From looking through the source, it seems that apt-build gets the .deb file name and package version from apt-cache's information about the corresponding binary package. If there is no binary package in the cache, apt-build can't do anything. That's kind of sad, because apt-get and apt-src can compile and build packages just fine in that situation.
Can this be fixed (without too much rewriting)? Maybe apt-build could use apt-src's module somehow to get some of the info it needs.
