Add test for command crossing using !

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

@@ -0,0 +1,32 @@
+lazy val compile2 = taskKey[Unit]("")
+
+lazy val root = (project in file("."))
+  .aggregate(foo, bar, client)
+  .settings(
+    crossScalaVersions := Nil,
+    addCommandAlias("build", "compile2"),
+  )
+
+lazy val foo = project
+  .settings(
+    crossScalaVersions := Seq("2.12.11", "2.13.1"),
+    libraryDependencies += "org.scalatest" %% "scalatest" % "3.1.0",
+    compile2 := {
+      // This tests that +build will ignore bar's crossScalaVersions and use root's like sbt 0.13
+      val x = (LocalProject("bar") / scalaVersion).value
+      assert(x == scalaVersion.value, s"$x == ${scalaVersion.value}")
+      (Compile / compile).value
+    },
+  )
+
+lazy val bar = project
+  .settings(
+    crossScalaVersions := Seq("2.12.11"),
+    compile2 := (Compile / compile).value,
+  )
+
+lazy val client = project
+  .settings(
+    crossScalaVersions := Seq("2.12.11", "2.13.1"),
+    compile2 := (Compile / compile).value,
+  )

sbt/src/sbt-test/actions/cross-advanced/test

@@ -0,0 +1,17 @@
+> + clean
+
+## test input task
+> + foo / testOnly foo.FooSpec
+> + testOnly foo.FooSpec
+
+## test + with command or alias
+> clean
+## for command cross building you do need crossScalaVerions on root
+> set root/crossScalaVersions := Seq("2.12.11", "2.13.1")
+> + build
+$ exists foo/target/scala-2.12
+$ exists foo/target/scala-2.13
+$ exists bar/target/scala-2.12
+$ exists bar/target/scala-2.13
+$ exists client/target/scala-2.12
+$ exists client/target/scala-2.13

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

@@ -1,16 +0,0 @@
-lazy val root = (project in file("."))
-  .aggregate(foo, client)
-  .settings(
-    crossScalaVersions := Nil
-  )
-
-lazy val foo = project
-  .settings(
-    crossScalaVersions := Seq("2.12.11", "2.13.1"),
-    libraryDependencies += "org.scalatest" %% "scalatest" % "3.1.0",
-  )
-
-lazy val client = project
-  .settings(
-    crossScalaVersions := Seq("2.12.11", "2.13.1"),
-  )

sbt/src/sbt-test/actions/cross-test-only/test

@@ -1,5 +0,0 @@
-> + clean
-
-> + foo / testOnly foo.FooSpec
-
-> + testOnly foo.FooSpec