Sunday, March 1, 2009

Count me out from p2 fan club

I don’t make habit of ranting about technology, but p2 has been driving me up the wall. The old update manager may not have been perfect, but at least it didn’t have the bad habit of preventing installation cases that should work from working.

So we are putting finishing touches on a new version of Oracle Enterprise Pack for Eclipse (OEPE) and it’s time to test various installation scenarios. Eclipse Ganymede SR2 was also just released last week, so we are verifying compatibility with it. One of the basic installation scenarios that we are testing starts out with an all-in-one kit that includes Eclipse Ganymede GA with the previous version of OEPE. The second step in the scenario is to update all of the Eclipse components in that installation. The new version of OEPE requires at least SR1. I let Eclipse search for updates and install everything that it finds. That works. Presumably at this point, the installation should be equivalent to a fresh Eclipse Ganymede SR2 install. The final step is to install the new version of OEPE from a local update site. P2 thinks for a while and then says there are problems that will prevent the installation from working and refuses to go forward.

WTF? I know perfectly well that the plugins we are installing are compatible with Ganymede SR2. They’ve been built using SR2 as the target platform and they work just fine when simply added to the Eclipse installation. Now what? Taking a look at the problems reported by p2, I find about a hundred messages that look like the following.

Cannot find a solution where both "bundle org.eclipse.wst.validation [1.2.0,1.3.0)" and "bundle org.eclipse.wst.validation [1.1.0,1.2.0)" are satisfied.
Unsatisfied dependency: [ 1.0.204.v200708151945] requiredCapability: osgi.bundle/org.eclipse.core.resources/[3.2.0,3.4.0)
Unsatisfied dependency: [ 1.0.204.v200801222138] requiredCapability: osgi.bundle/org.eclipse.core.resources/[3.2.0,3.4.0)
Unsatisfied dependency: [ 1.0.204.v200711140435] requiredCapability: osgi.bundle/org.eclipse.core.resources/[3.2.0,3.4.0)
Unsatisfied dependency: [org.eclipse.wst.command.env.ui 1.0.203.v200709052219] requiredCapability: osgi.bundle/org.eclipse.core.resources/[3.2.0,3.4.0)

These messages don’t make a whole lot of sense. None of them reference plugins that I am trying to install and there is no hint in the messages regarding what actually caused the problem. I looked at one of them in detail to make sure I wasn’t missing something obvious. The second message says that a dependency of plugin cannot be found. That makes sense since it’s a very old version of the plugin that’s not compatible with Ganymede. The question is why p2 trying to resolve that plugin? I look at my installation and I see versions 1.0.304.v200805140230 and 1.0.306.v200810082309. That makes sense. Those versions correspond to what shipped with Ganymede GA and Ganymede SR2. I do not find version 1.0.204.v200708151945 that p2 is complaining about anywhere.

At this point, I gave up trying to make sense of the problem messages and proceeded to blindly try various changes to the way the OEPE update site is constructed to see if I would get a different result. Two alternatives I tried made this scenario work: (a) removing all version constraints from plugin dependencies and (b) reverting to the old-style update site with a site.xml file and no p2 metadata. We still need to do some more testing, but we probably will go with (b) and give up on p2-enabling our update site.

I had reservations about p2 since the poor way in which it was rolled out roughly a year ago, but after a year of fighting with it and this recent experience, I can honestly say (without an ounce of exaggeration) that p2 is the worst regression ever introduced into the Eclipse Platform. I understand the problems that p2 is supposed to solve, but there is just no excuse for destroying the most basic of core scenarios in the process. If it wasn’t ready for Ganymede, it should have stayed as an incubator for a while longer.