Why a small team chose Mercurial. | Hacker News Reader

Why a small team chose Mercurial.

ninthdivision.com

37 pointsatrain3430 comments

After using git and then using Mercurial, it was clear that Mercurial was a better fit for our company, how we develop. For educated people on git/hg, these might be a surprise. But the people still considering git or hg its a good look.

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This misconception always bothers me:

"In Mercurial you can’t change previous committed code. In git you can change the past commits in the repo. I am sure there are cases where the linux kernel needs to do this (I can’t think of any), but this is some we don’t even want to have the option to do."

Yes, you certainly can change commits in hg. The tools to do it in git are a bit more refined, but there's no fundamental difference here.

I don't want every failed, unbuildable, safety-net commit making it into my project history. I want it to be possible for people to understand change.

For example, here are the last few commits from my primary work project: http://pastebin.com/BiNpP08s

In a week from now, will you need to see the four different attempts it took to get that last change right? If so, you can always follow the code review link and see the discussion that went on there and how it shaped into that file change, but anyone who makes actual good use of their project history will get frustrated pretty quickly at thought-free changes.

The difference is not fundamental, no. It is a difference in philosophy and interface that discourages modifying history.

The question is: Why would you commit (to a stable branch) when your code doesn't build or pass tests? Why would you want to eliminate a state where you made something that worked? I don't see the appeal in modifying history.

If you just need to save some partially working state, etc. you can use patch queues- They make much more sense here.

I haven't used mercurial in anger, and mostly use subversion instead (because that's what my workplace uses at the moment), but:

1) sometimes you commit by accident. This happens to me a few times a year, from hitting the up arrow the wrong number of times and pressing enter.

2) sometimes you say something in a commit message that turns out not to be true, or is just a typo, and especially if you're using commit messages to tie commits to tickets in your bug tracker, this can make code show up on the wrong ticket, or not at all, which is quite confusing for a later maintainer.

It is trivial in Mercurial to back out the last commit: hg rollback

I use it all the time to fix typos, add a file I forgot to add, or whatever. Once you push, it is more difficult, but I try not to push my code until it works. I also commit only tested chunks of code, so that is the "unit of work" I aim for.

The equivalent in git is something stupid, I have to look it up every time: git reset --soft HEAD^

That's intuitive!

git commit --amend

It sounds as though the equivalent mistake would be an accidental push. Good to know that git and mercurial allow you to fix things, in any case.

git push is reversible, too: http://news.ycombinator.com/item?id=2079967 (and note my correction below that simplifies things)

git reset HEAD^ (soft is the default option) is actually pretty intuitive once you're used to git. You're reseting the index to the state it was one commit ago (which is what HEAD^ means. That comes up a lot.)

And if you really forget it often, add this to your ~/.gitconfig:

    [alias]
      rollback = reset HEAD^

Now you can run `git rollback`

I know what HEAD^ (and HEAD^^^^^ or whatever) mean.

The fact that I have to make aliases for commonly used tasks is not a point in git's favor to me.

Do you really uncommit that frequently? I just either amend my commits or keep adding new commits and squash them later.

The point is that you can make just about any workflow with git. The ones that git users less commonly use may not be have easy toplevel commands. People already complain about how many toplevel commands there are with git.

> The question is: Why would you commit (to a stable branch) when your code doesn't build or pass tests?

Because:

a) It's not a stable branch. It's my dev branch on my local box that nobody else can see.

b) I feel like it and there's no penalty. I can go back if something is wrong.

c) The next thing I'm going to do is risky. I should save where I am just in case I'm wrong.

> Why would you want to eliminate a state where you made something that worked?

Because it may not be meaningful and it may not work. In the above case, what value do you gain from the three revisions of that change that were incorrect? When it hit code review, there were problems with it. We fixed them. Why would you publish code that is known to be incorrect (since we figured that out during code review)?

> I don't see the appeal in modifying history.

