I'm trying out Trac for a side project. I like it because it's both a tracker and a wiki, and your tickets each have a wiki page.

It has a roadmap feature where you define milestones, and you can assign tickets to a milestone for planning and triage.

One thing I haven't figured out is how to block closing a ticket on the closing of another ticket. That's all I'm missing from it so far. Anyone? Is there a feature or plugin for that, or a practice, that I've missed?

Edit: s/to a roadmap/to a milestone/