[news.eclipse.technology.equinox] Re: [p2] Tricks and tips for debugging

[John Arthorne <eclipseng@xxxxxxxxxxxx>]

As you know from recent bugzilla discussions there is work going on to 
improve the usefulness of these messages. In the meantime, the best I 
can offer is the following. There are two main types of problems that 
can occur:

 - "Unresolved dependency" means there is a bundle/feature that 
requires another bundle/feature that is not present in any available 
repository. This can be a bug in the repository you are using, either 
that they are missing a bundle/feature, or missing an associate site 
reference to refer to another repository containing the required 
bundle/feature.

- "mismatch" or "not compatible" - this means there are two things that 
require *different* versions of the same thing, and therefore can't both 
be installed successfully. E.g., plugin A requires plugin C with range 
[1.0,2.0) and plugin B requires C with range [3.0,4.0). There is no 
version of C that will make both A and B happy.

Every time I have seen these errors, it has turned out to be a bug in 
the repository data - either a missing or incorrectly specified 
dependency, or a missing link to an associated repository containing the 
dependency. So if you are seeing these errors with a repository created 
by someone else, I encourage you to enter bugs for it.

I realize that these messages are frustrating and painful to resolve. 
All I can offer as consolation is that this is more painful in p2 
because p2 is actually checking that all dependencies are satisfied 
correctly before installing. With Update Manager, you typically had no 
problems at install time, but the app would fail in equally difficult to 
diagnose ways at runtime when the OSGi resolver did this exact same 
analysis and found the mismatch or unsatisfied dependency (the error 
messages you see in p2 are a result of invoking the OSGi resolver under 
the covers). This didn't bother bleeding edge developers who could live 
with a failure or two, but was a genuine problem in commercial products.
--


Eric Rizzo wrote:
> I'm having a struggle getting our features to install into p2-enabled 
> (Eclipse 3.4 based) applications (Ganymede packages, Rational tools, 
> etc). I keep running into dependency issues, but the output that p2 
> gives when it can't install is less than useful.
> Are there any tricks or techniques that can help an experienced plugin 
> developer figure out why his feature won't install? Anything beyond the 
> cryptic "Cannot find match..." and "Unresolved dependency..." messages 
> that show up in the error log and the p2 UI...
>
> I have to say, this experience is a major step backwards from what we 
> had in the pre-3.4 world; I'm not sure if all the blame lies with p2 or 
> if some of it is due to PDE not being quite caught up, but in any case 
> it is quite disappointing. I'm not new to Eclipse or plugin development, 
> either.
>
> Thanks in advance,
> Eric