Add desugared version for enum.scala

Author: EnzeXing

tests/init/neg/enum-desugared.check

@@ -0,0 +1,18 @@
+-- Error: tests/init/neg/enum-desugared.scala:17:15 --------------------------------------------------------------------
+17 |    Array(this.LazyErrorId, this.NoExplanationID) // error // error
+   |          ^^^^^^^^^^^^^^^^
+   |          Promoting the value to fully-initialized is unsafe. May only use initialized value as method arguments
+   |
+   |          The unsafe promotion may cause the following problem(s):
+   |
+   |          1. Calling the external method method name may cause initialization errors. Calling trace:
+   |           -> override def productPrefix: String = this.name()	[ enum-desugared.scala:29 ]
+-- Error: tests/init/neg/enum-desugared.scala:17:33 --------------------------------------------------------------------
+17 |    Array(this.LazyErrorId, this.NoExplanationID) // error // error
+   |                            ^^^^^^^^^^^^^^^^^^^^
+   |          Promoting the value to fully-initialized is unsafe. May only use initialized value as method arguments
+   |
+   |          The unsafe promotion may cause the following problem(s):
+   |
+   |          1. Calling the external method method ordinal may cause initialization errors. Calling trace:
+   |           -> def errorNumber: Int = this.ordinal() - 2	[ enum-desugared.scala:8 ]

tests/init/neg/enum-desugared.scala

@@ -0,0 +1,35 @@
+package example
+
+import language.`3.0-migration`
+
+sealed abstract class ErrorMessageID($name: String, _$ordinal: Int)
+  extends java.lang.Enum[ErrorMessageID]($name, _$ordinal) with scala.reflect.Enum {
+
+  def errorNumber: Int = this.ordinal() - 2
+}
+
+object ErrorMessageID {
+
+  final val LazyErrorId = $new(0, "LazyErrorId")
+  final val NoExplanationID = $new(1, "NoExplanationID")
+
+  private[this] val $values: Array[ErrorMessageID] =
+    Array(this.LazyErrorId, this.NoExplanationID) // error // error
+
+  def values: Array[ErrorMessageID] = $values.clone()
+
+  def valueOf($name: String): ErrorMessageID = $name match {
+    case "LazyErrorId" => this.LazyErrorId
+    case "NoExplanationID" => this.NoExplanationID
+    case _ => throw new IllegalArgumentException("enum case not found: " + $name)
+  }
+
+  private[this] def $new(_$ordinal: Int, $name: String): ErrorMessageID =
+    new ErrorMessageID($name, _$ordinal) with scala.runtime.EnumValue {
+        override def productPrefix: String = this.name()
+    }
+
+  def fromOrdinal(ordinal: Int): ErrorMessageID =
+    try ErrorMessageID.$values.apply(ordinal)
+    catch { case _ => throw new NoSuchElementException(ordinal.toString()) }
+}

tests/init/pos/methodAtLast.scala

@@ -0,0 +1,11 @@
+class Foo(x: Int) {
+    var y: Int = x
+    case class Bar(z: Int) extends Foo(z)
+    def updateY(n: Int): Unit = {
+        if (y < 20) {
+            val b = new Bar(x + n)
+            y = b.z
+        }
+    }
+    updateY(5)
+}