We've been working with JetBrains on that part. The compose plugin is using a facility that allows compiler plugins to intercept method calls and do their own work there that permits this. It's a work in progress.
We've got a bunch of posts coming explaining some more of the process of how we got here. As a starting point I agree with you, the bar for this sort of thing is extraordinarily high.
05/21/2019, 2:10 PM
And it's worth emphasizing what Adam said, that we are working very closely with JetBrains