Reproduce Twirl regression

Ref #4681

sbt/src/sbt-test/plugins/twirl/build.sbt

@@ -0,0 +1,12 @@
+
+lazy val check = taskKey[Unit]("")
+
+lazy val root = (project in file("."))
+  .enablePlugins(TwirlPlugin)
+  .settings(
+    check := {
+      val templates = (Compile / twirlCompileTemplates / sources).value
+      assert(templates.nonEmpty)
+      assert(!templates.exists(_.toString.contains("hidden")))
+    }
+  )

sbt/src/sbt-test/plugins/twirl/project/TwirlPlugin.scala

@@ -0,0 +1,29 @@
+import sbt._
+import Keys._
+
+object TwirlPlugin extends AutoPlugin {
+  override def requires = sbt.plugins.JvmPlugin
+  override def trigger = noTrigger
+
+  object autoImport {
+    val twirlCompileTemplates = taskKey[Seq[File]]("Compile twirl templates into scala source files")
+  }
+
+  override def projectSettings: Seq[Setting[_]] =
+    inConfig(Compile)(twirlSettings) ++
+        inConfig(Test)(twirlSettings)
+
+  import autoImport._
+
+  def twirlSettings: Seq[Setting[_]] =  Seq(
+    twirlCompileTemplates / includeFilter := "*.scala.*",
+    twirlCompileTemplates / excludeFilter := HiddenFileFilter,
+    twirlCompileTemplates / sourceDirectories := Seq(sourceDirectory.value / "twirl"),
+
+    twirlCompileTemplates / sources := Defaults.collectFiles(
+      twirlCompileTemplates / sourceDirectories,
+      twirlCompileTemplates / includeFilter,
+      twirlCompileTemplates / excludeFilter
+    ).value
+  )
+}

sbt/src/sbt-test/plugins/twirl/src/main/twirl/play/routes/forwardsRouter.scala.twirl

@@ -0,0 +1,3 @@
+@import play.routes.compiler._
+@import play.routes.compiler.templates._
+@import InjectedRoutesGenerator.Dependency

sbt/src/sbt-test/plugins/twirl/test

@@ -0,0 +1 @@
+> check