Add stub mill.define.Ctx to trick IntelliJ into not erroring

main/define/src/mill/define/Cacher.scala

@@ -0,0 +1,33 @@
+package mill.define
+
+import scala.collection.mutable
+import scala.reflect.macros.blackbox.Context
+
+private[mill] trait Cacher extends mill.moduledefs.Cacher {
+  private[this] lazy val cacherLazyMap = mutable.Map.empty[sourcecode.Enclosing, Any]
+
+  override protected[this] def cachedTarget[T](t: => T)(implicit c: sourcecode.Enclosing): T =
+    synchronized {
+      cacherLazyMap.getOrElseUpdate(c, t).asInstanceOf[T]
+    }
+}
+
+private[mill] object Cacher {
+  def impl0[T: c.WeakTypeTag](c: Context)(t: c.Expr[T]): c.Expr[T] = {
+    c.Expr[T](wrapCached[T](c)(t.tree))
+  }
+  def wrapCached[R: c.WeakTypeTag](c: Context)(t: c.Tree): c.universe.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[${weakTypeTag[R]}]($t)"
+    else c.abort(
+      c.enclosingPosition,
+      "Task{} members must be defs defined in a Module class/trait/object body"
+    )
+  }
+}

main/define/src/mill/define/Ctx.scala

@@ -1,6 +1,6 @@
 package mill.define
 
-import scala.annotation.implicitNotFound
+import scala.annotation.{compileTimeOnly, implicitNotFound}
 
 /**
  * The contextual information provided by a [[mill.define.Module]].
@@ -39,7 +39,7 @@ trait Ctx {
   private[mill] def withEnclosingModule(enclosingModule: Any): Ctx = this
 }
 
-object Ctx {
+object Ctx extends LowPriCtx {
   private case class Impl(
       enclosing: String,
       lineNum: Int,
@@ -106,3 +106,13 @@ object Ctx {
     )
   }
 }
+
+trait LowPriCtx {
+  // Dummy `Ctx` available in implicit scope but never actually used.
+  // as it is provided by the codegen. Defined for IDEs to think that one is available
+  // and not show errors in build.mill/package.mill even though they can't see the codegen
+  @compileTimeOnly(
+    "Modules and Tasks can only be defined within a mill Module"
+  )
+  implicit def dummyInfo: Ctx = sys.error("implicit Ctx must be provided")
+}

main/define/src/mill/define/Module.scala

@@ -55,7 +55,7 @@ object Module {
    * messes up the module discovery process
    */
   @internal
-  class BaseClass(implicit outerCtx0: mill.define.Ctx) extends mill.moduledefs.Cacher {
+  class BaseClass(implicit outerCtx0: mill.define.Ctx) extends mill.define.Cacher {
     def millOuterCtx = outerCtx0
   }
 

main/define/src/mill/define/Task.scala

@@ -359,7 +359,7 @@ object Target extends TaskBase {
 
       val lhs = Applicative.impl0[Task, T, mill.api.Ctx](c)(reify(Result.create(t.splice)).tree)
 
-      mill.moduledefs.Cacher.impl0[Target[T]](c)(
+      mill.define.Cacher.impl0[Target[T]](c)(
         reify(
           new TargetImpl[T](
             lhs.splice,
@@ -379,7 +379,7 @@ object Target extends TaskBase {
 
       val taskIsPrivate = isPrivateTargetOption(c)
 
-      mill.moduledefs.Cacher.impl0[Target[T]](c)(
+      mill.define.Cacher.impl0[Target[T]](c)(
         reify(
           new TargetImpl[T](
             Applicative.impl0[Task, T, mill.api.Ctx](c)(t.tree).splice,
@@ -398,7 +398,7 @@ object Target extends TaskBase {
 
       val taskIsPrivate = isPrivateTargetOption(c)
 
-      mill.moduledefs.Cacher.impl0[Target[T]](c)(
+      mill.define.Cacher.impl0[Target[T]](c)(
         reify {
           val s1 = Applicative.impl0[Task, T, mill.api.Ctx](c)(t.tree).splice
           val c1 = ctx.splice
@@ -421,7 +421,7 @@ object Target extends TaskBase {
 
       val taskIsPrivate = isPrivateTargetOption(c)
 
-      mill.moduledefs.Cacher.impl0[Target[T]](c)(
+      mill.define.Cacher.impl0[Target[T]](c)(
         reify(
           new TargetImpl[T](
             t.splice,
@@ -444,7 +444,7 @@ object Target extends TaskBase {
 
       val taskIsPrivate = isPrivateTargetOption(c)
 
-      mill.moduledefs.Cacher.impl0[SourcesImpl](c)(
+      mill.define.Cacher.impl0[SourcesImpl](c)(
         reify(
           new SourcesImpl(
             Target.sequence(c.Expr[List[Task[PathRef]]](q"_root_.scala.List(..$wrapped)").splice),
@@ -461,7 +461,7 @@ object Target extends TaskBase {
 
       val taskIsPrivate = isPrivateTargetOption(c)
 
