Avoid initializing Product and Serializable too early

This lead to crashes in the full bootstrap and doesn't seem necessary in
any case.

Author: smarter

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

@@ -1391,13 +1391,6 @@ class Definitions {
       for (m <- ScalaShadowingPackageClass.info.decls)
         ScalaPackageClass.enter(m)
 
-      // Temporary measure, as long as we do not read these classes from Tasty.
-      // Scala-2 classes don't have NoInits set even if they are pure. We override this
-      // for Product and Serializable so that case classes can be pure. A full solution
-      // requires that we read all Scala code from Tasty.
-      ProductClass.setFlag(NoInits)
-      SerializableClass.setFlag(NoInits)
-
       // force initialization of every symbol that is synthesized or hijacked by the compiler
       val forced = syntheticCoreClasses ++ syntheticCoreMethods ++ ScalaValueClasses()
 

compiler/src/dotty/tools/dotc/core/unpickleScala2/Scala2Unpickler.scala

@@ -467,6 +467,14 @@ class Scala2Unpickler(bytes: Array[Byte], classRoot: ClassDenotation, moduleClas
     def completeRoot(denot: ClassDenotation, completer: LazyType): Symbol = {
       denot.setFlag(flags)
       denot.resetFlag(Touched) // allow one more completion
+
+      // Temporary measure, as long as we do not read these classes from Tasty.
+      // Scala-2 classes don't have NoInits set even if they are pure. We override this
+      // for Product and Serializable so that case classes can be pure. A full solution
+      // requires that we read all Scala code from Tasty.
+      if (owner == defn.ScalaPackageClass && ((name eq nme.Serializable) || (name eq nme.Product)))
+        denot.setFlag(NoInits)
+
       denot.info = completer
       denot.symbol
     }