Right now, mercurial.eclass does declare HG_REV_ID as a local variable and use it only for output. I'd appreciate if it could export it instead, thus making it possible to lookup the exact revision of a package from environment.bz2. This is required in order to provide complete Mercurial support in app-portage/smart-live-rebuild. Related bugreport: http://github.com/mgorny/smart-live-rebuild/issues/#issue/2
Done, HG_REV_ID is being exported from eclass.
Thanks.