Accommodate Scala 2 annotation value

Author: som-snytt

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

@@ -38,7 +38,7 @@ object Annotations {
       if (i < args.length) Some(args(i)) else None
     }
     def argumentConstant(i: Int)(using Context): Option[Constant] =
-      for (case ConstantType(c) <- argument(i) map (_.tpe.widenTermRefExpr.normalized)) yield c
+      for case ConstantType(c) <- argument(i).map(stripCast(_).tpe.widenTermRefExpr.normalized) yield c
 
     def argumentConstantString(i: Int)(using Context): Option[String] =
       for (case Constant(s: String) <- argumentConstant(i)) yield s

tests/neg/serialversionuid-not-const.scala

@@ -1,6 +1,6 @@
 @SerialVersionUID(13l.toLong) class C1 extends Serializable // OK because toLong is constant-folded
 @SerialVersionUID(13l) class C2 extends Serializable // OK
-@SerialVersionUID(13.asInstanceOf[Long]) class C3 extends Serializable // error
+@SerialVersionUID(13.asInstanceOf[Long]) class C3 extends Serializable // OK was error
 @SerialVersionUID(Test.bippy) class C4 extends Serializable // error
 
 object Test {