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devel:darcs

DokuWiki darcs repository

Until January 2010, the DokuWiki sources were managed through Darcs1). We now use git and you should refer to the git page on how to contribute to DokuWiki. Because some DokuWiki plugins are still maintained in darcs, this page remains here for reference purposes.

Darcs is a replacement for CVS. Darcs is simple to learn and use, with a powerful new approach to meet the needs of today's distributed software projects. Darcs is decentralized, based on a “theory of patches” with roots in quantum mechanics. Darcs is free software, licensed under the GPL.

How to use darcs

Instead of repeating things that were said elsewhere I just want to give some pointers:

Using darcs for DokuWiki

To fetch the current development version of DokuWiki use the following command (This creates the directory dokuwiki for you):

darcs get --partial http://dev.splitbrain.org/darcs/dokuwiki

To update an existing checkout use this command from within the DokuWiki directory:

darcs pull

When you create a new source file, use this command to add it to the darcs repository:

darcs add somenewfile

When you're finished with your changes use:

darcs record

This will scan your local darcs repository to find the changes that have occurred and will locally “commit” your changes so that they are not overwritten by a pull. Unlike CVS it doesn't actually send the files anywhere at this point though. It's more like a “local tag” for your own copy of the code.

To get your changes included in the official tree, create a patchfile:

darcs send -o my_doku_patch_file

This creates a patch file that can be mailed manually to the mailinglist.

Tips and Tricks

  • :!: Always pull before starting to work on new patches, to make sure you don't create conflicts.
  • :!: Never use the amend-record command after you sent a patch with darcs send this will most likely create conflicts! Instead just create another patch which fixes the first one.
  • Make sure your editor does not change line endings (from Unix LF to DOS CRLF), this would result in a complete file replace, instead of a small patch because each line was changed.
  • Make a patch for a single feature. When you worked on two different features (eg, a language fix and a function update), record two patches, with one for each feature. darcs makes that easy for you by asking what to include in the patch.
  • Patches should be sent to the mailinglist and you should explain what they do and why.
  • Do not worry about the patch file size. darcs patches tend to be big even for small changes. Space is cheap.
  • Some mail clients/server mess with plain text attachments breaking the crypto hash of the darcs patch. To be on the safe side, zip, tar or gzip your patch before emailing it

Mixing the official tree with own patches

Because each checkout is its own repository people can keep their own modifications as patchsets and can still update from the “master repository”.

So how does this work in practice? Darcs can't do magic, if you change something in your local repository and the same is changed in the “master repository” you'll get a conflict - there is nothing any RCS can do about this.

However if you make minor changes that aren't touched in the upstream version you should get no problem when updating from the official repository. This is because darcs just applies patches. As long as darcs finds enough context to apply the patch it should work.

For example if you add some HTML to one of the functions in html.php you still should be able to apply the official patches to html.php by doing a simple darcs pull.

Maintaining a stable version with darcs

Darcs isn't only for DokuWiki developers, it can be used to get the latest stable version and to update to the next stable version when it is released.

To get a particular release of DokuWiki (replace yyyy-mm-dd with the date of the release, e.g. 2006-11-06):

darcs get --partial --tag="release yyyy-mm-dd" http://dev.splitbrain.org/darcs/dokuwiki

Unfortunately darcs contains a bug that causes problems when –partial and –tag are used together. Until the bug is fixed, it is better to leave out the partial and just use:

darcs get --tag="release yyyy-mm-dd" http://dev.splitbrain.org/darcs/dokuwiki

To update to a specific release, a release candidate or the latest release (stable):

darcs pull --tags "release yyyy-mm-dd" --all --quiet
darcs pull --tags "release candidate yyyy-mm-dd" --all --quiet
darcs pull --tags "release stable" --all --quiet

The –all –quiet ensures all patches are applied and darcs gets on and does its stuff without reams and reams of messages.

Updating when you have customized DokuWiki

If you have made your own changes to DokuWiki's core codebase, it may be better to leave off the –all –quiet switches and accept each patch interactively, e.g.:

darcs pull --tags "release yyyy-mm-dd"
darcs pull --tags "release candidate yyyy-mm-dd"
darcs pull --tags "release stable"

At the end of the patching process Darcs will let you know if there were any conflicts between your changes and the patches applied to make the new version. You can then examine the files in question and make any necessary changes.

You can use the following command to keep track of the changes you have made to DokuWiki:

darcs whatsnew

When run interactively the revert command will do something similar and give you the opportunity to remove your changes if they are no longer required.

Why Darcs?

So why did I choose Darcs over CVS, Subversion or arch?

Darcs has, in my opinion, several advantages:

  • it needs no special server for anonymous readonly access – any HTTP server is enough
  • it can manage directories (same goes for SVN and arch)
  • it is fully distributed, each checkout is its own repository (same goes for arch)
  • no complicated naming scheme is needed (as in arch)
  • independent patchsets (see below)
  • makes contributing and applying contributions easy (through darcs send)

There are some disadvantages though:

  • it's a little buggy sometimes (though not critically)
  • it's relatively unknown yet

What I like most are the patchsets. Because each checkout is its own repository people can keep their own modifications as patchsets and can still update from my “master repository”, see the above section for a short explanation.

1)
David's advanced revision control system
devel/darcs.txt · Last modified: 2010-03-13 15:45 by 84.132.221.218