I don't see the appeal in a history full of "Oops, I forgot to add this file to the last commit," and "build fix" and "The author wrote this on Solaris, but I need a small change in the Makefile for Linux."

If there's one logical change, having several commits where you just didn't get it right only adds confusion.

> If you just need to save some partially working state, etc. you can use patch queues- They make much more sense here.

Are you saying that because that's the tool you were offered or because you actually believe it's the best way to do things?

I used mercurial very extensively before I started using git (which I have also used very extensively). Most of my time was spent in mq capturing state of work in progress. That really sucked.

Now, I just commit whenever I feel like it, and then before I publish code, I update the commit messages, squash distinct changes that represent a single logical change that shouldn't be broken up, break up commits that represent more than one logical change that shouldn't be lumped together and just generally tidy things up so the reviewers and future developers tracking back bugs can make sense of things.

Then I test it: http://dustin.github.com/2010/03/28/git-test-sequence.html

> c) The next thing I'm going to do is risky. I should save where I am just in case I'm wrong.

a and b are not really reasons /to/ commit a broken state. On c: If the next thing you're going to do is dangerous, I'd say it's a separate "thing" and either 1) commit the stuff you have in a working state or 2) shelve/stash/qimport it if it's not done and you need to do the dangerous work first, which is why I mentioned patch queues.

Thus, purposeful broken commits are eliminated.

> I don't see the appeal in a history full of "Oops, I forgot to add this file to the last commit," and "build fix" and "The author wrote this on Solaris, but I need a small change in the Makefile for Linux."

hg rollback/backout are intended for "oops, I forgot to add this file to the last commit." There's no need to leave those commits in, unless the problem isn't discovered for a while, which is when modifying history makes sense.

Patch queues are most definitely not just "the tool I was offered." They are a rather powerful way to deal with commits as a stack, and I've never been bogged down "capturing state of work in progress."

---

There's nothing really wrong with git's workflow, but there's nothing wrong with mercurial's either. That's all I'm saying - "it is a difference in philosophy and interface that discourages modifying history" that I happen to prefer.

If it's important enough to be committed, it's important enough to be remembered.

Do you make the same judgment about saving files? If it's important enough to be saved to the filesystem, it's important enough to be remembered forever?

What about general edits in your editor? If it's important enough to have been typed so undo in my editor works, it's important enough to be part of the project history so someone else can see my typos when they're (as I've heard used as an argument for why you should never squash commits) tracking down a bug they can figure out the train of thought that led to that work?

What about rewriting a topic branch before merging it?

I've been using Mercurial for a few years and am now turning to git (one week in, so I won't say much about it) for a very specific and fundamental reason: short lived local branches.

Say you have a repository, fix a few bugs on it, and now you want to work on a crazy feature. What you need is a short lived local branch, because you don't know if crazy feature even makes sense. Unfortunately, there is no built in way to do this in hg. [1] Deleting a branch is not a fundamental concept in hg, and so the advice is to create a new local "clone" of the entire repo. [2] Great, now you have to change the config files for your dev environment to point to a new folder just so you can test out crazy feature. Also, by default all your branches get pushed (although hg will complain about creating remote branches).

In practice, all this turned "branching" into an expensive concept in my mind. That's bad, very bad.

I still prefer the hg elegance and ui to git -- even the output of "hg st" vs "git status" tells a great deal about the philosophy behind both. However, I think hg got branching wrong and that is a fundamental flaw that no amount of elegance at the UI level can compensate for.

I remember when I was making my first choice between hg and git and the advice was "they're pretty much the same, pick one." I think that advice is incorrect based on what I've said above.

[1] http://mercurial.selenic.com/wiki/LocalbranchExtension [2] http://mercurial.selenic.com/wiki/PruningDeadBranches

I use patch queue[1] to manage these short lived branch, and it works for my purpose. You just pop the patches and delete them all when you want to prunge the branch. It also make it easy for others to review your code.

If these short-lived branch will be merged back shortly. Bookmark is another alternatives.

