Fixed bug where top-level classes are not allowed to have the @TargetNAME annotation, as of Scala 3.2

Author: Dean Wampler

src/main/scala/progscala3/typesystem/bounds/list/AbbrevList.scala

@@ -4,38 +4,48 @@ package progscala3.typesystem.bounds.list
 import scala.annotation.targetName
 import java.util.NoSuchElementException
 
-sealed abstract class AbbrevList[+A]:
-
-  def isEmpty: Boolean
-  def head: A
-  def tail: AbbrevList[A]
-
-  @targetName("prepend")
-  def ::[B >: A] (x: B): AbbrevList[B] = new ::(x, this)
-
-  final def foreach(f: A => Unit) =
-    var these = this
-    while !these.isEmpty do
-      f(these.head)
-      these = these.tail
-
-// The empty AbbrevList.
-
-case object AbbrevNil extends AbbrevList[Nothing]:
-  override def isEmpty = true
-
-  def head: Nothing =
-    throw NoSuchElementException("head of empty AbbrevList")
-
-  def tail: AbbrevList[Nothing] =
-    throw NoSuchElementException("tail of empty AbbrevList")
-
-// A non-empty AbbrevList characterized by a head and a tail.
-
-@targetName("AbbrevListCons")
-final case class ::[B](private var hd: B,
-    private[list] var tl: AbbrevList[B]) extends AbbrevList[B]:
-
-  override def isEmpty: Boolean = false
-  def head : B = hd
-  def tail : AbbrevList[B] = tl
+/**
+ * Scala 3.2 no longer allows top-level classes to have @targetName annotations.
+ * From the error message printed by the compiler:
+ *   This restriction is due to the naming convention of Java classfiles, whose filenames
+ *   are based on the name of the class defined within. If @targetName were permitted
+ *   here, the name of the classfile would be based on the target name, and the compiler
+ *   could not associate that classfile with the Scala-visible defined name of the class.
+ * One solution is to wrap the types in an object, as done here, which is not shown in the book.
+ */  
+object AbbrevListModule:
+  sealed abstract class AbbrevList[+A]:
+
+    def isEmpty: Boolean
+    def head: A
+    def tail: AbbrevList[A]
+
+    @targetName("prepend")
+    def ::[B >: A] (x: B): AbbrevList[B] = new ::(x, this)
+
+    final def foreach(f: A => Unit) =
+      var these = this
+      while !these.isEmpty do
+        f(these.head)
+        these = these.tail
+
+  // The empty AbbrevList.
+
+  case object AbbrevNil extends AbbrevList[Nothing]:
+    override def isEmpty = true
+
+    def head: Nothing =
+      throw NoSuchElementException("head of empty AbbrevList")
+
+    def tail: AbbrevList[Nothing] =
+      throw NoSuchElementException("tail of empty AbbrevList")
+
+  // A non-empty AbbrevList characterized by a head and a tail.
+
+  @targetName("AbbrevListCons")
+  final case class ::[B](private var hd: B,
+      private[list] var tl: AbbrevList[B]) extends AbbrevList[B]:
+
+    override def isEmpty: Boolean = false
+    def head : B = hd
+    def tail : AbbrevList[B] = tl

src/script/scala/progscala3/typesystem/bounds/list/ListAb.scala

@@ -1,5 +1,6 @@
 // src/script/scala/progscala3/typesystem/bounds/list/ListAb.scala
 import progscala3.typesystem.bounds.list.*
+import AbbrevListModule.*
 
 //val languages = AbbrevList("Scala", "Java", "Ruby", "C#", "C++", "Python")
 val languages: AbbrevList[String] =

src/test/scala/progscala3/typesystem/bounds/list/AbbrevListSuite.scala

@@ -1,6 +1,6 @@
 // src/test/scala/progscala3/typesystem/bounds/list/AbbrevListSuite.scala
 package progscala3.typesystem.bounds.list
-
+import AbbrevListModule.*
 import munit.*
 
 /**