Box arguments of type applications

This required a change in `lists.scala`, where capture sets buried to the right had
to be repeated on the whole type. I believe there is no desugaring yet that would do
these things automatically.

Author: odersky

compiler/src/dotty/tools/dotc/cc/Setup.scala

@@ -333,7 +333,7 @@ extends tpd.TreeTraverser:
         mapOver(t)
   end SubstParams
 
-  private def transformTT(tree: TypeTree, boxed: Boolean)(using Context) =
+  private def transformTT(tree: TypeTree, boxed: Boolean)(using Context): Unit =
     tree.rememberType(
       if tree.isInstanceOf[InferredTypeTree]
       then transformInferredType(tree.tpe, boxed)
@@ -349,6 +349,10 @@ extends tpd.TreeTraverser:
       case tree @ ValDef(_, tpt: TypeTree, _) if tree.symbol.is(Mutable) =>
         transformTT(tpt, boxed = true)
         traverse(tree.rhs)
+      case tree @ TypeApply(fn, args) =>
+        traverse(fn)
+        for case arg: TypeTree <- args do
+          transformTT(arg, boxed = true)
       case _ =>
         traverseChildren(tree)
     tree match

tests/pos-custom-args/captures/lists.scala

@@ -50,7 +50,7 @@ def test(c: Cap, d: Cap, e: Cap) =
   val eff2 = [A] => (x: A) => if x == e then x else x
 
   val a0 = identity[{d, y} Cap -> Unit]
-  val a0c: ({d, y} Cap -> Unit) -> {d, y} Cap -> Unit = a0
+  val a0c: {d, y} ({d, y} Cap -> Unit) -> {d, y} Cap -> Unit = a0
   val a1 = zs.map[{d, y} Cap -> Unit](a0)
   val a1c: LIST[{d, y} Cap -> Unit] = a1
   val a2 = zs.map[{d, y} Cap -> Unit](identity[{d, y} Cap -> Unit])
@@ -65,7 +65,7 @@ def test(c: Cap, d: Cap, e: Cap) =
   val a6c: LIST[{d, c} Cap -> Unit] = a6
 
   val b0 = eff[{d, y} Cap -> Unit]
-  val b0c: {e} ({d, y} Cap -> Unit) -> {d, y} Cap -> Unit = b0
+  val b0c: {e, d, y} ({d, y} Cap -> Unit) -> {d, y} Cap -> Unit = b0
   val b1 = zs.map[{d, y} Cap -> Unit](a0)
   val b1c: {e} LIST[{d, y} Cap -> Unit] = b1
   val b2 = zs.map[{d, y} Cap -> Unit](eff[{d, y} Cap -> Unit])
@@ -80,7 +80,7 @@ def test(c: Cap, d: Cap, e: Cap) =
   val b6c: {e} LIST[{d, c} Cap -> Unit] = b6
 
   val c0 = eff2[{d, y} Cap -> Unit]
-  val c0c: {e} ({d, y} Cap -> Unit) -> {d, y} Cap -> Unit = c0
+  val c0c: {e, d, y} ({d, y} Cap -> Unit) -> {d, y} Cap -> Unit = c0
   val c1 = zs.map[{d, y} Cap -> Unit](a0)
   val c1c: {e} LIST[{d, y} Cap -> Unit] = c1
   val c2 = zs.map[{d, y} Cap -> Unit](eff2[{d, y} Cap -> Unit])