Fix scala#11464: avoid expanding local paramRef in HKTypeLambda

Author: liufengyun

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

@@ -401,6 +401,7 @@ object TypeOps:
   def avoid(tp: Type, symsToAvoid: => List[Symbol])(using Context): Type = {
     val widenMap = new ApproximatingTypeMap {
       @threadUnsafe lazy val forbidden = symsToAvoid.toSet
+      val locals = util.HashSet[Type]()
       def toAvoid(sym: Symbol) = !sym.isStatic && forbidden.contains(sym)
       def partsToAvoid = new NamedPartsAccumulator(tp => toAvoid(tp.symbol))
 
@@ -429,17 +430,22 @@ object TypeOps:
             case _ =>
               emptyRange // should happen only in error cases
           }
-        case tp: ThisType if toAvoid(tp.cls) =>
-          range(defn.NothingType, apply(classBound(tp.cls.classInfo)))
+        case tp: ThisType =>
+          tp
         case tp: SkolemType if partsToAvoid(Nil, tp.info).nonEmpty =>
           range(defn.NothingType, apply(tp.info))
         case tp: TypeVar if mapCtx.typerState.constraint.contains(tp) =>
           val lo = TypeComparer.instanceType(
             tp.origin, fromBelow = variance > 0 || variance == 0 && tp.hasLowerBound)(using mapCtx)
           val lo1 = apply(lo)
           if (lo1 ne lo) lo1 else tp
-        case tp: LazyRef if isExpandingBounds =>
-          emptyRange
+        case tp: LazyRef =>
+          if locals.contains(tp.ref) then tp
+          else if isExpandingBounds then emptyRange
+          else mapOver(tp)
+        case tl: HKTypeLambda =>
+          locals ++= tl.paramRefs
+          mapOver(tl)
         case _ =>
           mapOver(tp)
       }

tests/pos/i11464.scala

@@ -0,0 +1,16 @@
+trait Txn[T <: Txn[T]]
+
+trait Adjunct
+
+trait Type0
+trait Type[A1, Repr[~ <: Txn[~]] <: Expr[~, A1]] extends Type0
+
+object Expr {
+  def test(peer: Type0): Adjunct = {
+    new AdjunctImpl(peer.asInstanceOf[Type[Any, ({ type R[~ <: Txn[~]] <: Expr[~, Any] }) # R]])
+  }
+}
+
+trait Expr[T <: Txn[T], +A]
+
+class AdjunctImpl[A, E[~ <: Txn[~]] <: Expr[~, A]](tpe: Type[A, E]) extends Adjunct