Implemented clean task + added integration test. Fixes #685

sbt-coursier/src/main/scala/coursier/CoursierPlugin.scala

@@ -9,7 +9,7 @@ object CoursierPlugin extends AutoPlugin {
 
   override def trigger = allRequirements
 
-  override def requires = sbt.plugins.IvyPlugin
+  override def requires = sbt.plugins.JvmPlugin
 
   object autoImport {
     val coursierParallelDownloads = Keys.coursierParallelDownloads
@@ -153,6 +153,11 @@ object CoursierPlugin extends AutoPlugin {
     shadedConfigOpt: Option[(String, String)],
     packageConfigs: Seq[(Configuration, String)]
   ) = hackHack ++ Seq(
+    clean := {
+      clean.value
+      Tasks.resolutionsCache.clear()
+      Tasks.reportsCache.clear()
+    },
     coursierResolvers := Tasks.coursierResolversTask.value,
     coursierRecursiveResolvers := Tasks.coursierRecursiveResolversTask.value,
     coursierSbtResolvers := {

sbt-coursier/src/main/scala/coursier/Tasks.scala

@@ -398,7 +398,7 @@ object Tasks {
     }
   }
 
-  private final case class ResolutionCacheKey(
+  private[coursier] final case class ResolutionCacheKey(
     project: Project,
     repositories: Seq[Repository],
     userEnabledProfiles: Set[String],
@@ -406,7 +406,7 @@ object Tasks {
     sbtClassifiers: Boolean
   )
 
-  private final case class ReportCacheKey(
+  private[coursier] final case class ReportCacheKey(
     project: Project,
     resolution: Map[Set[String], Resolution],
     withClassifiers: Boolean,
@@ -414,10 +414,10 @@ object Tasks {
     ignoreArtifactErrors: Boolean
   )
 
-  private val resolutionsCache = new mutable.HashMap[ResolutionCacheKey, Map[Set[String], Resolution]]
+  private[coursier] val resolutionsCache = new mutable.HashMap[ResolutionCacheKey, Map[Set[String], Resolution]]
   // these may actually not need to be cached any more, now that the resolutions
   // are cached
-  private val reportsCache = new mutable.HashMap[ReportCacheKey, UpdateReport]
+  private[coursier] val reportsCache = new mutable.HashMap[ReportCacheKey, UpdateReport]
 
   private def forcedScalaModules(
     scalaOrganization: String,

sbt-coursier/src/sbt-test/sbt-coursier/clean/build.sbt

@@ -0,0 +1,13 @@
+scalaVersion := "2.11.8"
+
+val checkEmpty = TaskKey[Unit]("checkEmpty")
+
+checkEmpty := {
+  assert(coursier.Helper.checkEmpty)
+}
+
+val checkNotEmpty = TaskKey[Unit]("checkNotEmpty")
+
+checkNotEmpty := {
+  assert(!coursier.Helper.checkEmpty)
+}

sbt-coursier/src/sbt-test/sbt-coursier/clean/project/helper.scala

@@ -0,0 +1,9 @@
+package coursier
+
+object Helper {
+
+  def checkEmpty(): Boolean = {
+    Tasks.resolutionsCache.isEmpty && Tasks.reportsCache.isEmpty
+  }
+
+}

sbt-coursier/src/sbt-test/sbt-coursier/clean/project/plugins.sbt

@@ -0,0 +1,11 @@
+{
+  val pluginVersion = sys.props.getOrElse(
+    "plugin.version",
+    throw new RuntimeException(
+      """|The system property 'plugin.version' is not defined.
+         |Specify this property using the scriptedLaunchOpts -D.""".stripMargin
+    )
+  )
+
+  addSbtPlugin("io.get-coursier" % "sbt-coursier" % pluginVersion)
+}

sbt-coursier/src/sbt-test/sbt-coursier/clean/test

@@ -0,0 +1,5 @@
+> checkEmpty
+> update
+> checkNotEmpty
+> clean
+> checkEmpty