Monthly Archives: August 2005

Comparison of Configs/Aliases in Bazaar, CVS and Subversion

When a project grows to a certain size, it will probably need a way to share code between multiple software packages they release. In the context of Gnome, one example is the sharing of the libbackground code between Nautilus and gnome-control-center. The simplest way to do this is to just copy over the files in question and manually synchronise them. This is a pain to do, and can lead to problems if changes are made to both copies, so you'd want to avoid it if possible. So most version control systems provide some way to share code in this way. As with the previous articles, I'll focus on Bazaar, CVS and Subversion Unlike the common operations each system implements this feature in a different way, so I'll go over each one in turn and then compare them. CVS When you run the "cvs checkout module" command, CVS will look in the CVSROOT/modules file for the repository. For example, the file might contain the following: module foobar This would tell CVS to check out the foobar directory from the repository into a directory named module when the user asks for module. If no entry is found for a particular name, the directory by that name is checked out from the repository. To compose multiple modules into a single working copy, the ampersand syntax can be used: module foo &bar &baz bar othermodule/bar With this modules file, "cvs checkout module" would give the following working copy: Working Copy Repository module foo module/bar othermodule/bar module/baz baz Operations like tag, commit, update, etc will descend into included modules, so for the most part a user can treat the resulting working copy as a single tree. If a particular branch tag exists on all the included modules, you can even check out a branch of the combined working copy. There are some problems with the support though: While "cvs update" will update the working copy, it won't take into account any changes in CVSROOT/modules. If you've only got write access to part of the repository, and can't write to CVSROOT/modules, then you can't change configurations. While CVS lets you check out old versions of code, you still use the latest version of CVSROOT/modules. This can make it difficult to check out historical versions of the tree. Since "cvs tag" descends into included modules, you can end up with many branch tags on some modules. For instance, the gnome-common/macros directory in Gnome CVS has 282 branch tags, which makes it almost impossible to feed fixes to all those branches. Subversion Rather than a single repository-wide file describing the module configuration for checkouts, Subversion makes use of the svn:externals property on directories. Any directory can have such a property attached. Each line in the property is of the form: subdir [-rrevnum] absolute-uri-of-tree-to-include This will check out each the given tree at the given sub dir when ever "svn checkout" or "svn update" are used. However unlike CVS, "svn commit" will not descend into the included modules. Some…

End Of Fashion

I went to see End of Fashion upstairs at 78s today for their in-store appearance. The tickets were included with the band's single which was pretty nice. They played for about 40 minutes, starting off with some of their well known songs, and then mixed in a few of the new ones off the album. Towards the end, they did a cover of The Red Sun Band's "Devil Song". After the set the band were doing autographs, so I got the liner notes from my copy of the new album signed by all the band members. I like what I've listened to on the album so far.

Version control discussion on the Python list

The Python developers have been discussing a migration off CVS on the python-dev mailing list. During the discussion, Bazaar-NG was mentioned. A few posts of note: Mark Shuttleworth provides some information on the Bazaar roadmap. Importantly, Bazaar-NG will become Bazaar 2.0. Steve Alexander describes how we use Bazaar to develop Launchpad. This includes a description of the branch review process we use to integrate changes into the mainline. I'm going to have to play around with bzr a bit more, but it looks very nice (and should require less typing than baz ...)

Version Control Workflow

Havoc: we are looking at ways to better integrate version control in Launchpad. There are many areas that could benefit from better use of version control, but I'll focus on bug tracking since you mentioned it. Take the attachment handling in Bugzilla, for instance. In non-ancient versions, you can attach statuses to attachments such as "obsolete" (which has some special handling in the UI — striking out obsolete attachments and making it easy to mark attachments as obsolete when uploading a new attachment). This makes it easy to track and manage a sequence of patches as a fix for a bug is developed (bug 118372 is a metacity bug with such a chain of patches). If you look at this from a version control perspective, this sequence of patches forms a branch off the mainline of the software, where each newly attached patch is a new revision. The main differences being: No explicit indication of what the patch was made against (code base or revision), or what options were used to create the patch. No linkage between successive patches (can be a bit confusing if multiple patch series are attached to the same bug report). So why not just use real version control to manage patches in the bug tracker? The big reason for projects using CVS or Subversion is that only authenticated users can create branches in the repository, and you don't want to require contributors to ask permission before submitting fixes. So this is an area where a distributed version control system can help: anyone can make a branch, so potential contributors don't need permission to begin working on a bug. This also has the benefit that the contributors get access to the same tools as the developers (which is also helpful if they ever become a regular developer). Now if you combine this with history sensitive merging and tell the bug tracker what the mainline branches of the products are, you can do some useful things: Try and merge the changes from the bug fix branch onto the mainline, and see if it merges cleanly. This can tell a developer at a glance whether the patch has bitrotted. This could also be used to produce an up to date diff to the mainline, which can aid review of the changes. Check if the bug fix branch has been merged into the mainline. No need for developers to manually flag the attachment as such. We discussed some of these features in the context of Launchpad at the recent Brazil meeting.

Back from Brazil

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I got back from the Launchpad sprint in São Carlos on Tuesday afternoon. It was hard work, but a lot of work got done. Launchpad is really coming together now, and will become even better as some of the things discussed at the sprint get implemented. One of the things discussed was to formalise some of the development workflow we've been using to develop Launchpad inside Launchpad itself so that it will be usable by other projects. I really enjoyed the time in Brazil. The food and fruit juices were great (especially the ones made from native fruits like Açaí). At the end of the second week, Mark flew us up to Rio de Janeiro for the weekend on his jet: We took a cable car up Corcovado mountain to see the Cristo Redentor statue. There was a great view from the top. Since I was leaving that weekend, I didn't fly back to São Carlos with everyone else. Instead Kiko got a local travel agent to book me a flight directly to São Paulo, so that I could catch my international flight. Unfortunately, when I went to the Varig ticket counter to pay for the ticket there was no record of the booking, which was bad. However, I was able to buy a ticket on the flight anyway (which was due to leave in an hour), which was good. I even ended up paying less for the ticket than I expected. Once I got through security, I found the flight had been delayed, which was bad. After the departure time changing about 3 times, we ended up boarding about an hour after the original listed departure time. This happened to coincide with the listed departure time of the next Varig flight to São Paulo (which had the same gate listed too), causing some confusion. They served chocolate fondue on the flight, which was nice. When I reached São Paulo, it turned out that my checked luggage hadn't, which was bad. I filled out a lost luggage form, and the staff said they'd try to get my bag to the international airport in time for my next flight if it turned up. At the Buenos Aires and Auckland airports, I tried to find out whether my bags had made it onto the flight. The conversations would go something like this: me: Hi, my bag got lost on a previous flight and I want to know whether it made it onto my current flight. Here is the lost luggage form with the bag tag number. them: do you have a bag tag? me: no, they took the tag when processing the lost luggage report. them: well, I can't track the bag without the bag tag. You should have kept the tag. me: ... It was almost the same in Sydney, except the guy at the desk took a look at the form and realised that it had a bag tag number on it (the thing they wanted the bag tag for),…