[nightski]

It's not "wildly" different behavior based on the thing it's pointing to. In all 3 cases, the command is pointed at a commit and the behavior is the same. Once you know that branches/HEAD are just named pointers to commits, then it becomes obvious you are always just working on commits and branches/ids/HEAD etc are just ways of referencing them.

[MrJohz]

But branches are not just named pointers to a commit. If they were, then checking out the pointer would be the same as checking out the commit itself. But I can check out a commit and I can check out a branch and depending on which I've done, I'm in two different states.

Either I'm in branch state, where making a commit bumps the branch pointer and means the commit will be visible in the default log output, or I'm in "detached head" mode, and making a commit will just create a new commit somewhere that by default is hidden into I learn what a reflog is. And the kicker is: these two states look completely identical - I can have exactly the same files in my repository, and exactly the same parent commit checked out, but the hidden mode changes how git will respond to my commands.

In fairness, none of this is so difficult that you can't eventually figure it out and learn it. But it's not intuitive. This is the sort of weirdness that junior developers stumble over regularly where they accidentally do the wrong kind of checkout, make a bunch of changes, and then suddenly seem to have lost all their work.

This is one of the ways that I think the JJ model is so much clearer. You always checkout a commit. Any argument you pass to `jj new` will get resolved to a commit and that commit will be checked out. The disadvantage is that you need to manually bump the branch pointer, but the advantage is that you don't necessarily need branch pointers unless you want to share a particular branch with other people, or give it a certain name. Creating new commits on anonymous branches is perfectly normal and you'll never struggle to find commits by accidentally checking out the wrong thing.

[fragmede]

> these two states look completely identical

No they don't. As you noted, one state is "detached head" and any competently set up shell PS1 will tell you that, or that you're on a branch by displaying the name of the branch vs the commit.

> Creating new commits on anonymous branches is perfectly normal

Sorry, that that's an example of more intuitive behavior on jj's partc, you've lost me. I've done that intentionally with git, but I know what I'm doing in that case. For someone new to version control, committing to an unnamed branch doesn't seem like a desired operation no matter which system you're using. What's wrong with requiring branches to be named?

[steveklabnik]

> For someone new to version control, committing to an unnamed branch doesn't seem like a desired operation no matter which system you're using.

We have data on this! I can't cite anything public, but companies like Meta have to train people who are used to git to use tools like sapling, which does not require named branches. In my understanding, at first, people tend to name their branches, but because they don't have to, they quickly end up moving towards not naming.

> What's wrong with requiring branches to be named?

Because it's not necessary. It's an extra step that doesn't bring any real benefits, so why bother?

Now, in some cases, a name is useful. For example, knowing which branch is trunk. But for normal development and submitting changes? It's just extra work to name the branch, and it's going to go away anyway.

[fragmede]

Fascinating. The benefit it brings is you can map the branch to its name. Of the, say, 10 branches you've got checked out, how do you know which branch maps to jira-123 and which one maps to jira-234, or if you're using names, which anonymous branch maps to addFeatureA or fixBugB?

More to the point though, what tooling is there on top of raw jj/git? Specifically, there's a jira cli (well, multiple) as well as a gh cli for github as well as gitlab has one as well. When you call the script that submits the branch to jira/github/gitlab, how does it get the ticket name to submit the code to the system under? Hopefully no one's actually opening up jira/github/gitlab by hand and having to click a bunch of buttons! So I'll be totally transparent about my bias here in that my tooling relies on the branch being named jira-123 so it submits it to jira and github from the command line and uses the branch name as part of the automated PR creation and jira ticket modification.

[steveklabnik]

> Of the, say, 10 branches you've got checked out, how do you know which branch maps to jira-123 and which one maps to jira-234, or if you're using names, which anonymous branch maps to addFeatureA or fixBugB?

