Testing, and lots of it. How else? You can also expand the problem to general flags, not just WIP feature ones, and you have to deal with sellable/licensable fl

Testing, and lots of it. How else? You can also expand the problem to general flags, not just WIP feature ones, and you have to deal with sellable/licensable flags, permission flags, version flags... Big software is going to run into complexity sooner or later. You don't need superhuman skill to manage it but no single person will be able to hold the whole thing in their head. An interesting approach to handling the combinatorial explosion of flags, if you desire to test all possible interactions (even though you don't typically need to) is instead limit yourself to the subset of all pairs of interactions (all-pairs testing).