Comment 2 for bug 1703993

Reading the error carefully it looks like the problem is not classifier itself but one of it's dependencies, "stemmer" which seems to be provided by the package ruby-fast-stemmer.

Afaict there are a few aspects to this

1. Some ruby gems need a native-code component. This component must be built for the right version of ruby.
2. we don't have any mechanism for automatically removing packages that are removed from Debian (I possiblly should implement one but it's more complex than it first appears and i've never got around to figuring out the details) so there is still a libruby1.8 package present.
3. Debian's dependency system doesn't adequately express the complexities of the dependency situation.

The result of this is that the ruby-fast-stemmer package in raspbian jessie is built against the wrong version of ruby but everything looks fine to dependency checking tools.