Posted by Tom Moertel
Mon, 02 Feb 2009 17:22:00 GMT
Do you use Emacs? Do you use Git? If so, check out Magit, a delightful Emacs
mode that provides a convenient interface to working with Git. Unlike
many VCS modes, Magit is fully Git-centric: It understands the Git
way of branching, staging, committing, history-rewriting, tagging,
merging, pushing and pulling. It even knows about the reflog and has
some git-svn support.
If you’re a Fedora user,
just install the emacs-magit package. The package is currently in
testing, so install it with the following command:
$ sudo yum --enablereo=updates-testing install emacs-magit
One more thing, Fedora users: please don’t forget to provide
feedback on the package. It’s easy:
- Just visit the emacs-magit page in Bodhi
- Click on the package you installed (e.g., the Fedora 9 or 10 flavor)
- Add a comment, selecting “Works for me” or “Does not work” as appropriate
Hack on!
Posted in programming
Tags emacs, fedora, git, magit
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Posted by Tom Moertel
Mon, 10 Dec 2007 21:52:00 GMT
About three years ago, I switched to
Darcs
as my primary source-code management system. It was simple,
intuitive, and powerful, and it made managing my projects more fun and
less frustrating than any centralized VCS ever had. That it was
written in Haskell, one of my favorite programming languages, made
it even better. I was hooked.
Since then, the distributed SCM landscape has changed. Darcs hasn’t
improved much, but its competitors have made long strides, especially
Git and
Mercurial. Both
are crazy fast, vigorously developed, and widely used on large, highly
active real-world projects, such as the Linux kernel and Mozilla 2.
In comparison, Darcs has
stagnated.
When I started working for a new company recently, I had to consider
whether to advocate Darcs or something else. In the end, I decided
that Darcs would be a hard sell. Nobody else at the company uses
Haskell, and having to explain how to avoid the occasional corner
case
seemed liked a losing proposition.
After researching and playing around with Git and Mercurial, I settled
on Git. I like Git’s underlying hashed-blobs model better than
Mercurial’s revlogs, and Git seems to have slightly more development
momentum. Still, it was a close call. Either choice would have been
completely reasonable.
Missing Darcs
When I started using Git on real projects, the one thing I really
missed was the ability to easily amend earlier patches, something
Darcs made trivial. Let me
explain. The typical development workflow goes something like this:
- Checkout copy of upstream code base.
- Implement feature X.
- Commit.
- Implement independent feature Y.
- Commit.
- Implement independent feature Z.
- Commit.
- Push new features back upstream.
Now, what really happens is that when I’m implementing Y or Z,
I’ll realize that I made a mistake in X. The trick is then
fixing X so that my fix is part of the changeset/patch for X that
ultimately gets pushed upstream in the last step. That way, the
upstream folks will see only a single, clean patch for feature X – not
a mishmash of patches that together represent X.
In Darcs, amending the original patch is easy because its patch theory
lets me tweak the patch for X independently of the other patches.
Darcs will simply ask me which patch I want to amend, and I’ll select
the orignal patch for X:
$ emacs # fix X
$ darcs amend-record # amend original patch for X
Mon Dec 10 14:43:13 EST 2007 Tom Moertel <tom@moertel.com>
* Implemented Z
Shall I amend this patch? [yNvpq], or ? for help: n
Mon Dec 10 14:42:12 EST 2007 Tom Moertel <tom@moertel.com>
* Implemented Y
Shall I amend this patch? [yNvpq], or ? for help: n
Mon Dec 10 14:41:46 EST 2007 Tom Moertel <tom@moertel.com>
* Implemented X
Shall I amend this patch? [yNvpq], or ? for help: y
hunk ./x 1
-X1
+X2
Shall I add this change? (1/?) [ynWsfqadjkc], or ? for help: y
Finished amending patch:
Mon Dec 10 14:43:25 EST 2007 Tom Moertel <tom@moertel.com>
* Implemented X
That’s it. The exact same process will work regardless of when I
realize I need to fix X: before I start Y, while I’m implementing Y,
after I’ve committed Y, while I’m working on Z, or after I’ve committed
Z.
