See "README.htdig.gz" of the KDevelop source package: [quote] What you need to do in order to setup Ht://Dig for using with KDevelop. 1. If you use Ht://Dig v3.1.x patch the sources with this (http://www.geocities.com/alexismikhailov/htdig_3_1_x.diff.zip) file. [/quote]
I committed a new revision of the htdig ebuild that use these patches. A long term solution will come when a new maintainer for the htdig ebuild is chosen. I'm about to submit a bug about that. The ebuild needs serious rehauling. Ideally we'll want it to install a default working config so that kde users get docs searches without extra configuration.