The descriptions of the changes. I shared some jj log output in another comment, here it is with more realistic messages, taken from a project of mine:

    @  vvxvznow 
    │  (empty) (no description set)
    │ ○  uuowqquz 
    ├─╯  Fix compiler panic in error rendering for anonymous struct methods (rue-fwi9)
    │ ○  uvlpytpm 
    ├─╯  Stabilize anonymous struct methods feature
    ◆  lwywpyls trunk
    │  Fix array return type unification in type inference

That (rue-fwi9) is the equivalent of jira-123, if I super care about it being obvious, I might put it in the message. But also, I might not, as you can see with the other two. You could also pass flags to see more verbose output, if the first line isn't clear enough, but in general, the convention for git as well is to have that short summary that explains your change, so if it's confusing, you probably need to do better on that.

> Specifically, there's a jira cli (well, multiple) as well as a gh cli for github as well as gitlab has one as well.

These systems do require branches in order to open a pull request. In these cases, I use `jj git push -c <change id>`, which will create a branch name for me, and push it up. This is configured to produce a branch name like steveklabnik/push-mrzwmwmvkowx for a change with the id mrzwmwmv, and ultimately, it's still easier to name locally with m or mr depending on if the prefix is ambiguous. That said, from there I do usually just click the button and then "open pull request" on GitHub, but like, all of these tools (gh is the only one I've used, but I can't imagine that the others do not work, since ultimately, it's a git repo) just work if you want to use them.

Other systems do not even require a branch to submit, and so you don't even need to do this. I would say "submit mr" and it would return me the URL for the created change request. Gerrit does this on top of plain old git.

> how does it get the ticket name to submit the code to the system under?

I haven't worked with Jira in a long time, but with GitHub, if I make a change that fixes issue 5, I put "Fixes #5" in my description, and when the PR is created, it updates ticket #5 to link the PR to that change automatically, no other process needed.

[Zizizizz]

You can name branches in JJ too, they're just called bookmarks.

git checkout main git pull git switch -c jira-234 ... git commit git push -u origin main

jj git fetch jj new main ... jj commit jj b(ookmark) c(reate) jira-234 -r @- jj b(ookmark) t(rack) jira-234@origin jj git push

[steveklabnik]

Right, this is a good point: you can if you want to, or if you're working with a system that requires them.

Just in practice, anonymous branches end up feeling very natural, especially during development, and especially if your code review tooling doesn't require names.

[MrJohz]

They look identical to people who don't know what to look for, and who don't realise that these two states are different, which is the key thing. You can also distinguish them by running `git status`, but that's kind of the point: there's some magic state living in .git/ that changes how a bunch of commands you run work, and you need to understand how that state works in order to correctly use git. Why not just remove that state entirely, and make all checkouts behave identically to each other, the only difference being which files are present in the filesystem, and what the parent commit was?

What's wrong with unnamed branches? I mean, in git the main issue is that they're not surfaced very clearly (although they exist). But if you can design an interface where unnamed branches are the default, where they're always visible, and where you can clearly see what they're doing, what's wrong with avoiding naming your branches until you really need to?

I think this is the key thing that makes jj so exciting to me: it's consistently a simpler mental model. You don't need to understand the different states a checkout can be in, because there aren't any - a checkout is a checkout is a checkout. You don't need to have a separate concept of a branch, because branches are just chains of commits, and the default jj log commands is very good at showing chains of commits.

[fragmede]

My command looks like either:

    fragmede@laptop:(abranch)~/projects/project-foo$

or fragmede@laptop:(abcdef)~/projects/project-foo$

Depending on if abranch is checked out, or abcdef which may be HEAD of abranch is checked out.

If you're having to run `git status` by hand to figure out which of the two states you're in, something's gone wrong. (That something being your PS1 config.) If people are having trouble with that, I can see why switching to a system that doesn't have that problem, it just that it doesn't seem like it should even be problem to begin with. (It's not that it's not useful to have unnamed branches and to commit to them, just that it's not a intro-to-git level skill. Throwing people into the deep end of the git pool and being surprised when some people sink, isn't a good recipe for getting people to like using git.)

> What's wrong with unnamed branches? As you point out, those commits kinda just go into the ether, and must be dug out via reflog, so operationally, why would you do that to yourself. Separate from that though, do you "cd" into the project directory, and then just randomly start writing code, or is there some idea of what you're working on. Either a (Jira) ticket name/number, or at least some idea of the bug or feature you wanna work on. Or am I crazy (which I am open to the possibilty) and that people do just "cd" into some code and just start writing stuff?

