If you have a configure step it can fail by default if there is anything to specify explicitly. But otherwise it is nice to have some defaults. In my opinion a

If you have a configure step it can fail by default if there is anything to specify explicitly. But otherwise it is nice to have some defaults. In my opinion a configure script shouldn't do much in terms of detection. It should not silently enable/disable features based only on libraries being present/missing. By default it should try to use lib a and b, if the user wants they could explicitly opt-in to use lib c without lib b, otherwise let it fail. That said it all makes it easier to just use config for make that can be edited. For example config.mk included by Makefile. I learned this trick from Suckless.