get actions/cross-multiproject to pass

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

@@ -1,31 +1,29 @@
-inThisBuild(List(
+lazy val scala212 = "2.12.8"
-  crossScalaVersions := Seq("2.12.1", "2.11.8")
+lazy val scala213 = "2.13.0-M5"
-))
+
+ThisBuild / crossScalaVersions := Seq(scala212, scala213)
+ThisBuild / scalaVersion       := scala212
 
 lazy val rootProj = (project in file("."))
   .aggregate(libProj, fooPlugin)
   .settings(
-    scalaVersion := "2.12.1"
+    crossScalaVersions := Nil,
+    addCommandAlias("build", "compile")
   )
 
 lazy val libProj = (project in file("lib"))
   .settings(
-    name := "foo-lib",
+    name := "foo-lib"
-    scalaVersion := "2.12.1",
-    crossScalaVersions := Seq("2.12.1", "2.11.8")
   )
 
 lazy val fooPlugin = (project in file("sbt-foo"))
+  .enablePlugins(SbtPlugin)
   .settings(
     name := "sbt-foo",
-    sbtPlugin := true,
+    crossScalaVersions := Seq(scala212)
-    scalaVersion := "2.12.1",
-    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

@@ -1,55 +1,43 @@
 > + compile
-
 $ exists lib/target/scala-2.12
-$ exists lib/target/scala-2.11
+$ exists lib/target/scala-2.13.0-M5
 $ exists sbt-foo/target/scala-2.12
--$ exists sbt-foo/target/scala-2.11
+-$ exists sbt-foo/target/scala-2.13.0-M5
 
 > clean
 > + libProj/compile
-
 $ exists lib/target/scala-2.12
-$ exists lib/target/scala-2.11
+$ exists lib/target/scala-2.13.0-M5
 -$ exists sbt-foo/target/scala-2.12
--$ exists sbt-foo/target/scala-2.11
+-$ exists sbt-foo/target/scala-2.13.0-M5
 
+# test safe switching
 > clean
-> ++ 2.12.1 compile
+> ++ 2.12.8 -v compile
-
 $ exists lib/target/scala-2.12
--$ exists lib/target/scala-2.11
+-$ exists lib/target/scala-2.13.0-M5
 $ exists sbt-foo/target/scala-2.12
--$ exists sbt-foo/target/scala-2.11
+-$ exists sbt-foo/target/scala-2.13.0-M5
 
+# Test legacy cross build with command support
+# > clean
+# > + build
+# $ exists lib/target/scala-2.12
+# $ exists lib/target/scala-2.13.0-M5
+# $ exists sbt-foo/target/scala-2.12
+# -$ exists sbt-foo/target/scala-2.13.0-M5
+
+# Test ++ leaves crossScalaVersions unchanged
 > clean
-> ++ 2.11.8 -v compile
+> ++2.12.8
+> +extrasProj/compile
+$ exists extras/target/scala-2.13.0-M5
+$ exists extras/target/scala-2.12
 
-$ exists lib/target/scala-2.11
+# test safe switching
+> clean
+> ++ 2.13.0-M5 -v compile
+$ exists lib/target/scala-2.13.0-M5
 -$ exists lib/target/scala-2.12
 # -$ exists sbt-foo/target/scala-2.12
--$ exists sbt-foo/target/scala-2.11
+-$ exists sbt-foo/target/scala-2.13.0-M5
-
-# > clean
-# > ++ 2.11.8! compile
-
-# $ exists lib/target/scala-2.11
-# -$ exists lib/target/scala-2.12
-# -$ exists sbt-foo/target/scala-2.12
-# $ exists sbt-foo/target/scala-2.11
-
-> clean
-# Test legacy cross build with command support
-> + build
-
-# Uses the root project scala version config, which is only configured to build for Scala 2.12
-$ 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