> The typical solution is to become more conservative in how you build things such that you can be sure that Y is always built before X…but typically by making the dependency implicit by, say, ordering the build commands Just So, and not by actually making the dependency explicit to make itself. Maybe specifying the explicit dependency is rather difficult, or maybe somebody just wants to make things work. After several rounds of these kind of fixes, you wind up with Makefiles that are (probably) correct, but probably not as fast as it could be, because you’ve likely serialized build steps that could have been executed in parallel. And untangling such systems to the point that you can properly parallelize things and that you don’t regress correctness can be…challenging.

We had a particularly "fun" instance of this sort of Makefile weirdness back when we used Make for Rust... https://github.com/rust-lang/rust/blob/efec34a95a76212b2324d...

(Discussed on HN: https://news.ycombinator.com/item?id=13655081)