SI-8549 Honour the @serialversionuid annotatation

In PR scala#1673 / 4267444, the annotation `SerialVersionId` was
changed from a `StaticAnnotation` to `ClassFileAnnotation` in
order to avoid silently ignoring non-literal UIDs like:

    @serialversionuid(0 - 12345L) class C

And to flag non-constant UIDs:

    @serialversionuid("!!!".length)

While this indeed was fold constants, the change was incomplete.
The compiler API for reading the argument from a `ClassFileAnnoation`
is different, on must look for a `LiteralAnnotArg`, rather than a
`Literal`.

This commit:

  - amends the backend accordingly
  - removes relevant duplication between `GenASM` and `GenBCode`
  - tests that the static field is generated accordingly

This will mean that we will break deserialization of objects from
Scalal 2.11.0 that use this annotation.

Author: retronym

src/compiler/scala/tools/nsc/backend/jvm/BCodeHelpers.scala

@@ -238,6 +238,13 @@ abstract class BCodeHelpers extends BCodeTypes with BytecodeWriters {
     cd.impl.body collect { case dd: DefDef => dd.symbol }
   }
 
+  /*
+   *  must-single-thread
+   */
+  def serialVUID(csym: Symbol): Option[Long] = csym getAnnotation definitions.SerialVersionUIDAttr collect {
+    case AnnotationInfo(_, _, (_, LiteralAnnotArg(const)) :: Nil) => const.longValue
+  }
+
   /*
    * Populates the InnerClasses JVM attribute with `refedInnerClasses`.
    * In addition to inner classes mentioned somewhere in `jclass` (where `jclass` is a class file being emitted)
@@ -880,13 +887,6 @@ abstract class BCodeHelpers extends BCodeTypes with BytecodeWriters {
     // The particular value in use for `MIN_SWITCH_DENSITY` reflects a heuristic.
     val MIN_SWITCH_DENSITY = 0.7
 
-    /*
-     *  must-single-thread
-     */
-    def serialVUID(csym: Symbol): Option[Long] = csym getAnnotation definitions.SerialVersionUIDAttr collect {
-      case AnnotationInfo(_, Literal(const) :: _, _) => const.longValue
-    }
-
     /*
      *  Add public static final field serialVersionUID with value `id`
      *

src/compiler/scala/tools/nsc/backend/jvm/GenASM.scala

@@ -1142,9 +1142,7 @@ abstract class GenASM extends SubComponent with BytecodeWriters with GenJVMASM {
 
     def isParcelableClass = isAndroidParcelableClass(clasz.symbol)
 
-    def serialVUID: Option[Long] = clasz.symbol getAnnotation SerialVersionUIDAttr collect {
-      case AnnotationInfo(_, Literal(const) :: _, _) => const.longValue
-    }
+    def serialVUID: Option[Long] = genBCode.serialVUID(clasz.symbol)
 
     private def getSuperInterfaces(c: IClass): Array[String] = {
 

test/files/run/t8549b.scala

@@ -0,0 +1,16 @@
+
+@SerialVersionUID(42)
+class C
+
+@SerialVersionUID(43 - 1)
+class D
+
+
+object Test extends App {
+  def checkId(cls: Class[_]) {
+    val id = cls.getDeclaredField("serialVersionUID").get(null)
+    assert(id == 42, (cls, id))  
+  }
+  checkId(classOf[C])
+  checkId(classOf[D])
+}