First pass at implicitly propagating a `def basePath: Path` up the `Module` hierarchy, which each module receives and extends.

One constraint is that now must define your abstract modules as `trait`s rather than `class`es, or otherwise add an implicit `ctx: ModuleCtx` parameter to your class definition.

 So far this lets us remove some explicit `basePath` definitions in `build.sc`. Proper handling of `basePath` in `CrossModule`s is future work

4 files changed, 48 insertions, 14 deletions

diff --git a/core/src/main/scala/mill/define/Cross.scala b/core/src/main/scala/mill/define/Cross.scala
index 90a383a6..26eef933 100644
--- a/core/src/main/scala/mill/define/Cross.scala
+++ b/core/src/main/scala/mill/define/Cross.scala
@@ -28,4 +28,12 @@ object Cross{
 
 class CrossModule[T, V](constructor: T => V, cases: T*)
                        (implicit e: sourcecode.Enclosing, l: sourcecode.Line)
-extends Cross[V](cases.toList.map(x => (List(x), constructor(x))))
\ No newline at end of file
+extends Cross[V](cases.toList.map(x => (List(x), constructor(x))))
+
+class CrossModule2[T1, T2, V](constructor: (T1, T2) => V, cases: (T1, T2)*)
+                       (implicit e: sourcecode.Enclosing, l: sourcecode.Line)
+extends Cross[V](cases.toList.map(x => (List(x._2, x._1), constructor(x._1, x._2))))
+
+class CrossModule3[T1, T2, T3, V](constructor: (T1, T2, T3) => V, cases: (T1, T2, T3)*)
+                       (implicit e: sourcecode.Enclosing, l: sourcecode.Line)
+extends Cross[V](cases.toList.map(x => (List(x._3, x._2, x._1), constructor(x._1, x._2, x._3))))
\ No newline at end of file
diff --git a/core/src/main/scala/mill/define/Task.scala b/core/src/main/scala/mill/define/Task.scala
index 6ee9c606..0704c7c8 100644
--- a/core/src/main/scala/mill/define/Task.scala
+++ b/core/src/main/scala/mill/define/Task.scala
@@ -1,6 +1,7 @@
 package mill.define
 
 import ammonite.main.Router.Overrides
+import ammonite.ops.Path
 import mill.define.Applicative.Applyable
 import mill.eval.{PathRef, Result}
 import mill.util.Ctx
@@ -361,10 +362,9 @@ class Input[T](t: Task[T],
   def evaluate(args: Ctx) = args[T](0)
   override def sideHash = util.Random.nextInt()
 }
-
+case class BasePath(value: Path)
 object Task {
 
-
   trait TaskModule extends Module {
     def defaultCommandName(): String
   }
@@ -375,14 +375,37 @@ object Task {
     * instantiation site so they can capture the enclosing/line information of
     * the concrete instance.
     */
-  class Module(implicit millModuleEnclosing0: sourcecode.Enclosing,
-               millModuleLine0: sourcecode.Line) extends mill.moduledefs.Cacher{
+  class Module(implicit ctx: Module.Ctx) extends mill.moduledefs.Cacher{
     // Ensure we do not propagate the implicit parameters as implicits within
     // the body of any inheriting class/trait/objects, as it would screw up any
     // one else trying to use sourcecode.{Enclosing,Line} to capture debug info
-    val millModuleEnclosing = millModuleEnclosing0
-    val millModuleLine = millModuleLine0
+    val millModuleEnclosing = ctx.millModuleEnclosing0
+    val millModuleLine = ctx.millModuleLine0
+    def basePath: Path = ctx.millModuleBasePath0.value / ctx.millName0.value
+    implicit def millModuleBasePath: BasePath = BasePath(basePath)
+  }
+  object Module{
+    case class Ctx(millModuleEnclosing0: sourcecode.Enclosing,
+                   millModuleLine0: sourcecode.Line,
+                   millName0: sourcecode.Name,
+                   millModuleBasePath0: BasePath)
+    object Ctx{
+      implicit def make(implicit millModuleEnclosing0: sourcecode.Enclosing,
+                        millModuleLine0: sourcecode.Line,
+                        millName0: sourcecode.Name,
+                        millModuleBasePath0: BasePath): Ctx = Ctx(
+        millModuleEnclosing0,
+        millModuleLine0,
+        millName0,
+        millModuleBasePath0
+      )
+    }
   }
+  class BaseModule(basePath: Path)
+                  (implicit millModuleEnclosing0: sourcecode.Enclosing,
+                   millModuleLine0: sourcecode.Line,
+                   millName0: sourcecode.Name)
+    extends Module()(Module.Ctx.make(implicitly, implicitly, implicitly, BasePath(basePath)))
 
   class Task0[T](t: T) extends Task[T]{
     lazy val t0 = t
diff --git a/core/src/main/scala/mill/main/MainRunner.scala b/core/src/main/scala/mill/main/MainRunner.scala
index 76e2d069..322795ea 100644
--- a/core/src/main/scala/mill/main/MainRunner.scala
+++ b/core/src/main/scala/mill/main/MainRunner.scala
@@ -75,15 +75,12 @@ class MainRunner(config: ammonite.main.Cli.Config,
   }
   override def initMain(isRepl: Boolean) = {
     super.initMain(isRepl).copy(
-      scriptCodeWrapper = mill.main.MainRunner.CustomCodeWrapper,
+      scriptCodeWrapper = CustomCodeWrapper,
       // Ammonite does not properly forward the wd from CliConfig to Main, so
       // force forward it outselves
       wd = config.wd
     )
   }
-}
-
-object MainRunner{
   object CustomCodeWrapper extends Preprocessor.CodeWrapper {
     def top(pkgName: Seq[Name], imports: Imports, indexedWrapperName: Name) = {
       val wrapName = indexedWrapperName.backticked
@@ -93,14 +90,17 @@ object MainRunner{
          |$imports
          |import mill._
          |
-         |object $wrapName extends $wrapName{
+         |object $wrapName extends mill.define.Task.BaseModule(ammonite.ops.Path(${pprint.Util.literalize(config.wd.toString)})) with $wrapName{
+         |  // Make sure we don't include the `build` wrapper-object's name in
+         |  // the `basePath`s of our build
+         |  override def basePath = super.basePath / ammonite.ops.up
          |  // Stub to make sure Ammonite has something to call after it evaluates a script,
          |  // even if it does nothing...
          |  def $$main() = Iterator[String]()
          |  lazy val mapping = mill.discover.Discovered.make[$wrapName].mapping(this)
          |}
          |
-         |sealed abstract class $wrapName extends mill.Module{
+         |sealed trait $wrapName extends mill.Module{
          |""".stripMargin
     }
 
@@ -112,4 +112,4 @@ object MainRunner{
       "\n}"
     }
   }
-}
\ No newline at end of file
+}
diff --git a/core/src/main/scala/mill/package.scala b/core/src/main/scala/mill/package.scala
index b7332f9e..f833b82c 100644
--- a/core/src/main/scala/mill/package.scala
+++ b/core/src/main/scala/mill/package.scala
@@ -6,5 +6,8 @@ package object mill extends JsonFormatters{
   val PathRef = mill.eval.PathRef
   type PathRef = mill.eval.PathRef
   type Module = define.Task.Module
+  val Module = define.Task.Module
   type CrossModule[T, V] = define.CrossModule[T, V]
+  type CrossModule2[T1, T2, V] = define.CrossModule2[T1, T2, V]
+  type CrossModule3[T1, T2, T3, V] = define.CrossModule3[T1, T2, T3, V]
 }