[kevincox]

I don't think it is very "magic".

The VFS gets you a few main benefits.

1. You can lazy download and checkout data as you need it. Assuming your build system is sufficiently realized to hide the latency this will save a lot of time as long as accessed data is significantly less then used data (say <80%).

2. You don't need to scan the filesystem to see what has changed. So things like commits, status checks and even builds checking for changes can target just what has actually changed.

Neither of these are particularly complex. The hardest part is integrating with the VCS and build system to take advantage of the change tracking. Git has some support for this (see fsmonitor) build I'm not aware of any build systems that do. (But you still get a lot of benefits without that.)