SBT: 'compiler-interface' not yet compiled for Scala 2.12.2. Compiling...

SBT FAQ: What does the message, “'compiler-interface' not yet compiled for Scala 2.12.2. Compiling...” mean?

Answer: I don’t know all of the nitty-gritty details, but the short version of the answer is described in the SBT docs:

The SBT compiler interface is the communication link between SBT and the Scala compiler. It is used to get information from the Scala compiler, and must therefore be compiled against the Scala version in use for the configured projects.

Therefore, if you’re using Scala version 2.12.2 in an SBT project for the first time — or perhaps with a new version of SBT — the SBT compiler interface for Scala 2.12.2 must be compiled on this first run.

This compilation process take a little time, but as that description implies, the compiler interface should only be compiled once for any combination of versions for Scala and SBT, such as Scala 2.12.2 and SBT 0.13.15.