Difference between revisions of "Darcs vs. Git"

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What makes Git so popular even amongst Haskell programmers?
= Darcs Resources =
I remember that GHC team switched because Darcs had problems with merges
and became slower as the history of a project evolved.
On the one hand this is a problem of Darcs that must be improved.
On the other hand GHC is a big monolithic project
which is not only a problem for a versioning system
but is also unfortunate for users who want to use selected subsystems of GHC,
like the parser, the module system, the type checker, the optimizer, the code generator and so on.
In the meantime I worked with Git for several projects.
* http://darcs.net/ Main site
I hoped that if I work for those projects
then their maintainers could help out with Git problems.
I expected that if they switch from Darcs to Git
then they made good experiences with Git.
This is not the case.
In those projects nobody could give satisfying solutions to even common Git problems.
Thus I started to collect the issues I frequently have with Git.
They make me stay with Darcs for the projects
where I have the choice of the versioning system.
* http://darcs.net/FAQ
== darcs replace ==
* http://www.haskell.org/haskellwiki/Darcs
Darcs can replace identifiers, Git cannot.
* http://en.wikibooks.org/wiki/Understanding_Darcs/Patch_theory_and_conflicts
I often rename identifiers.
The identifier substitution of Darcs both saves space
and allows for smooth merging.
In Git renamings of identifiers look like you alter a lot of lines here and there.
I don't think that Git can easily implement that feature,
because it has no notion of a patch.
== darcs check --test ==
= Git resources =
Darcs lets you easily run a test suite after every commit.
* http://git-scm.com/ Main site
Usually I register
: <code>cabal configure && cabal build && cabal haddock && cabal test</code>
* http://git-scm.com/book
as a darcs test.
* http://gitref.org/
After recording a patch,
darcs unpacks the repository temporarily in the state after adding the patch.
Then it runs the test suite within that temporary copy of the repository.
If you add a file the Cabal description but forgot <code>darcs add</code>
or vice versa, then the darcs test will quickly spot the problem.
This almost not possible with Git.
* http://bramcohen.livejournal.com/74462.html
It could certainly be hacked into <code>.git/hooks/pre-commit.sample</code>,
but the crucial feature of running a test
is to reject a commit if it does not pass the tests.
If there is a way in Git then it is by far more complicated than in Darcs.
I see no reason why Git does not support pre-commit tests properly.
= GHC's switch from darcs to git =
== Pushing to the wrong repository ==
* http://www.haskell.org/pipermail/glasgow-haskell-users/2011-January/019752.html
It is very easy in Git to push commits
* http://www.reddit.com/r/haskell/comments/ezgvs/rfc_migrating_ghc_development_to_git/ interesting thread
to an unrelated repository or to the wrong branch of a repository.
And it is cumbersome and dangerous to get rid of the wrongly pushed commits,
if operating in a bare remote git repository.
In a bare git repository you cannot use commands like 'git branch'
that you are familiar with in a working copy.
In darcs this cannot happen so easily
since normally darcs asks you which patch to push.
This way you can see early if something gets wrong.
== Pushing to repositories with working files ==
Pushing to a bare Git repository requires that you enable
the <code>post-update</code> hook. Why?
Pushing to a Git repository with working files is even more cumbersome.
I like to point people to certain files in a remote repository,
e.g. by an HTTP URL.
This requires automatic updates of working copy files when pushing to the remote repository.
If you try to push to a Git repository with working files
that is not prepared for this action
then you get a message that it is not possible
and what alternatives you have.
Among the alternatives there does not seem to be one
that automatically updates working copy files after a push.
Maybe it is possible in Git, but it requires at least some effort.
In darcs there is no distinction between bare repositories and working copies.
Working files are always automatically updated.
== Pull and stash ==
I often have locally modified files when pulling patches from somewhere else.
With git this needs at least three steps:
git stash
git pull
git stash pop
With darcs it is just <code>darcs pull</code>.
Git does not make backup files if there is a merge conflict, Darcs does.
== Branches ==
When working with Darcs I missed branches.
I thought it would be a good idea
to let the versioning system manage my attempts to solve hard problems in my projects.
I expected that if people clone my repository or pull patches
that they access all branches of my repository simultaneously.
I hoped that native support for branches
would be better than creating a new working copy for every branch.
Maybe Git got branching wrong
but today I am uncertain whether there is a good way to support branching
other than not supporting branching.
Git does not handle all branches of a repository simultaneously.
Git can push and pull commits from one local branch to another remote branch and back.
It is not so simple in Git to switch a branch if there are local modifications.
You need to <code>git stash</code>.
And what about the open text editor
that contains a file that gets modified by switching a branch?
Sure, modern text editors warn about changes on the file storage
but it is still easy to accidentally overwrite a file on one branch
with the contents of that file on another branch.
What I actually ended up is to create one Git working copy for every branch.
This way, switching between branches is easy.
This is precisely the way I work with Darcs.
== GitHub ==
github sucks, looping scripts, pull requests, how to get a git repository
== Merging ==

Latest revision as of 18:50, 18 June 2014

Darcs Resources

Git resources

GHC's switch from darcs to git