Fix addSbtPlugin to use the correct version of sbt

Fixes #3393

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

@@ -2956,7 +2956,7 @@ trait BuildExtra extends BuildCommon with DefExtra {
    */
   def addSbtPlugin(dependency: ModuleID): Setting[Seq[ModuleID]] =
     libraryDependencies += {
-      val sbtV = (sbtBinaryVersion in update).value
+      val sbtV = (sbtBinaryVersion in pluginCrossBuild).value
       val scalaV = (scalaBinaryVersion in update).value
       sbtPluginExtra(dependency, sbtV, scalaV)
     }

notes/0.13.17/addSbtPlugin-cross.markdown

@@ -0,0 +1,7 @@
+### Bug fixes
+
+- Fixes `addSbtPlugin` to use the correct version of sbt. [#3393][]/[#3397][] by [@dwijnand][]
+
+  [#3393]: https://github.com/sbt/sbt/issues/3393
+  [#3397]: https://github.com/sbt/sbt/pull/3397
+  [@dwijnand]: http://github.com/dwijnand

sbt/src/sbt-test/project/cross-plugins-defaults/build.sbt

@@ -4,6 +4,8 @@ val buildCrossList = List("2.10.6", "2.11.11", "2.12.2")
 scalaVersion in ThisBuild := "2.12.2"
 crossScalaVersions in ThisBuild := buildCrossList
 
+addSbtPlugin("com.eed3si9n" % "sbt-buildinfo" % "0.7.0")
+
 lazy val root = (project in file("."))
   .settings(
     sbtPlugin := true,
@@ -16,12 +18,21 @@ lazy val app = (project in file("app"))
 
 def mkCheck(scalaBinV: String, sbtBinVer: String) = Def task {
   val crossV = (sbtVersion in pluginCrossBuild).value
+  val crossBinV = (sbtBinaryVersion in pluginCrossBuild).value
   val sv = projectID.value.extraAttributes("e:scalaVersion")
   assert(sbtVersion.value startsWith baseSbt, s"Wrong sbt version: ${sbtVersion.value}")
   assert(sv == scalaBinV, s"Wrong e:scalaVersion: $sv")
   assert(scalaBinaryVersion.value == scalaBinV, s"Wrong Scala binary version: ${scalaBinaryVersion.value}")
   assert(crossV startsWith sbtBinVer, s"Wrong `sbtVersion in pluginCrossBuild`: $crossV")
 
+  val ur = update.value
+  val cr = ur.configuration(Compile).get
+  val mr = cr.modules.find(mr => mr.module.organization == "com.eed3si9n" && mr.module.name == "sbt-buildinfo").get
+  val plugSv = mr.module.extraAttributes("scalaVersion")
+  val plugSbtV = mr.module.extraAttributes("sbtVersion")
+  assert(plugSv == scalaBinV, s"Wrong plugin scalaVersion: $plugSv")
+  assert(plugSbtV == sbtBinVer, s"Wrong plugin scalaVersion: $sbtBinVer")
+
   // crossScalaVersions in app should not be affected, per se or after ^^
   val appCrossScalaVersions = (crossScalaVersions in app).value.toList
   val appScalaVersion = (scalaVersion in app).value