…ncies are in the gemspec, a gem's Gemfile should just use the gemspec method' best practice as stated by Yehuda
… to bundle before raking. all other development dependencies are handled by bundler.
… overriden for cases like switching to username & password, requiring fewer files to change. this breaks the before_filter :authenticate API that used to exist, which has been replaced with the more aptly-named before_filter :authorize.
Diesel looks within features/engine for the generator and needs to be included with the gem for those features to be installed successfully.