At Apple, we did indeed use many small repos. Some were even in different SCM systems! It was indeed a nightmare to integrate with “everything on main is broke

At Apple, we did indeed use many small repos. Some were even in different SCM systems! It was indeed a nightmare to integrate with “everything on main is broken, hold off on pulling” being a common multi day experience. At Google we use Blaze which is Bazel and it works very well, as you say. At Meta (where I was before Google) we used Buck2 and it was the best. Much faster and more laptop-friendly than Blaze. It was like Christmas when they switched us over from Buck1. Meta is very very good at “20,000 contributors to this repo”. Google is about 85% as good. Getting work done (especially on mobile apps that take 7 hours to build from scratch) at that scale without these tools would make me jump off the building.