Fix #11464: avoid expanding local paramRef in HKTypeLambda

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
+      @threadUnsafe lazy val localParamRefs = util.HashSet[Type]()
       def toAvoid(sym: Symbol) = !sym.isStatic && forbidden.contains(sym)
       def partsToAvoid = new NamedPartsAccumulator(tp => toAvoid(tp.symbol))
 
@@ -429,17 +430,25 @@ 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 =>
+          // ThisType is only used inside a class.
+          // Therefore, either they don't appear in the type to be avoided, or
+          // it must be a class that encloses the block whose type is to be avoided.
+          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 localParamRefs.contains(tp.ref) then tp
+          else if isExpandingBounds then emptyRange
+          else mapOver(tp)
+        case tl: HKTypeLambda =>
+          localParamRefs ++= tl.paramRefs
+          mapOver(tl)
         case _ =>
           mapOver(tp)
       }

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

@@ -2924,7 +2924,7 @@ object Types {
           tp match {
             case tp: TypeRef => apply(x, tp.prefix)
             case tp: RecThis => RecType.this eq tp.binder
-            case tp: LazyRef => true // To be safe, assume a reference exists
+            case tp: LazyRef => this(x, tp.ref)
             case _ => foldOver(x, tp)
           }
         }

compiler/test/dotc/pos-test-pickling.blacklist

@@ -60,4 +60,3 @@ i9793.scala
 
 # lazy_implicit symbol has different position after pickling
 i8182.scala
-

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