The setup of the scalafix module roughly follows the example in https://github.com/scalacenter/scalafix.g8.

Adding new rules

• Add before/after test file in scalafix-test-input / scalafix-test-output
• Add rule in scalafix-rules
• run test in akka-http-scalafix-tests

Applying locally defined rules to docs examples

• run scalafixEnable on the sbt shell (this will unfortunately require a complete rebuild afterwards)
• run set scalacOptions in ThisBuild += "-P:semanticdb:synthetics:on" to allow access to synthetics
• e.g. run docs/scalafixAll MigrateToServerBuilder

Note: There's some weird stuff going on regarding cross-publishing. The scalafixScalaBinaryVersion line in build.sbt should fix it but if running the rule fails with a weird error, try switching to Scala 2.12 first with ++2.12.11 (or whatever is now the current version).