[Haskell-cafe] Re: darcs vs. git

[Jason Dagit]

On Wed, Oct 6, 2010 at 7:42 PM, Conrad Parker <conrad at metadecks.org> wrote:
> (subject changed for easy filtering of flamebait, removed libraries@)
>
> On 7 October 2010 10:45, Jason Dagit <dagit at codersbase.com> wrote:
>> At the risk of starting a darcs vs. git discussion I have some
>> thoughts about the tension.
>>
>> On Wed, Oct 6, 2010 at 12:10 PM, Don Stewart <dons at galois.com> wrote:
>> [snip]
>>> == GHC ==
>>>
>>>  * ghc status
>>>        + 50% split in room on moving ghc from darcs to git.
>>
>> I don't see that tension resolving itself easily.  VCS tools are
>> subject to "network effects".  If your friends are using VCS Foo and
>> you want to work with them, then you adopt Foo too.  It's also a part
>> of the toolchain that people tend to have strong opinions about.
>>
>> One possible way to lessen the tension would be good vcs bridge tools.
>>  There have been numerous repo converter projects, some even
>> supporting synchronization.  There is already a git-svn tool.  Maybe
>> there should be a git-darcs (and a darcs-git)?  If a git hacker out
>> there wants to add darcs support to git, I'd certainly be willing to
>> help them get started.
>>
>> Pushing on this a bit more, I'm fairly convinced that darcs and git
>> are dual to each other in terms of underlying models.  As such, I have
>> some ideas on how to unify them/convert between models.
>> Unfortunately, actually having something to use is very far off as the
>> ideas themselves are still immature.
>>
>> As far as I can tell, the main reasons to vote for git:
>>  * Some people simply love git and want to use it for every project
>>  * Git is faster and/or more memory efficient for some operations (most? all?)
>>  * Github
>>
>> As far as I can tell, the main reasons to vote for darcs:
>>  * GHC already uses it (inertia)
>>  * The windows support appears to be more mature (I admit, this is
>> somewhat subjective as neither has a spotless record here)
>>  * Key players, such as the Simons, prefer the darcs UI over the git
>> UI (i.e., some people prefer darcs)
>>  * Darcs 2.x has consistently improved in robustness and efficiency
>> over the last several years, continues to improve, and incorporates
>> ideas from git.  (there is currently an experimental 'rebase' command
>> in the development branch of darcs)
>>  * Cherry picking
>>
>> Note: I didn't mention feature branches as a reason to prefer one over
>> the other.  Both darcs and git support this.  Git uses in-repo
>> branches and with darcs you can simply do a local lazy get.  Some
>> people prefer one mechanism over the other, but the point is they both
>> support the workflow.
>
> I hope they do :)
>
> With darcs, is it possible to refer to various other (local and
> remote) branch names, eg. to do diffs between branches? What I mean is
> that with git, I can do:
>
> $ git fetch origin
> $ git diff my-foo origin/random-bar

You can see the difference of the recorded changes using push or pull.
 If you want a read-only view, add --dry-run.

$ darcs pull --dry-run http://foo.com/random-bar

>
> to see changes between my local branch "my-branch-foo" and the remote
> branch "random-bar" without having to make an explicit checkout of
> origin/random-bar. When the origin repo contains many branches that
> other people are working on, this is a pretty neat way of keeping
> track of those.
>
> I'd really like to be able to get an overview of what branches are
> available (on my local copy and remotely), like with git's various
> graphing tools; I just use a "git log --graph" alias to get a tree
> view in the console:
>
> http://blog.kfish.org/2010/04/git-lola.html
>
> Does something similar exist for darcs?

Yes and no.  Because darcs chooses to keep each branch as a separate
directory it doesn't have a notion that a change can have multiple
children.  Currently when you type 'darcs log' you do see the graph,
it's just perfectly straight.  What you might want to know is, when
can a change come after some other change?  Answering that question is
computationally a bit inefficient.  I think I heard someone suggest it
is quadratic in the number of changes.  You might like this video that
demonstrates a proof of concept graphing tool like you're looking for:
http://www.youtube.com/watch?v=iOGmwA5yBn0

>> I would like to see the tension of darcs vs git for GHC reduced.  I
>> think it ultimately amounts to: Contributors need to be able to use
>> the one they prefer, instead of being forced to use the one GHC devs
>> use.
>
> I agree with that, and I don't mind switching between the two for
> different projects.
>
> Perhaps some standard subcommand aliases would go a long way to making
> that easier though (log vs. changes etc.)

Done.  Already supported in at least one released version :)

In general, you might want to look here:
http://wiki.darcs.net/RosettaStone

Darcs has a fair number of undocumented command aliases to handle
requests like yours.

I hope that helps,
Jason