First hack pass at cross-build discovery and command-running now works.

Can be tested out on our `build.sc` via `scalaplugin/target/mill run Core.cross[a].printIt`

Needs tons of cleanup...

2 files changed, 84 insertions, 2 deletions

diff --git a/core/src/test/scala/mill/discover/CrossModuleTests.scala b/core/src/test/scala/mill/discover/CrossModuleTests.scala
new file mode 100644
index 00000000..c4e075da
--- /dev/null
+++ b/core/src/test/scala/mill/discover/CrossModuleTests.scala
@@ -0,0 +1,82 @@
+package mill.discover
+
+import mill.{Module, T}
+import mill.define.Cross
+import utest._
+
+object CrossModuleTests extends TestSuite{
+
+  val tests = Tests{
+
+    'cross - {
+      object outer{
+        val crossed =
+          for(n <- Cross("2.10.6", "2.11.8", "2.12.4"))
+          yield new Module{
+            def scalaVersion = n
+          }
+      }
+
+      val Some((gen, innerMirror)) = Discovered[outer.type]
+        .mirror
+        .children
+        .head._2
+        .asInstanceOf[Mirror[outer.type, outer.crossed.type]]
+        .crossChildren
+
+      val keys = gen(outer.crossed)
+      assert(keys == List(List("2.10.6"), List("2.11.8"), List("2.12.4")))
+      for(k <- keys){
+        assert(outer.crossed(k).scalaVersion == k.head)
+      }
+    }
+    'doubleCross - {
+      object outer{
+        val crossed =
+          for{
+            platform <- Cross("", "sjs0.6", "native0.3")
+            scalaVersion <- Cross("2.10.6", "2.11.8", "2.12.4")
+            if !(platform == "native0.3" && scalaVersion == "2.10.6")
+          } yield new Module{
+            def suffix = Seq(scalaVersion, platform).filter(_.nonEmpty).map("_"+_).mkString
+          }
+      }
+
+      val Some((gen, innerMirror)) = Discovered[outer.type]
+        .mirror
+        .children
+        .head._2
+        .asInstanceOf[Mirror[outer.type, outer.crossed.type]]
+        .crossChildren
+
+      val keys = gen(outer.crossed)
+      val expectedKeys = List(
+        List("2.10.6", ""),
+        List("2.11.8", ""),
+        List("2.12.4", ""),
+        List("2.10.6", "sjs0.6"),
+        List("2.11.8", "sjs0.6"),
+        List("2.12.4", "sjs0.6"),
+        List("2.11.8", "native0.3"),
+        List("2.12.4", "native0.3"),
+      )
+
+      assert(keys == expectedKeys)
+      for(k <- keys){
+        val suffix = outer.crossed(k).suffix
+        val expected = k.map(_.toString).filter(_.nonEmpty).map("_"+_).mkString
+        assert(suffix == expected)
+      }
+    }
+    'crossCommands - {
+      object outer {
+        val cross = for (c <- mill.define.Cross("a", "b", "c")) yield new mill.Module {
+          def printIt() = T.command {
+            println("PRINTING IT: " + c)
+          }
+        }
+      }
+    }
+  }
+}
+
diff --git a/core/src/test/scala/mill/discover/DiscoveredTests.scala b/core/src/test/scala/mill/discover/DiscoveredTests.scala
index e9170967..b09ff2de 100644
--- a/core/src/test/scala/mill/discover/DiscoveredTests.scala
+++ b/core/src/test/scala/mill/discover/DiscoveredTests.scala
@@ -33,7 +33,7 @@ object DiscoveredTests extends TestSuite{
 
 
       def flatten(h: Mirror[outer.type, _]): Seq[Any] = {
-        h.node(outer) :: h.children.flatMap{case (label, c) => flatten(c)}
+        h.node(outer, Nil) :: h.children.flatMap{case (label, c) => flatten(c)}
       }
       val flattenedHierarchy = flatten(discovered.mirror)
 
@@ -44,7 +44,7 @@ object DiscoveredTests extends TestSuite{
       )
       assert(flattenedHierarchy == expectedHierarchy)
 
-      val mapped = discovered.targets(outer).map(x => x.segments -> x.target)
+      val mapped = discovered.targets(outer, Nil).map(x => x.segments -> x.target)
 
       val expected = Seq(
         (List("classInstance", "single"), outer.classInstance.single),