Merge pull request #1992 from dwijnand/cross-scala-versions-default

Fix crossScalaVersions default, derived from scalaVersion. Fixes #1828.

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

@@ -239,7 +239,7 @@ object Defaults extends BuildCommon {
     javacOptions :== Nil,
     scalacOptions :== Nil,
     scalaVersion := appConfiguration.value.provider.scalaProvider.version,
-    crossScalaVersions := Seq(scalaVersion.value),
+    derive(crossScalaVersions := Seq(scalaVersion.value)),
     derive(compilersSetting),
     derive(scalaBinaryVersion := binaryScalaVersion(scalaVersion.value))
   ))

notes/0.13.9/cross-scala-versions-default.markdown

@@ -0,0 +1,24 @@
+
+  [@dwijnand]: http://github.com/dwijnand
+  [1828]: https://github.com/sbt/sbt/issues/1828
+  [1992]: https://github.com/sbt/sbt/pull/1992
+
+### Fixes with compatibility implications
+
+- Starting 0.13.9, `crossScalaVersions` default value is fixed back to the older 0.12.x behavior. See below for
+  details
+
+### Improvements
+
+### Bug fixes
+
+### `crossScalaVersions` default value
+
+As of this fix `crossScalaVersions` returns to the behaviour present in `0.12.4` whereby it defaults to what
+`scalaVersion` is set to, for example if `scalaVersion` is set to `"2.11.6"`, `crossScalaVersions` now defaults
+to `Seq("2.11.6")`.
+
+Therefore when upgrading from any version between `0.13.0` and `0.13.8` be aware of this new default if
+your build setup depended on it.
+
+[#1828][1828]/[#1992][1992] by [@dwijnand][@dwijnand]

sbt/src/sbt-test/project/cross-scala-versions-default/build.sbt

@@ -0,0 +1,6 @@
+scalaVersion := "2.11.6"
+
+TaskKey[Unit]("check") := {
+  assert(crossScalaVersions.value == Seq("2.11.6"),
+    s"""crossScalaVersions should be Seq("2.11.6") but is ${crossScalaVersions.value}""")
+}

sbt/src/sbt-test/project/cross-scala-versions-default/test

@@ -0,0 +1 @@
+> check