Avoid in ConstantTypes

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

@@ -5736,6 +5736,12 @@ object Types {
         case tp @ SuperType(thistp, supertp) =>
           derivedSuperType(tp, this(thistp), this(supertp))
 
+        case tp @ ConstantType(const @ Constant(_: Type)) =>
+          val classType = const.tpe
+          val classType1 = this(classType)
+          if classType eq classType1 then tp
+          else classType1
+
         case tp: LazyRef =>
           LazyRef { refCtx =>
             given Context = refCtx

compiler/src/dotty/tools/dotc/printing/Formatting.scala

@@ -71,6 +71,16 @@ object Formatting {
       given Show[TypeComparer.ApproxState] with
         def show(x: TypeComparer.ApproxState) = TypeComparer.ApproxState.Repr.show(x)
 
+      given Show[ast.TreeInfo.PurityLevel] with
+        def show(x: ast.TreeInfo.PurityLevel) = x match
+          case ast.TreeInfo.Path           => "PurityLevel.Path"
+          case ast.TreeInfo.Pure           => "PurityLevel.Pure"
+          case ast.TreeInfo.Idempotent     => "PurityLevel.Idempotent"
+          case ast.TreeInfo.Impure         => "PurityLevel.Impure"
+          case ast.TreeInfo.PurePath       => "PurityLevel.PurePath"
+          case ast.TreeInfo.IdempotentPath => "PurityLevel.IdempotentPath"
+          case _                           => s"PurityLevel(${x.x})"
+
       given Show[Showable]                            = ShowAny
       given Show[Shown]                               = ShowAny
       given Show[Int]                                 = ShowAny

tests/pos/i16954.scala

@@ -0,0 +1,18 @@
+class Test:
+  def test =
+    classOf[Test]
+
+  def blck =
+    class Blck
+    val cls = classOf[Blck]
+    cls
+
+  def expr =
+    class Expr
+    classOf[Expr] // was: "assertion failed: leak: Expr in { [..] }" crash
+
+object Test extends Test:
+  def main(args: Array[String]): Unit =
+    assert(test.getName == "Test",        test.getName)
+    assert(blck.getName == "Test$Blck$1", blck.getName)
+    assert(expr.getName == "Test$Expr$1", expr.getName)