add testing or at least a demo to this repo

[SethTisue]

there is advice on this in the “Compiler Plugins 101” slides, but it might as well be in this repo directly, too

@hrhino has suggested using this to test:

scalacOptions in Test ++= Seq(
  s"-Xplugin:${(packageBin in Compile).value}",
  s"-Jdummy=${System.currentTimeMillis()}",
)

the -Jdummy thing is an attempt to fool sbt into rebuilding when necessary; it's copied (perhaps cargo-culted) from scala-continuations; I should see whether it is necessary on modern sbt, whether it actually works, and whether there's a better, less kludgey way

[SethTisue]

I have found by experiment that it is in fact necessary to do something so that changing the plugin causes code in src/test to be rebuilt

[SethTisue]

maybe the best thing is actually to put the test code in a separate subproject, rather than try to subvert sbt's usual expectations

[SethTisue]

I tried the subproject thing:

val commonSettings = Seq(
  organization := "com.lightbend",
  version := "0.0.1",
  crossScalaVersions := Seq("2.12.6", "2.13.0-M4"),
  scalaVersion := crossScalaVersions.value.head,
  crossVersion := CrossVersion.patch,
  scalacOptions ++= Seq(
    "-encoding", "utf-8",
    "-deprecation",
    "-unchecked",
    "-feature",
    "-Xlint",
    "-Xfatal-warnings",
    "-Ywarn-value-discard"
  ))

lazy val plugin =
  project.in(file("plugin"))
    .settings(commonSettings)
    .settings(
      name := "cloc-plugin",
      libraryDependencies +=
        "org.scala-lang" % "scala-compiler" % scalaVersion.value % "provided"
    )

lazy val tests =
  project.in(file("tests"))
    .settings(commonSettings)
    .settings(
      scalacOptions ++= Seq(
        s"-Xplugin:${(plugin / Compile / packageBin).value}",
        s"-Xplugin-require:cloc"
      ))
    .dependsOn(plugin)

but it didn't help

[SethTisue]

I see kind-projector does

scalacOptions in Test ++= {
  val jar = (packageBin in Compile).value
  Seq(s"-Xplugin:${jar.getAbsolutePath}", s"-Jdummy=${jar.lastModified}") // ensures recompile
}

and so does better-monadic-for