Dotty is a great project to follow on GitHub if you want to take a look at some very high-quality Scala code. [1]

I like to take a look at /compiler/src/dotty/tools/dotc to whet my appetite from time to time [2].

[1] https://github.com/lampepfl/dotty [2] https://github.com/lampepfl/dotty/tree/master/compiler/src/d...