Redefine crossScalaVersions, because it's Def.derive..

Fixes #3495

main/src/main/scala/sbt/Cross.scala

@@ -94,7 +94,7 @@ object Cross {
     (currentRef :: currentProject.aggregate.toList.flatMap(findAggregates)).distinct
   }
 
-  private def crossVersions(extracted: Extracted, proj: ProjectRef): Seq[String] = {
+  private def crossVersions(extracted: Extracted, proj: ResolvedReference): Seq[String] = {
     import extracted._
     (crossScalaVersions in proj get structure.data) getOrElse {
       // reading scalaVersion is a one-time deal
@@ -274,12 +274,14 @@ object Cross {
       excluded.foreach(logProject.tupled)
     }
 
-    val projects: Seq[ResolvedReference] = {
+    val projects: Seq[(ResolvedReference, Seq[ScalaVersion])] = {
       val projectScalaVersions =
         structure.allProjectRefs.map(proj => proj -> crossVersions(extracted, proj))
       if (switch.version.force) {
         logSwitchInfo(projectScalaVersions, Nil)
-        structure.allProjectRefs ++ structure.units.keys.map(BuildRef.apply)
+        projectScalaVersions ++ structure.units.keys
+          .map(BuildRef.apply)
+          .map(proj => proj -> crossVersions(extracted, proj))
       } else {
         val binaryVersion = CrossVersion.binaryScalaVersion(version)
 
@@ -288,7 +290,7 @@ object Cross {
             scalaVersions.exists(v => CrossVersion.binaryScalaVersion(v) == binaryVersion)
         }
         logSwitchInfo(included, excluded)
-        included.map(_._1)
+        included
       }
     }
 
@@ -298,36 +300,41 @@ object Cross {
   private def setScalaVersionForProjects(
       version: String,
       instance: Option[(File, ScalaInstance)],
-      projects: Seq[Reference],
+      projects: Seq[(ResolvedReference, Seq[String])],
       state: State,
       extracted: Extracted
   ): State = {
     import extracted._
 
-    val newSettings = projects.flatMap { project =>
-      val scope = Scope(Select(project), Zero, Zero, Zero)
+    val newSettings = projects.flatMap {
+      case (project, scalaVersions) =>
+        val scope = Scope(Select(project), Zero, Zero, Zero)
 
-      instance match {
-        case Some((home, inst)) =>
-          Seq(
-            scalaVersion in scope := version,
-            scalaHome in scope := Some(home),
-            scalaInstance in scope := inst
-          )
-        case None =>
-          Seq(
-            scalaVersion in scope := version,
-            scalaHome in scope := None
-          )
-      }
+        instance match {
+          case Some((home, inst)) =>
+            Seq(
+              scalaVersion in scope := version,
+              crossScalaVersions in scope := scalaVersions,
+              scalaHome in scope := Some(home),
+              scalaInstance in scope := inst
+            )
+          case None =>
+            Seq(
+              scalaVersion in scope := version,
+              crossScalaVersions in scope := scalaVersions,
+              scalaHome in scope := None
+            )
+        }
     }
 
     val filterKeys: Set[AttributeKey[_]] = Set(scalaVersion, scalaHome, scalaInstance).map(_.key)
 
+    val projectsContains: Reference => Boolean = projects.map(_._1).toSet.contains
+
     // Filter out any old scala version settings that were added, this is just for hygiene.
     val filteredRawAppend = session.rawAppend.filter(_.key match {
       case ScopedKey(Scope(Select(ref), Zero, Zero, Zero), key)
-          if filterKeys.contains(key) && projects.contains(ref) =>
+          if filterKeys.contains(key) && projectsContains(ref) =>
         false
       case _ => true
     })

notes/1.0.2/plusplus-not-changing-crossScalaVersions.md

@@ -0,0 +1,12 @@
+[@dwijnand]: https://github.com/dwijnand
+
+[#3495]: https://github.com/sbt/sbt/issues/3495
+[#3526]: https://github.com/sbt/sbt/pull/3526
+
+### Fixes with compatibility implications
+
+### Improvements
+
+### Bug fixes
+
+- Fixes `++` so it don't change the value of `crossScalaVersion`. [#3495][]/[#3526][] by [@dwijnand][]

sbt/src/sbt-test/actions/cross-multiproject/build.sbt

@@ -1,3 +1,6 @@
+inThisBuild(List(
+  crossScalaVersions := Seq("2.12.1", "2.11.8")
+))
 
 lazy val rootProj = (project in file("."))
   .aggregate(libProj, fooPlugin)
@@ -20,4 +23,9 @@ lazy val fooPlugin = (project in file("sbt-foo"))
     crossScalaVersions := Seq("2.12.1")
   )
 
+lazy val extrasProj = (project in file("extras"))
+  .settings(
+    name := "foo-extras",
+  )
+
 addCommandAlias("build", "compile")

sbt/src/sbt-test/actions/cross-multiproject/test

@@ -46,3 +46,10 @@ $ exists lib/target/scala-2.12
 -$ exists lib/target/scala-2.11
 $ exists sbt-foo/target/scala-2.12
 -$ exists sbt-foo/target/scala-2.11
+
+> clean
+# Test ++ leaves crossScalaVersions unchanged
+> ++2.12.1
+> +extrasProj/compile
+$ exists extras/target/scala-2.11
+$ exists extras/target/scala-2.12