One of the approaches I'm currently investigating and have high hopes for composition, pure functions, and explicit two-way dependency tracking. I'm trying to put this to the test in my work. The idea is that I hope even huge software can be decomposed into smaller independent (meaning all the dependencies are explicit) chunks with pre- and post-conditions. So fixing many bugs could boil down to navigating to the code responsible and fixing it there. It's too early for me to say how it'll work in reality, but I will find out with time.