Build integration is not the main thing that is missing between Livegrep and Code Search. The main thing that is missing is the semantic index. Kythe knows the difference between this::fn(int) and this::fn(double) and that::fn(double) and so on. So you can find all the callers of the nullary constructor of some class, without false positives of the callers of the copy constructor or the move constructor. Livegrep simply doesn't have that ability at all. Livegrep is what it says it is on the box: grep.
The build system coherence provided by a monorepo with a single build system is what makes you understand this::fn(double) as a single thing. Otherwise, you will get N different mostly compatible but subtly different flavors of entities depending on the build flavor, combinations of versioned dependencies, and other things.
