Add SbtPlugin

Fixes #3538

This brings in `sbt.ScriptedPlugin` as `sbt.plugins.ScriptedPlugin` into sbt mothership.
In addition, `sbt.plugins.SbtPlugin` is added that enables the scripted plugin and `sbtPlugin := true`.

This allows plugin authors to bring in scripted plugin by writing:

```scala
lazy val root = (project in file("."))
  .enablePlugins(SbtPlugin)
```

build.sbt

@@ -272,11 +272,18 @@ lazy val scriptedSbtProj = (project in scriptedPath / "sbt")
   .configure(addSbtIO, addSbtUtilLogging, addSbtCompilerInterface, addSbtUtilScripted, addSbtLmCore)
 
 lazy val scriptedPluginProj = (project in scriptedPath / "plugin")
-  .dependsOn(sbtProj)
+  .dependsOn(mainProj)
   .settings(
     baseSettings,
     name := "Scripted Plugin",
     mimaSettings,
+    mimaBinaryIssueFilters ++= Seq(
+      // scripted plugin has moved into sbt mothership as sbt.plugins.ScriptedPlugin.
+      // sbt.ScriptedPlugin is still here for bincomat.
+      exclude[DirectMissingMethodProblem]("sbt.ScriptedPlugin#autoImport*"),
+      exclude[IncompatibleResultTypeProblem]("sbt.ScriptedPlugin.requires"),
+      exclude[DirectMissingMethodProblem]("sbt.ScriptedPlugin.scriptedParser"),
+    ),
   )
   .configure(addSbtCompilerClasspath)
 
@@ -417,7 +424,7 @@ lazy val mainSettingsProj = (project in file("main-settings"))
 // The main integration project for sbt.  It brings all of the projects together, configures them, and provides for overriding conventions.
 lazy val mainProj = (project in file("main"))
   .enablePlugins(ContrabandPlugin)
-  .dependsOn(logicProj, actionsProj, mainSettingsProj, runProj, commandProj, collectionProj)
+  .dependsOn(logicProj, actionsProj, mainSettingsProj, runProj, commandProj, collectionProj, scriptedSbtProj)
   .settings(
     testedBaseSettings,
     name := "Main",

main/src/main/scala/sbt/internal/PluginDiscovery.scala

@@ -47,6 +47,8 @@ object PluginDiscovery {
       "sbt.plugins.IvyPlugin" -> sbt.plugins.IvyPlugin,
       "sbt.plugins.JvmPlugin" -> sbt.plugins.JvmPlugin,
       "sbt.plugins.CorePlugin" -> sbt.plugins.CorePlugin,
+      "sbt.plugins.ScriptedPlugin" -> sbt.plugins.ScriptedPlugin,
+      "sbt.plugins.SbtPlugin" -> sbt.plugins.SbtPlugin,
       "sbt.plugins.JUnitXmlReportPlugin" -> sbt.plugins.JUnitXmlReportPlugin,
       "sbt.plugins.Giter8TemplatePlugin" -> sbt.plugins.Giter8TemplatePlugin
     )

main/src/main/scala/sbt/plugins/SbtPlugin.scala

@@ -0,0 +1,19 @@
+/*
+ * sbt
+ * Copyright 2011 - 2017, Lightbend, Inc.
+ * Copyright 2008 - 2010, Mark Harrah
+ * Licensed under BSD-3-Clause license (see LICENSE)
+ */
+
+package sbt
+package plugins
+
+import Keys._
+
+object SbtPlugin extends AutoPlugin {
+  override def requires = ScriptedPlugin
+
+  override lazy val projectSettings = Seq(
+    sbtPlugin := true
+  )
+}

main/src/main/scala/sbt/plugins/ScriptedPlugin.scala

@@ -6,13 +6,21 @@
  */
 
 package sbt
+package plugins
 
+import java.io.File
 import Def.Initialize
 import Keys._
 import sbt.internal.util.complete.{ Parser, DefaultParsers }
 import sbt.internal.inc.classpath.ClasspathUtilities
 import sbt.internal.inc.ModuleUtilities
 import java.lang.reflect.Method
+import sbt.librarymanagement._
+import sbt.librarymanagement.syntax._
+import sbt.io._
+import sbt.io.syntax._
+import Project._
+import Def._
 
 object ScriptedPlugin extends AutoPlugin {
   override def requires = plugins.JvmPlugin
@@ -38,6 +46,7 @@ object ScriptedPlugin extends AutoPlugin {
     val scriptedDependencies = TaskKey[Unit]("scripted-dependencies")
     val scripted = InputKey[Unit]("scripted")
   }
+
   import autoImport._
   override lazy val projectSettings = Seq(
     ivyConfigurations ++= Seq(ScriptedConf, ScriptedLaunchConf),
@@ -66,7 +75,7 @@ object ScriptedPlugin extends AutoPlugin {
     scriptedRun := scriptedRunTask.value,
     scriptedDependencies := {
       def use[A](@deprecated("unused", "") x: A*): Unit = () // avoid unused warnings
-      val analysis = (compile in Test).value
+      val analysis = (Keys.compile in Test).value
       val pub = (publishLocal).value
       use(analysis, pub)
     },
@@ -143,7 +152,6 @@ object ScriptedPlugin extends AutoPlugin {
     //(token(Space) ~> matched(testID)).*
     (token(Space) ~> (PagedIds | testIdAsGroup)).* map (_.flatten)
   }
-
   def scriptedTask: Initialize[InputTask[Unit]] = Def.inputTask {
     val args = scriptedParser(sbtTestDirectory.value).parsed
     scriptedDependencies.value
@@ -164,6 +172,6 @@ object ScriptedPlugin extends AutoPlugin {
   }
 
   private[this] def getJars(config: Configuration): Initialize[Task[PathFinder]] = Def.task {
-    PathFinder(Classpaths.managedJars(config, classpathTypes.value, update.value).map(_.data))
+    PathFinder(Classpaths.managedJars(config, classpathTypes.value, Keys.update.value).map(_.data))
   }
 }

sbt/src/sbt-test/project/scripted-plugin/build.sbt

@@ -0,0 +1,2 @@
+lazy val root = (project in file("."))
+  .enablePlugins(SbtPlugin)