Learning to love Git
With Git, however, I can amend a commit only if I haven’t committed anything else before making my fix. In Git’s mind, Y depends on X, and Z
depends on Y, even if they really are independent of one another.
So if I commit the original patch for X and then immediately realize I
need to make a fix, before I start working on Y or Z, it’s easy:
$ emacs # implement X
$ git commit -m 'Implemented X'
# discover problem in X
$ emacs # fix X
$ git commit --amend # amend original patch
More typically, it’s only while I’m working on Y that I’ll
realize I need to fix X. Then it’s more complicated
to amend the original commit:
$ emacs # implement X
$ git commit -m 'Implemented X'
$ emacs # start working on Y
# discover problem in X
$ git stash # stash away half-completed work on Y
$ emacs # fix X
$ git commit --amend # amend original patch for X
$ git stash apply # restore work on Y
$ emacs # continue working on Y
While not as convenient as Darcs’s workflow, it’s perfectly workable.
Now let’s consider another fairly typical case: I commit X and Y and
then start working on Z before I notice the problem in X. I used to
think that Git couldn’t handle this case, but it can, thanks to
git rebase --interactive:
$ emacs # implement X
$ git commit -m 'Implemented X'
$ emacs # implement Y
$ git commit -m 'Implemented Y'
$ emacs # start working on Z
# discover problem in X
$ git stash # stash away half-completed work on Z
$ emacs # fix X
$ git commit -m 'Fixed X'
$ git rebase --interactive HEAD~3 # see comments below
$ git stash apply # restore work on Z
$ emacs # continue working on Z
The
git rebase --interactive command is
powerful. What the
command does, as called in the snippet above, is invoke my editor of
choice on a text file describing the last 3 commits (that’s the
HEAD~3 part):
# Rebasing 3ad99a7..b9a8405 onto 3ad99a7
#
# Commands:
# pick = use commit
# edit = use commit, but stop for amending
# squash = use commit, but meld into previous commit
#
# If you remove a line here THAT COMMIT WILL BE LOST.
#
pick 0885540 Implemented X
pick 320b115 Implemented Y
pick b9a8405 Fixed X
I can then edit the file to reorder, merge (squash), and/or remove
the commits. In this example, I want to merge the fix for X into
the original commit that implemented X. So I edit the file like so:
pick 0885540 Implemented X
squash b9a8405 Fixed X
pick 320b115 Implemented Y
Then I save the file, at which point Git takes over and makes the
requested changes, merging the fix for X into the
original commit for X. Now the log shows the original implementation
and fix as one commit:
$ git log
commit f387d650976246c0854d028b040cca40e542be56
Author: Tom Moertel <tom@moertel.com>
Date: Mon Dec 10 15:11:26 2007 -0500
Implemented Y
commit 82a1c849ffd1bd688d5bc9d99be0e63548a89c4c
Author: Tom Moertel <tom@moertel.com>
Date: Mon Dec 10 15:13:03 2007 -0500
Implemented X
Fixed X
commit 3ad99a7ef537b7ae99e435e0d2b4b0d03de92c65
Author: Tom Moertel <tom@moertel.com>
Date: Mon Dec 10 15:11:14 2007 -0500
Initial checkin
Once I figured out how to use git rebase --interactive, I stopped
missing Darcs and started loving Git.
Posted in programming
Tags darcs, dvcs, git, haskell, scm
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Posted by Tom Moertel
Thu, 25 Oct 2007 20:26:00 GMT
On the Darcs Users mailing list, I ran across an interesting thread: practical differences between darcs’ patch model and git/mercurial’s?
Among the interesting points of discussion:
- Do the mechanics that give rise to Darcs’s strong cherry-picking abilities also make it susceptible to naughty time-complexity behavior?
- When you merge non-conflicting changes in Git or Mercurial, you must record a merge patch, which binds the two in the development timeline, but in Darcs the respective patches are free to commute. Which behavior is better for real-world development?
If you’re interested in distributed source-code management, it’s an interesting thread to follow.
Posted in programming
Tags darcs, git, mercurial, patches, vcs
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