例えば 2.12 と 2.13 のクロスコンパイルする場合に、
2.12 だけ -Xfatal-warnings をつけたい場合。
crossScalaVersions := Seq("2.12.10", "2.13.1")
:
scalacOptions in Compile ++= Seq(
"-feature",
"-deprecation",
"-unchecked",
"-Xlint:",
"-Xlint:-missing-interpolator",
"-Yno-adapted-args",
"-Ywarn-dead-code",
"-Ywarn-numeric-widen",
"-language:implicitConversions"
) ++ PartialFunction.condOpt(CrossVersion.partialVersion(scalaVersion.value)) {
case Some((2, v)) if v <= 12 => "-Xfatal-warnings"
}.toSeqのような感じにする。