[1] http://mercurial.selenic.com/wiki/MqExtension [2] http://mercurial.selenic.com/wiki/BookmarksExtension

I'm aware of both. Personally I find this to be an inferior solution. Using a patch queue as a local branch just feels wrong. Neither is using bookmarks an effective solution. Both solution make the decision to branch a much more deliberate process, and in the end you still don't get a branch that is equal to its peers.

As the result, in hg, you have to decide in advance "what kind of branch" it will be -- or you have to get in the habit of using mq's for everything -- and this just not a natural experience especially for a DVCS where branching is just fundamental.

Mercurial bookmarks are roughly equivalent to Git branches. They are local only unless you explicitly push them and you can delete them when done.

I love Mercurial, but I agree with this. I tried using the bookmarks extension with a colleague who wanted to use branches this way and we had trouble figuring it out. Definitely not as easy as git (though getting new remote branches with git is another thing that drives me crazy and I have to look up every time).

git stash is another thing I really like about git. There are hg alternatives but they are not as easy to use (and if you go the mq route things become so complicated you might as well just use git).

Before this devolves into a git versus hg holy war by people who never read the linked blog post, I'll point out that they chose hg over svn. It's mainly a cheerleader piece for DVCS with the git versus hg choice being a minor point.

yes, please read the linked blog post. they used both hg and git quite a bit but found hg easier to host, use and move over from subversion (convert repos but also command line).

so yes, cheerleader piece you are right on that. not much cheerleading for hg these days.

>> not much cheerleading for hg these days.

Joel Spolsky seems to like it: http://hginit.com/

I switched from svn to hg for personal stuff too. Like the author of the blog post, I looked at git and found that it was nonintuitive. hg commands are close enough to svn commands that I felt more comfortable sooner.

I don't really get the big issue with branches in svn though. Branches and tags are "cheap" operations in svn, and making personal branches, etc. was something I used to do. Merging back into trunk was never a huge issue either. Maybe I've been lucky; also our team was not very big and different people weren't often working on the same source files at the same time.

Pretty good; liked that they didn't just say "HG GOOD, GIT BAD". I'm confused about the git learning curve though; I started using git on my own this summer, and I was able to immediately pick up the commands I needed to get by literally the day I started. I'll admit I don't have to host repositories, like they would in for their company; but for simply using git as a developer it was very painless.

Having taught people both systems, I will assert, based on my personal experience, that while some developers can certainly pick up Git relatively painlessly, picking up Mercurial objectively requires less time, and leaves users less likely to get into a state that they are unsure how to exit. This is purely based on my own personal experience, and I have not scientifically codified the learning time in double-blind testing or whatnot, but it's a data point based on more than just my own personal meandering attempt to learn the two tools.

EDIT: I am not making a value judgment here. It's harder to learn to fly a plane than drive a car, but that hardly makes the car better than the plane or vice-versa. It's just a recognition that their learning curves aren't identical.

Having introduced git to a few groups (and some hg), I found that the main thing that makes hg easier to learn is that hg mimics some of the same names of commands as cvs/svn. However, once they understand what is going on in git, the aha moments start to show up, and the really complicated stuff becomes easy.

Some of git's learning curve reputation is historical. Some good effort as been put into making git less arcane.

altogether a means to an end, mercurial and git are both good. i personally use mercurial. have worked with git in the past and was having trouble with the gerrit web front end and the fact that it required java.

i also use bitbucket and since having been bought by atlassian, was able to get lots of free private repositories. i think some people mentioned that they accidentally left cookie secrets in their code on a public github project.

i'm still too early in development to get into the perceived branching woes that others are talking about, but i'll let you know when i get there.

The fun thing about lightweight, painless branching is that once you start to incorporate that into your workflow, it's never too early in a project to use it. Lately every new feature or fix I start to work on begins its life in a topic branch. You never know when you're going to be interrupted or need to switch contexts to work on something else (or even just scrap the whole idea) so having your repository mirror your mental process in a completely seamless way is invaluable.

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