Make plugin a State => State too (#2)

To load it via the apply command of sbt, like sbt-structure does.

sbt-cs-publish/src/main/scala/sbtcspublish/ApplyState.scala

@@ -0,0 +1,37 @@
+package sbtcspublish
+
+import java.net.URI
+
+import sbt.internal.SessionSettings
+import sbt.{BuiltinCommands, GlobalScope, Project, Reference, Scope, Select, Setting, State, Zero}
+
+trait ApplyState extends (State => State) {
+
+  def projectSettings: Seq[Setting[_]]
+  def globalSettings: Seq[Setting[_]]
+
+
+  // from https://github.com/JetBrains/sbt-structure/blob/16574c8d17afcc99de9aa6d73ac0e5349c9a32a4/extractor/src/main/scala-sbt-0.13-1.0/org/jetbrains/sbt/CreateTasks.scala
+
+  def apply(state: State): State =
+    applySettings(state, globalSettings, projectSettings)
+
+  private def applySettings(state: State, globalSettings: Seq[Setting[_]], projectSettings: Seq[Setting[_]]): State = {
+    val extracted = Project.extract(state)
+    import extracted.{structure => extractedStructure, _}
+    val transformedGlobalSettings = Project.transform(_ => GlobalScope, globalSettings)
+    val transformedProjectSettings = extractedStructure.allProjectRefs.flatMap { projectRef =>
+      transformSettings(projectScope(projectRef), projectRef.build, rootProject, projectSettings)
+    }
+    reapply(extracted.session.appendRaw(transformedGlobalSettings ++ transformedProjectSettings), state)
+  }
+
+  private def transformSettings(thisScope: Scope, uri: URI, rootProject: URI => String, settings: Seq[Setting[_]]): Seq[Setting[_]] =
+    Project.transform(Scope.resolveScope(thisScope, uri, rootProject), settings)
+
+  private def reapply(session: SessionSettings, s: State): State =
+    BuiltinCommands.reapply(session, Project.structure(s), s)
+
+  private def projectScope(project: Reference): Scope = Scope(Select(project), Zero, Zero, Zero)
+
+}

sbt-cs-publish/src/main/scala/sbtcspublish/SbtCsPublishPlugin.scala

@@ -8,7 +8,7 @@ import sbt.complete.DefaultParsers._
 import sbt.Keys.{baseDirectory, ivyPaths, makeIvyXml, packagedArtifacts, projectID, scalaModuleInfo}
 import sbt.librarymanagement.{Artifact, CrossVersion}
 
-object SbtCsPublishPlugin extends AutoPlugin {
+object SbtCsPublishPlugin extends AutoPlugin with ApplyState {
 
   object autoImport {
     val csPublishLocal = taskKey[Unit]("")