inThisBuild.scala

$ scala
Welcome to Scala 2.12.4 (OpenJDK 64-Bit Server VM, Java 1.8.0_121).
Type in expressions for evaluation. Or try :help.

scala> :paste
// Entering paste mode (ctrl-D to finish)

case class Setting[T](
  key: String,
  value: T
)

object ProjectExtra {
  def inThisBuild(ss: Seq[Setting[_]]): Seq[Setting[_]] = ss
  def inThisBuild[T](ts: T*)(implicit ev: T <:< Setting[_]): Seq[Setting[_]] = ts.map(ev.apply)
}


// Exiting paste mode, now interpreting.

defined class Setting
defined object ProjectExtra

scala> ProjectExtra.inThisBuild(List(Setting("foo", 3), Setting("bar", "bar")))
res0: Seq[Setting[_]] = List(Setting(foo,3), Setting(bar,bar))

scala> ProjectExtra.inThisBuild(Setting("foo", 3), Setting("bar", "bar"))
res1: Seq[Setting[_]] = ArrayBuffer(Setting(foo,3), Setting(bar,bar))