VCS aside, nothing worse than opening Google docs/a document folder and seeing a list of 50 "Untitled document" files an my habit of naming branches comes from that. Even though I'm capable of digging random commits out of reflog, if all of those commits are on unnamed branches, and have helpful commit messages like "wip" or "poop", figuring out the right commit is gonna be an exercise in frustration.

As long as you've got something that works for you though, to each their own. I've been using too long for me to change.

[MrJohz]

The only thing that changed in the two things you wrote was `ranch` -> `cdef`. Every other part of that PS1 output was the same.

Now put yourself in the shoes of a git novice and ask yourself if you'd always notice the difference. At least from my experience, they often don't, especially if they're concentrating on something else, it if they're using an IDE and the visual information about which branch/commit is checked out.

I don't think you're crazy, I think you're just too used to this sort of stuff to remember what it was like to still be learning git. When I say people make these sorts of mistakes, I'm thinking about real colleagues of mine who have made exactly these mistakes and then panicked that commits suddenly had disappeared.

Similarly, I think to you, unnamed branches feel like something complicated because in git that are. Git makes it very easy for commits to seemingly disappear into the ether, even though they are still there. But in jj, they don't disappear - they remain very visible, and the log UI shows them in a way that makes it clear where they come from. The default log UI is something like git's --graph output, which means you see how the different commits interact with each other. I really recommend having a look at the output of `jj log`, because I think then it'll be a lot clearer what I mean when I say that it's not hard to figure out what the right commit is.

[skydhash]

> Now put yourself in the shoes of a git novice

Sometimes it seems to me that's only in SWE we allow people to proceed in the workplace without any training. There's enough learning material that people should take a week or something to practice git and not be git novice anymore.

[fragmede]

I missed the formatting on my original comment, but to use real commit names:

    fragmede@laptop:(main)~/projects/project-foo$
    fragmede@laptop:(cf95b5ac22fd...)~/projects/project-foo$
    fragmede@laptop:(opengl_meters)~/projects/project-foo$

Is the difference between these 3 really that subtle? How do you miss that the line lengths are different and that one of them is a pile of letters and the other is a word? I'm not trying to die on some "git is easy to use" hill because it isn't. Just that the difference between unnamed branches and named branches isn't this hidden undiscoverable thing. I don't have access to this dataset of Mr Klabnik's, but apparently it is.

I don't know how much it matters in AI-codepocalypse because I'll be honest, I haven't used git manually in days. AI writes my commit messages and deals with that shit now. (Claude ends a session with "Want me to push it?" and I just reply "yes".

> Similarly, I think to you, unnamed branches feel like something complicated because in git they are.

It's not that working with unnamed branches in git seems complicated, it's that it seems opposite to how I, and by extension, other people work. Now, obviously that assumption of mine doesn't hold true, otherwise we wouldn't be having this discussion, but going back to my Google docs example, staring at a page of documents called Untitled document isn't helpful, so in my mind, there's just a bit of digital hygiene that's necessary under any system.

> I really recommend having a look at the output of `jj log`, because I think then it'll be a lot clearer what I mean when I say that it's not hard to figure out what the right commit is.

You tell me which commit I want from this `jj log` output:

    @  nlvqqyzv [e-mail] 2026-04-15 04:43:07 0d644b5d
    │  (empty) (no description set)
    │ ○  nkuswmkt [e-mail] 2026-04-15 04:43:07 e071e1a5
    ├─╯  (no description set)
    ○  ytyvtmpr [e-mail] 2026-04-15 04:42:51 bd5b4717
    │  (no description set)
    │ ○  srmtuszo [e-mail] 2026-04-15 04:42:35 aa64aea2
    ├─╯  (no description set)
    ○  nrqwxvzl [e-mail] 2026-04-15 04:40:42 c1dbbda3
    │  (no description set)

The effort to label those with `jj describe` what "nrqwxvzl" is vs "nkuswmkt" could just as well be put into using named branches.

