First pass at using a compiler plugin to remove the need for the `override` keyword when overriding a field within a `mill.Module`

This only applies to `mill.Module`s, not overrides elsewhere which still require the keyword. `mill.Module`s tend to have lots and lots of overriding, so the keyword is basically noise.

Also includes the necessary build changes to enable the locally-built Scalac plugin when compiling the test suite. Note that no changes are necessary for the executable assembly, because the `scalac-plugin.xml` will be included in the assembly and get picked up by the Ammonite scalac plugin classloader automatically

3 files changed, 18 insertions, 38 deletions

diff --git a/core/src/main/scala/mill/define/Cacher.scala b/core/src/main/scala/mill/define/Cacher.scala
deleted file mode 100644
index 09200203..00000000
--- a/core/src/main/scala/mill/define/Cacher.scala
+++ /dev/null
@@ -1,33 +0,0 @@
-package mill.define
-
-import scala.collection.mutable
-import scala.reflect.macros.blackbox.Context
-
-
-trait Cacher[C[_]]{
-  private[this] val cacherLazyMap = mutable.Map.empty[sourcecode.Enclosing, C[_]]
-  def wrapCached[T](in: C[T], enclosing: String): C[T]
-  protected[this] def cachedTarget[T](t: => C[T])
-                                     (implicit c: sourcecode.Enclosing): C[T] = synchronized{
-    cacherLazyMap.getOrElseUpdate(c, wrapCached(t, c.value)).asInstanceOf[C[T]]
-  }
-}
-object Cacher{
-  def impl0[M[_], T: c.WeakTypeTag](c: Context)(t: c.Expr[M[T]]): c.Expr[M[T]] = {
-    c.Expr[M[T]](wrapCached(c)(t.tree))
-  }
-  def wrapCached(c: Context)(t: c.Tree) = {
-
-    import c.universe._
-    val owner = c.internal.enclosingOwner
-    val ownerIsCacherClass =
-      owner.owner.isClass &&
-      owner.owner.asClass.baseClasses.exists(_.fullName == "mill.define.Cacher")
-
-    if (ownerIsCacherClass && owner.isMethod) q"this.cachedTarget($t)"
-    else c.abort(
-      c.enclosingPosition,
-      "T{} members must be defs defined in a Cacher class/trait/object body"
-    )
-  }
-}
\ 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 e88ad8c6..8393acfb 100644
--- a/core/src/main/scala/mill/define/Task.scala
+++ b/core/src/main/scala/mill/define/Task.scala
@@ -58,7 +58,7 @@ object Target extends Applicative.Applyer[Task, Task, Result, Ctx]{
     import c.universe._
 
     c.Expr[Persistent[T]](
-      mill.define.Cacher.wrapCached(c)(
+      mill.plugin.Cacher.wrapCached(c)(
         q"new ${weakTypeOf[Persistent[T]]}(${Applicative.impl[Task, T, Ctx](c)(t).tree})"
       )
     )
@@ -74,7 +74,7 @@ object Target extends Applicative.Applyer[Task, Task, Result, Ctx]{
   def targetTaskImpl[T: c.WeakTypeTag](c: Context)(t: c.Expr[Task[T]]): c.Expr[Target[T]] = {
     import c.universe._
     c.Expr[Target[T]](
-      mill.define.Cacher.wrapCached(c)(
+      mill.plugin.Cacher.wrapCached(c)(
         q"new ${weakTypeOf[TargetImpl[T]]}($t, _root_.sourcecode.Enclosing())"
       )
     )
@@ -82,7 +82,7 @@ object Target extends Applicative.Applyer[Task, Task, Result, Ctx]{
   def targetImpl[T: c.WeakTypeTag](c: Context)(t: c.Expr[T]): c.Expr[Target[T]] = {
     import c.universe._
     c.Expr[Target[T]](
-      mill.define.Cacher.wrapCached(c)(
+      mill.plugin.Cacher.wrapCached(c)(
         q"new ${weakTypeOf[TargetImpl[T]]}(${Applicative.impl0[Task, T, Ctx](c)(q"mill.eval.Result.Success($t)").tree}, _root_.sourcecode.Enclosing())"
       )
     )
@@ -159,7 +159,7 @@ object Task {
   trait TaskModule extends Module {
     def defaultCommandName(): String
   }
-  trait Module extends mill.define.Cacher[Target]{
+  trait Module extends mill.plugin.Cacher[Target]{
     def wrapCached[T](t: Target[T], enclosing: String): Target[T] = t
   }
 
diff --git a/core/src/test/scala/mill/define/CacherTests.scala b/core/src/test/scala/mill/define/CacherTests.scala
index bacfa598..4b8e31ab 100644
--- a/core/src/test/scala/mill/define/CacherTests.scala
+++ b/core/src/test/scala/mill/define/CacherTests.scala
@@ -14,7 +14,7 @@ object CacherTests extends TestSuite{
   }
   object Middle extends Middle
   trait Middle extends Base{
-    override def value = T{ super.value() + 2}
+    def value = T{ super.value() + 2}
     def overriden = T{ super.value()}
   }
   object Terminal extends Terminal
@@ -49,6 +49,19 @@ object CacherTests extends TestSuite{
       eval(Terminal, Terminal.value) == 7,
       eval(Terminal, Terminal.overriden) == 1
     )
+    //    Doesn't fail, presumably compileError doesn't go far enough in the
+    //    compilation pipeline to hit the override checks
+    //
+    //    'overrideOutsideModuleFails - {
+    //      compileError("""
+    //        trait Foo{
+    //          def x = 1
+    //        }
+    //        object Bar extends Foo{
+    //          def x = 2
+    //        }
+    //      """)
+    //    }
   }
 }