Fix noCaptures condition

Author: odersky

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -1514,7 +1514,14 @@ object Types {
 
     def captureSet(using Context): CaptureSet = CaptureSet.ofType(this)
     def noCaptures(using Context): Boolean =
-      ctx.mode.is(Mode.RelaxedCapturing) || captureSet.isEmpty
+      ctx.mode.is(Mode.RelaxedCapturing) || allCaptures.isEmpty
+
+    def allCaptures(using Context): CaptureSet = this match // ^^^^ optimize, relate with boxedCaptures?
+      case tp: CapturingType => tp.refs
+      case tp: TypeProxy => tp.superType.allCaptures
+      case tp: AndType => tp.tp1.allCaptures ++ tp.tp2.allCaptures
+      case tp: OrType => tp.tp1.allCaptures ** tp.tp2.allCaptures
+      case _ => CaptureSet.empty
 
     // ----- Normalizing typerefs over refined types ----------------------------
 

tests/pos-custom-args/captures/boxmap-paper.scala

@@ -6,6 +6,8 @@ type Cell[+T <: Top] = [K] => (T ==> K) => K
 def cell[T <: Top](x: T): Cell[T] =
   [K] => (k: T ==> K) => k(x)
 
+def identity[T <: Top](x: T): T = x
+
 def get[T <: Top](c: Cell[T]): T = c[T](identity)
 
 def map[A <: Top, B <: Top](c: Cell[A])(f: A ==> B): Cell[B]

tests/pos-custom-args/captures/list-encoding.scala

@@ -19,6 +19,6 @@ def foo(c: {*} Cap) =
   def f(x: String retains c.type, y: String retains c.type) =
     cons(x, cons(y, nil))
   def g(x: String retains c.type, y: Any) =
-    cons(x, cons(y, nil))
+    cons[{c} Any](x, cons[Any](y, nil))  // TODO: drop type arguments
   def h(x: String, y: Any retains c.type) =
     cons(x, cons(y, nil))