Make autoCompilerPlugins support compiler plugins defined in a internal dependency

requires the compiler plugin project to define exportJars := true

main/src/main/scala/sbt/Defaults.scala

@@ -1329,16 +1329,24 @@ object Classpaths
 		(base * (filter -- excl) +++ (base / config.name).descendantsExcept(filter, excl)).classpath
 
 
-	def autoPlugins(report: UpdateReport): Seq[String] =
+	@deprecated("Specify the classpath that includes internal dependencies", "0.13.0")
+	def autoPlugins(report: UpdateReport): Seq[String] = autoPlugins(report, Nil)
+	def autoPlugins(report: UpdateReport, internalPluginClasspath: Seq[File]): Seq[String] =
 	{
-		val pluginClasspath = report matching configurationFilter(CompilerPlugin.name)
-		classpath.ClasspathUtilities.compilerPlugins(pluginClasspath).map("-Xplugin:" + _.getAbsolutePath).toSeq
+		val pluginClasspath = report.matching(configurationFilter(CompilerPlugin.name)) ++ internalPluginClasspath
+		val plugins = classpath.ClasspathUtilities.compilerPlugins(pluginClasspath)
+		plugins.map("-Xplugin:" + _.getAbsolutePath).toSeq
 	}
 
+	private[this] lazy val internalCompilerPluginClasspath: Initialize[Task[Classpath]] = 
+		(thisProjectRef, settingsData, buildDependencies) flatMap { (ref, data, deps) =>
+			internalDependencies0(ref, CompilerPlugin, CompilerPlugin, data, deps)
+		}
+
 	lazy val compilerPluginConfig = Seq(
 		scalacOptions := {
 			val options = scalacOptions.value
-			if(autoCompilerPlugins.value) options ++ autoPlugins(update.value) else options
+			if(autoCompilerPlugins.value) options ++ autoPlugins(update.value, internalCompilerPluginClasspath.value.files) else options
 		}
 	)
 	@deprecated("Doesn't properly handle non-standard Scala organizations.", "0.13.0")

sbt/src/sbt-test/compiler-project/src-dep-plugin/build.sbt

@@ -0,0 +1,5 @@
+import Configurations.{CompilerPlugin => CPlugin}
+
+lazy val use = project.dependsOn(file("def") % CPlugin).settings(
+	autoCompilerPlugins := true
+)

sbt/src/sbt-test/compiler-project/src-dep-plugin/changes/DemoPlugin.scala

@@ -0,0 +1,10 @@
+package demo
+
+	import scala.tools.nsc.{Global, plugins}
+
+class DemoPlugin(val global: Global) extends plugins.Plugin
+{
+	val name = "demo-plugin"
+	val description = "Throws an error"
+	val components = error("The plugin was successfully registered.")
+}

sbt/src/sbt-test/compiler-project/src-dep-plugin/changes/scalac-plugin.xml

@@ -0,0 +1,4 @@
+<plugin>
+	<name>demo</name>
+	<classname>demo.DemoPlugin</classname>
+</plugin>

sbt/src/sbt-test/compiler-project/src-dep-plugin/def/build.sbt

@@ -0,0 +1,9 @@
+organization := "org.example"
+
+name := "demo-compiler-plugin"
+
+version := "0.1"
+
+libraryDependencies += "org.scala-lang" % "scala-compiler" % scalaVersion.value % "provided"
+
+exportJars := true

sbt/src/sbt-test/compiler-project/src-dep-plugin/test

@@ -0,0 +1,10 @@
+# compilation should succeed on the trivial source file in use/
+> use/compile
+
+# add the plugin
+$ copy-file changes/scalac-plugin.xml def/src/main/resources/scalac-plugin.xml
+$ copy-file changes/DemoPlugin.scala def/DemoPlugin.scala
+
+# if the plugin is successfully registered it will generate an error on construction
+> use/clean
+-> use/compile

sbt/src/sbt-test/compiler-project/src-dep-plugin/use/A.scala

@@ -0,0 +1 @@
+object A

src/sphinx/Community/ChangeSummary_0.13.0.rst

@@ -44,6 +44,7 @@ Improvements
 - Tasks that need a directory for storing cache information can now use the ``cacheDirectory`` method on ``streams``.  This supersedes the ``cacheDirectory`` setting.
 - The environment variables used when forking ``run`` and ``test`` may be set via ``envVars``, which is a ``Task[Map[String,String]]``. (gh-665)
 - Restore class files after an unsuccessful compilation.  This is useful when an error occurs in a later incremental step that requires a fix in the originally changed files.
+- ``autoCompilerPlugins`` now supports compiler plugins defined in a internal dependency.  The plugin project must define ``exportJars := true``.  Depend on the plugin with ``...dependsOn(... % Configurations.CompilerPlugin)``.
 
 Other
 -----