Undo AvoidMap changes + patch CaptureRef.subsumes

The underlying cause for the divergence in
cc-poly-varargs is that we could not conclude
that the capture variable `Cap^` subsumes `left`
through `src1`, i.e., `left` reaches `Cap^`.
That caused `left` to appear circularly in its
own capture set and subsequently avoidance to loop
forever.

Author: bracevac

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

@@ -108,7 +108,6 @@ trait CaptureRef extends TypeProxy, ValueType:
    *   TODO: Document cases with more comments.
    */
   final def subsumes(y: CaptureRef)(using Context): Boolean =
-
     def subsumingRefs(x: Type, y: Type): Boolean = x match
       case x: CaptureRef => y match
         case y: CaptureRef => x.subsumes(y)
@@ -119,6 +118,7 @@ trait CaptureRef extends TypeProxy, ValueType:
       case info: SingletonCaptureRef => test(info)
       case info: AndType => viaInfo(info.tp1)(test) || viaInfo(info.tp2)(test)
       case info: OrType => viaInfo(info.tp1)(test) && viaInfo(info.tp2)(test)
+      case info @ CapturingType(_,_) if this.derivesFrom(defn.Caps_CapSet) => test(info)
       case _ => false
 
     (this eq y)
@@ -149,7 +149,7 @@ trait CaptureRef extends TypeProxy, ValueType:
           y.info match
             case TypeBounds(_, hi: CaptureRef) => this.subsumes(hi)
             case _ => y.captureSetOfInfo.elems.forall(this.subsumes)
-        case CapturingType(parent, refs) if parent.derivesFrom(defn.Caps_CapSet) =>
+        case CapturingType(parent, refs) if parent.derivesFrom(defn.Caps_CapSet) || this.derivesFrom(defn.Caps_CapSet) =>
           refs.elems.forall(this.subsumes)
         case _ => false
     || this.match

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

@@ -298,15 +298,6 @@ sealed abstract class CaptureSet extends Showable:
       else BiMapped(asVar, tm, mappedElems)
     case tm: IdentityCaptRefMap =>
       this
-    case av: AvoidMap =>
-      val mapped = mapRefs(elems, ref => ref match
-        case n: NamedType if av.toAvoid(n) => empty //TODO what about variance?
-        case r => extrapolateCaptureRef(r, av, av.variance)
-      )
-      if isConst then
-        if mapped.isConst && mapped.elems == elems && !mapped.keepAlways then this
-        else mapped
-      else Mapped(asVar, av, av.variance, mapped)
     case _ =>
       val mapped = mapRefs(elems, tm, tm.variance)
       if isConst then