-      mill.moduledefs.Cacher.impl0[SourcesImpl](c)(
+      mill.define.Cacher.impl0[SourcesImpl](c)(
         reify(
           new SourcesImpl(
             Applicative.impl0[Task, Seq[PathRef], mill.api.Ctx](c)(values.tree).splice,
@@ -483,7 +483,7 @@ object Target extends TaskBase {
 
       val taskIsPrivate = isPrivateTargetOption(c)
 
-      mill.moduledefs.Cacher.impl0[Target[PathRef]](c)(
+      mill.define.Cacher.impl0[Target[PathRef]](c)(
         reify(
           new SourceImpl(
             wrapped.splice,
@@ -500,7 +500,7 @@ object Target extends TaskBase {
 
       val taskIsPrivate = isPrivateTargetOption(c)
 
-      mill.moduledefs.Cacher.impl0[Target[PathRef]](c)(
+      mill.define.Cacher.impl0[Target[PathRef]](c)(
         reify(
           new SourceImpl(
             Applicative.impl0[Task, PathRef, mill.api.Ctx](c)(value.tree).splice,
@@ -519,7 +519,7 @@ object Target extends TaskBase {
 
       val taskIsPrivate = isPrivateTargetOption(c)
 
-      mill.moduledefs.Cacher.impl0[InputImpl[T]](c)(
+      mill.define.Cacher.impl0[InputImpl[T]](c)(
         reify(
           new InputImpl[T](
             Applicative.impl[Task, T, mill.api.Ctx](c)(value).splice,
@@ -598,7 +598,7 @@ object Target extends TaskBase {
 
       val taskIsPrivate = isPrivateTargetOption(c)
 
-      mill.moduledefs.Cacher.impl0[Worker[T]](c)(
+      mill.define.Cacher.impl0[Worker[T]](c)(
         reify(
           new Worker[T](t.splice, ctx.splice, taskIsPrivate.splice)
         )
@@ -611,7 +611,7 @@ object Target extends TaskBase {
 
       val taskIsPrivate = isPrivateTargetOption(c)
 
-      mill.moduledefs.Cacher.impl0[Worker[T]](c)(
+      mill.define.Cacher.impl0[Worker[T]](c)(
         reify(
           new Worker[T](
             Applicative.impl[Task, T, mill.api.Ctx](c)(t).splice,
@@ -630,7 +630,7 @@ object Target extends TaskBase {
 
       val taskIsPrivate = isPrivateTargetOption(c)
 
-      mill.moduledefs.Cacher.impl0[PersistentImpl[T]](c)(
+      mill.define.Cacher.impl0[PersistentImpl[T]](c)(
         reify(
           new PersistentImpl[T](
             Applicative.impl[Task, T, mill.api.Ctx](c)(t).splice,

main/define/test/src/mill/define/MacroErrorTests.scala

@@ -10,7 +10,7 @@ object MacroErrorTests extends TestSuite {
 
     test("errors") {
       val expectedMsg =
-        "Task{} members must be defs defined in a Cacher class/trait/object body"
+        "Task{} members must be defs defined in a Module class/trait/object body"
 
       val err = compileError("object Foo extends TestBaseModule{ val x = Task {1} }")
       assert(err.msg == expectedMsg)
@@ -84,21 +84,32 @@ object MacroErrorTests extends TestSuite {
       // of our `Target#apply()` calls, but we cannot reference any values that
       // come from inside the Task{...} block
       test("pos") {
-        val e = compileError("""
-          val a = Task { 1 }
+        // This hsould compile
+        object foo extends TestBaseModule {
+          def a = Task { 1 }
           val arr = Array(a)
-          val b = {
+          def b = {
             val c = 0
-            Task{
+            Task {
               arr(c)()
             }
           }
-        """)
+        }
+      }
+      test("neg1") {
+        val e = compileError("""def a = Task { 1 }""")
         assert(e.msg.contains(
-          "Modules and Tasks can only be defined within a mill Module"
+          "Task{} members must be defs defined in a Module class/trait/object body"
         ))
       }
-      test("neg") {
+
+      test("neg2") {
+        val e = compileError("object foo extends TestBaseModule{ val a = Task { 1 } }")
+        assert(e.msg.contains(
+          "Task{} members must be defs defined in a Module class/trait/object body"
+        ))
+      }
+      test("neg3") {
 
         val expectedMsg =
           "Target#apply() call cannot use `value n` defined within the Task{...} block"
@@ -114,7 +125,7 @@ object MacroErrorTests extends TestSuite {
         }""")
         assert(err.msg == expectedMsg)
       }
-      test("neg2") {
+      test("neg4") {
 
         val expectedMsg =
           "Target#apply() call cannot use `value x` defined within the Task{...} block"
@@ -129,7 +140,7 @@ object MacroErrorTests extends TestSuite {
         }""")
         assert(err.msg == expectedMsg)
       }
-      test("neg3") {
+      test("neg5") {
         val borkedCachedDiamond1 = utest.compileError("""
           object borkedCachedDiamond1 {
             def up = Task { TestUtil.test() }
@@ -139,7 +150,7 @@ object MacroErrorTests extends TestSuite {
           }
         """)
         assert(borkedCachedDiamond1.msg.contains(
-          "Modules and Tasks can only be defined within a mill Module"
+          "Task{} members must be defs defined in a Module class/trait/object body"
         ))
       }
     }