I'm maintaining mlpack. It is able to generate julia bindings, so on architectures in which julia is available I'd like to generate julia bindings, and this requires julia to be installed at build time. I've set up debian/rules to check if julia is installed, and set configuration options appropriately. Similarly, it seems best to build the package using clang if possible, but if clang isn't available it can be built using GCC (assuming you build single threaded and roughly six hundred mysterious GCC space-saving options are set).
I thought I could accomplish this with build dependencies like Build-Depends: julia | hello, ..., clang | buthead where hello and buthead are stupid little packages that are available on all architectures but would not otherwise be installed. Ugly, sure, but maybe it would get the job done. Nope! The build daemons just try to install julia and clang and fail if either's not available. I've also seen Build-Depends: julia | dpkg, ..., clang | dpkg but that also doesn't work. I could check which architectures have julia, and which have clang, and list them. Build-Depends: julia [amd64 arm64 i386 ...], clang [amd64 arm64 armel armhf i386 ...] but that makes my skin crawl because it is highly non-future-proof and violates all sorts of software engineering principles. Anybody know if there's a good solution to this problem?
