1 files changed, 81 insertions, 0 deletions
diff --git a/core/src/mill/main/Resolve.scala b/core/src/mill/main/Resolve.scala
new file mode 100644
index 00000000..ed4c4f80
--- /dev/null
+++ b/core/src/mill/main/Resolve.scala
@@ -0,0 +1,81 @@
+package mill.main
+
+import mill.define._
+import mill.define.TaskModule
+import ammonite.main.Router
+import ammonite.main.Router.EntryPoint
+
+object Resolve {
+  def resolve[T, V](remainingSelector: List[Segment],
+                    obj: mill.Module,
+                    discover: Discover,
+                    rest: Seq[String],
+                    remainingCrossSelectors: List[List[String]],
+                    revSelectorsSoFar: List[Segment]): Either[String, Task[Any]] = {
+
+    remainingSelector match{
+      case Segment.Cross(_) :: Nil => Left("Selector cannot start with a [cross] segment")
+      case Segment.Label(last) :: Nil =>
+        val target =
+          obj
+            .millInternal
+            .reflect[Target[_]]
+            .find(_.label == last)
+            .map(Right(_))
+
+        def invokeCommand[V](target: mill.Module, name: String) = {
+          for(cmd <- discover.value.get(target.getClass).toSeq.flatten.find(_.name == name))
+          yield cmd.asInstanceOf[EntryPoint[mill.Module]].invoke(target, ammonite.main.Scripts.groupArgs(rest.toList)) match {
+            case Router.Result.Success(v) => Right(v)
+            case _ => Left(s"Command failed $last")
+          }
+        }
+
+        val runDefault = for{
+          child <- obj.millInternal.reflectNestedObjects[mill.Module]
+          if child.millOuterCtx.segment == Segment.Label(last)
+          res <- child match{
+            case taskMod: TaskModule => Some(invokeCommand(child, taskMod.defaultCommandName()))
+            case _ => None
+          }
+        } yield res
+
+        val command = invokeCommand(obj, last)
+
+        command orElse target orElse runDefault.headOption.flatten match{
+          case None =>  Left("Cannot resolve task " +
+            Segments((Segment.Label(last) :: revSelectorsSoFar).reverse:_*).render
+          )
+          // Contents of `either` *must* be a `Task`, because we only select
+          // methods returning `Task` in the discovery process
+          case Some(either) => either.right.map{ case x: Task[Any] => x }
+        }
+
+
+      case head :: tail =>
+        val newRevSelectorsSoFar = head :: revSelectorsSoFar
+        head match{
+          case Segment.Label(singleLabel) =>
+            obj.millInternal.reflectNestedObjects[mill.Module].find{
+              _.millOuterCtx.segment == Segment.Label(singleLabel)
+            } match{
+              case Some(child: mill.Module) => resolve(tail, child, discover, rest, remainingCrossSelectors, newRevSelectorsSoFar)
+              case None => Left("Cannot resolve module " + Segments(newRevSelectorsSoFar.reverse:_*).render)
+            }
+
+          case Segment.Cross(cross) =>
+            obj match{
+              case c: Cross[_] =>
+                c.itemMap.get(cross.toList) match{
+                  case Some(m: mill.Module) => resolve(tail, m, discover, rest, remainingCrossSelectors, newRevSelectorsSoFar)
+                  case None => Left("Cannot resolve cross " + Segments(newRevSelectorsSoFar.reverse:_*).render)
+
+                }
+              case _ => Left("Cannot resolve cross " + Segments(newRevSelectorsSoFar.reverse:_*).render)
+            }
+        }
+
+      case Nil => Left("Selector cannot be empty")
+    }
+  }
+}