Here are some resources for new and experienced Scala hackers, to help in their contribution to the Scala language!

• official:
  • Scala repo README
  • Scala Hacker's guide
• talks:
  • Jason Zaugg (retronym) - Scala survival guide talk and code from the talk (2015)
  • A deep dive into Scalac slides by Chris Birchall (2015)
  • Paulp's Scalac Internals talk (2012)

• Scala Reflection Guide
  • especially: Symbols, Trees, and Types
• Def Macros Guide

• Scala Compiler Internals (videos by Martin Odersky)
• Scala Internals Wiki
• Miguel Garcia's Scala Compiler Corner Reloaded (mainly about back end)
• Miguel Garcia: A new backend and optimizer for Scalac
• Writing Compiler Plugins (2008/9)

• Dotty, the repo and Dotty - getting started wiki

• Michael Schinz - Compiling Scala for the JVM
• Mirko Stocker - Scala Refactoring (Master's thesis)
• Internals of Scala annotations
• Scalable Component Abstractions (2005)
  • section 4 is "Case Study: The Scala Compiler"

Anything else? ;-) Feel free to fork this or send a PR my way!