Merge pull request #1467 from sbt/wip/eviction-warning

Eviction warnings (Fixes #1200)

util/collection/src/main/scala/sbt/ShowLines.scala

@@ -0,0 +1,15 @@
+package sbt
+
+trait ShowLines[A] {
+  def showLines(a: A): Seq[String]
+}
+object ShowLines {
+  def apply[A](f: A => Seq[String]): ShowLines[A] =
+    new ShowLines[A] {
+      def showLines(a: A): Seq[String] = f(a)
+    }
+
+  implicit class ShowLinesOp[A: ShowLines](a: A) {
+    def lines: Seq[String] = implicitly[ShowLines[A]].showLines(a)
+  }
+}