishable from rebases. Choosing between a rebase and a merge operation is often the wrong question to ask. The question is what state you wish the repository to end up in.

> I’m actually curious if it’s wrong

Look at "git log". It is readable and easy to understand? It is obvious why each commit was made, and why alternative solutions were turned down?

Are you able to use "git bisect" to track down problems?

Then you're doing it right. If not, think about what a functional commit log would look like and how you would get there. Working together is culture, and what type of merges you decide to use is just a tiny part of that culture.

[paulddraper]

But a rebased commit can also have arbitrary changes!

---

P.S. Any commit can have any change. Or no change.

A "commit" is a version...a message, a tree, some metadata, and 0 or more parents. In fact it's not even a change/diff/patchset per se. Though will often compare it against its assigned parents. If it has multiple parents, you'd have to choose which to compare. If it has zero parents, you can't compare against any parents.

[ptsneves]

Yes, except git log will show all the commits that got into the branch, while with merge you need git log -m otherwise there are invisible commits(and diffs) in a pretty common workflow. I don’t know why this is the default behaviour.

Git log only shows one tree not parallel trees from the merge.

[paulddraper]

? Not sure what you mean.

git log will show all ancestors.

And git diff shows any difference between two refs.

Nothing invisible unless you deliberately make it so.

[PhilipRoman]

Git log (and many other tools as well) pretend that merge commits do not introduce changes. I learned about it in the hard way when someone managed to implement an entirely new feature, contained within a hidden merge commit.

It's only partially the fault of Git - the entire idea of a merge requires new concepts like 3-way diff, which are not needed for rebased commits. I'm not even sure that most software like GitHub can display such a diff.

[tsimionescu]

The blog post explains it pretty clearly: git log -p doesn't show the diff for those merge commits like it does for a normal commit.

[red_admiral]

The <> version searches the library path (usually /usr/include/* but can be modified with flags) whereas the "" searches the current working directory.

[thaumasiotes]

> I wont claim to understand C and the reason why <> is better than “”. I assume it is.

That one's obvious, you can type <> and you can't type “”.