Address review comments

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

@@ -108,7 +108,5 @@ object CaptureRoot:
   end isEnclosingRoot
 end CaptureRoot
 
-//class LevelError(val rvar: RootVar, val newBound: Symbol, val isUpper: Boolean) extends Exception
-
 
 

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

@@ -242,14 +242,15 @@ extends tpd.TreeTraverser:
           mapOverFollowingAliases(t)
 
   private def transformExplicitType(tp: Type, boxed: Boolean, mapRoots: Boolean)(using Context): Type =
-    val tp1 = expandAliases(if boxed then box(tp) else tp)
+    val tp1 = expandAliases(tp)
     val tp2 =
       if mapRoots
       then cc.mapRoots(defn.captureRoot.termRef, ctx.owner.localRoot.termRef)(tp1)
             .showing(i"map roots $tp1, ${tp1.getClass} == $result", capt)
       else tp1
-    if tp2 ne tp then capt.println(i"expanded: $tp --> $tp2")
-    tp2
+    val tp3 = if boxed then box(tp2) else tp2
+    if tp3 ne tp then capt.println(i"expanded: $tp --> $tp3")
+    tp3
 
   /** Transform type of type tree, and remember the transformed type as the type the tree */
   private def transformTT(tree: TypeTree, boxed: Boolean, exact: Boolean, mapRoots: Boolean)(using Context): Unit =
@@ -463,8 +464,8 @@ extends tpd.TreeTraverser:
               newInfo
             else new LazyType:
               def complete(denot: SymDenotation)(using Context) =
-                // infos other methods are determined from their definitions which
-                // are checked on depand
+                // infos of other methods are determined from their definitions which
+                // are checked on demand
                 denot.info = newInfo
                 recheckDef(tree, sym))
         else updateOwner(sym)

compiler/src/dotty/tools/dotc/util/SimpleIdentitySet.scala

@@ -142,8 +142,10 @@ object SimpleIdentitySet {
       val y0 = f(x0.asInstanceOf[Elem])
       val y1 = f(x1.asInstanceOf[Elem])
       val y2 = f(x2.asInstanceOf[Elem])
-      if (y0 ne y1) && (y0 ne y2) && (y1 ne y2) then Set3(y0, y1, y2)
-      else super.map(f)
+      if y1 eq y0 then
+        if y2 eq y0 then Set1(y0) else Set2(y0, y2)
+      else if (y2 eq y0) || (y2 eq y1) then Set2(y0, y1)
+      else Set3(y0, y1, y2)
     def /: [A, E >: Elem <: AnyRef](z: A)(f: (A, E) => A): A =
       f(f(f(z, x0.asInstanceOf[E]), x1.asInstanceOf[E]), x2.asInstanceOf[E])
     def toList = x0.asInstanceOf[Elem] :: x1.asInstanceOf[Elem] :: x2.asInstanceOf[Elem] :: Nil

tests/neg-custom-args/captures/box-unsoundness.scala

@@ -0,0 +1,6 @@
+@annotation.capability class CanIO { def use(): Unit = () }
+def use[X](x: X): (op: X -> Unit) -> Unit = op => op(x)
+def test(io: CanIO): Unit =
+  val f = use[CanIO](io)
+  val g: () -> Unit = () => f(x => x.use())  // error
+  // was UNSOUND: g uses the capability io but has an empty capture set