suppressing the warning but not the error

In this code https://github.com/scalaz/ioeffect/blob/6f57538969e38f62f942a05d0b7734483629dc62/src/main/scala/scalaz/ioeffect/Void.scala#L34-L35

we are able to suppress this warning

[error] src/main/scala/scalaz/ioeffect/Void.scala:33:26: dead code following this construct
[error] private[ioeffect] object VoidImpl extends VoidModule with VoidSyntax {
[error]                          ^

but when scalacOptions in Compile += "-Xfatal-warnings" is added, we get

[info] Compiling 13 Scala sources to /tmp/fommil-sbt/home/fommil/Projects/scalaz-ioeffect/target/scala-2.12/classes ...
[error] No warnings can be incurred under -Xfatal-warnings.
[error] one error found

[fommil]

I think it would be good if all plugins tried to be good citizens to the best of their ability, with silencer at the end of the list as the nuclear option.

[ghik]

OK, I think I nailed it.

There is a clash between silencer and semanticdb compiler plugin. Both have their own error/warning reporter which wraps the original reporter. They should totally be able to wrap each other and work together just fine but it’s important to ensure that the silencer reporter wraps the semanticdb reporter and not the other way. This means that silencer plugin must be applied after semanticdb plugin, which can be forced using this workaround:

def ensureSilencerIsLast(options: Seq[String]): Seq[String] = {
  val (Seq(silencer), rest) = options.partition(o => o.startsWith("-Xplugin:") && o.contains("silencer"))
  rest :+ silencer
}

scalacOptions in Compile := ensureSilencerIsLast((scalacOptions in Compile).value)
scalacOptions in Test := ensureSilencerIsLast((scalacOptions in Test).value)