Again, I'm not trying to die on a "git is easy to use" hill, because it isn't. My point was that "> these two states look completely identical" isn't true if you setup PS1 to tell you what state you're in.

jj gets a lot of things right, there's no panicking that work got lost. That is a big deal! The emotion toll that the possibility of that happening with git causes on new users is hard to understate. It's hard to not be scared of git after you've lost hours of work after running the wrong command.

I didn't raise $17m to build what comes after git, although I've thought a lot about that problem. Improvements in that area are welcome, and the easier it is for people to work with stacked change sets and branches, globally, can only be a good thing. I can't make everyone else get as good at git as I am (or better!), so I welcome better tooling.

[tom_alexander]

> any competently set up shell PS1 will tell you that

I certainly hope your shell is not running `git` commands automatically for you. If so, that is a RCE vulnerability since you could extract a tarball/zip that you don't expect to be a git repository but it contains a `.git` folder with a `fsmonitor` configured to execute a malicious script: https://github.com/califio/publications/blob/main/MADBugs/vi...

[fragmede]

Might want to let git know. It's been a part of the git source code since 2006. If there were an RCE vulnerability from using __git_ps1, one would hope it would have been found by now!

https://github.com/git/git/blob/master/contrib/completion/gi...

[tom_alexander]

I was able to reproduce it using that script in my PS1 when `GIT_PS1_SHOWUNTRACKEDFILES=1` which triggers a call to `git ls-files`. Without that, it seems to be just calling `git rev-parse` which does not execute fsmonitor.

I was also able to reproduce it with `GIT_PS1_SHOWDIRTYSTATE=1` which invokes `git diff`.

As far as I am aware, this has been brought to the attention of the git maintainers years ago: https://github.com/justinsteven/advisories/blob/main/2022_gi...

[saghm]

> In all 3 cases, the command is pointed at a commit and the behavior is the same

    echo "something" >> foo.txt
    git checkout foo.txt

What's the name of the branch this is pointed at? If I have to run another git command to find out, then it's not "pointed" at it.

[webstrand]

If you don't provide it a <tree-ish> it reads from the index (staged files). So you're right its not really pointed anywhere, since the index isn't a ref.

[saghm]

That's my overall point: the argument itself (with respect to the current state of the repo) is what determines the behavior. I don't think this is anywhere close to as intuitive as commands that only ever accept one "type" of argument (and erroring if it's different).

[nightski]

I stand corrected by this one scenario, but I’ve been using git for over a decade and never found that useful. Just don’t use checkout on a file path, there is no need.

[sswatson]

I find this kind of advice to be a more scathing indictment of an interface than a critic could ever muster: asking users to forego available functionality so that some sense of order can be imposed.

[tom_alexander]

< glances around at all the people telling me to never use `jj edit` >

[saghm]

"Just don't accidentally do things wrong" is also the way to avoid null pointer errors, type mismatches in dynamically typed languages, UB in C/C++. It works, until it doesn't, and in practice that happens pretty quickly. Personally, I like things that have proper safety checks.

[nightski]

Except it's not an unrecoverable error. If you do it all it does is add that file to the working index. No commits are made and no harm is done. So no, I do not feel it's the same as a null pointer exception or type mismatch.

[hollowcelery]

Interesting - I use git checkout constantly, whenever I have a file in another branch or commit that I want to drag into this one wholesale.

[saghm]

It's a useful thing to be able to do! It just fundamentally shouldn't be under one command. To its credit, git did add `switch` (with `-c` for creating a new branch and `-d` for specifying detached HEAD), but after two decades I can't imagine they'll ever get rid of checkout entirely because it was so fundamental for so long, and as long as its there, it's a loaded footgun with the safety off.

[tom_alexander]

If you don't run checkout on file paths, how do you undo changes to specific files that you haven't committed yet? Like you've edited but not committed <foo>, <bar>, and <baz>. You realize your edits to <bar> are a mistake. I'd just run `git checkout <bar>` to revert those changes, what do you do?

It is also really useful when you realize you want <bar> to be the version from a commit two weeks ago. I guess you could always switch to the branch 2 weeks ago, copy the file to /tmp/, switch back, and copy the file into place, but `git checkout c23a99b -- <bar>` is so quick and easy. Or does this example not fall under the "dont run checkout on a path" since it is taking a treeish first before the path?