SI-8679 Add support for ScalaLongSignature attribute in scalap

scalap didn't support really big class files. It was returning an
empty String for such files. The reason was that there were only
ScalaSignatures taken into account.

This commit adds support for ScalaLongSignature. We try to get such
an attribute when we didn't find ScalaSignature. Also there's added
an additional case to the logic retrieving bytes for a signature.
Since ScalaLongSignature can contain many parts, we have to merge
their byte arrays.

Changes are tested by a new partest-based test. These two files are
really big, but it was required (t8679.scala is a reduced version of
BigScalaClass - an example attached to JIRA).

There are also added TODOs with a JIRA ticket: We have three places,
where we process Scala signatures. In the future it would be better to
reuse some common logic, if it's possible.

Author: mpociecha

src/compiler/scala/tools/nsc/symtab/classfile/ClassfileParser.scala

@@ -923,6 +923,7 @@ abstract class ClassfileParser {
       Some(ScalaSigBytes(pool.getBytes(entries.toList)))
     }
 
+    // TODO SI-9296 duplicated code, refactor
     /* Parse and return a single annotation.  If it is malformed,
      * return None.
      */

src/reflect/scala/reflect/runtime/JavaMirrors.scala

@@ -591,6 +591,7 @@ private[scala] trait JavaMirrors extends internal.SymbolTable with api.JavaUnive
       // don't use classOf[scala.reflect.ScalaSignature] here, because it will use getClass.getClassLoader, not mirror's classLoader
       // don't use asInstanceOf either because of the same reason (lol, I cannot believe I fell for it)
       // don't use structural types to simplify reflective invocations because of the same reason
+      // TODO SI-9296 duplicated code, refactor
       def loadAnnotation(name: String): Option[java.lang.annotation.Annotation] =
         tryJavaClass(name) flatMap { annotClass =>
           val anns = jclazz.getAnnotations

src/scalap/scala/tools/scalap/Main.scala

@@ -28,6 +28,7 @@ import scalax.rules.scalasig._
 class Main {
   val SCALA_SIG            = "ScalaSig"
   val SCALA_SIG_ANNOTATION = "Lscala/reflect/ScalaSignature;"
+  val SCALA_LONG_SIG_ANNOTATION = "Lscala/reflect/ScalaLongSignature;"
   val BYTES_VALUE          = "bytes"
 
   val versionMsg = "Scala classfile decoder %s -- %s\n".format(Properties.versionString, Properties.copyrightString)

src/scalap/scala/tools/scalap/scalax/rules/scalasig/ScalaSig.scala

@@ -14,20 +14,32 @@ package scalasig
 import scala.language.postfixOps
 import scala.language.implicitConversions
 
-import ClassFileParser.{ ConstValueIndex, Annotation }
+import ClassFileParser._
 import scala.reflect.internal.pickling.ByteCodecs
 
 object ScalaSigParser {
-  import Main.{ SCALA_SIG, SCALA_SIG_ANNOTATION, BYTES_VALUE }
+  import Main.{ BYTES_VALUE, SCALA_LONG_SIG_ANNOTATION, SCALA_SIG, SCALA_SIG_ANNOTATION }
 
+  // TODO SI-9296 duplicated code, refactor
   def scalaSigFromAnnotation(classFile: ClassFile): Option[ScalaSig] = {
     import classFile._
 
-    classFile.annotation(SCALA_SIG_ANNOTATION) map {
+    def getBytes(bytesElem: AnnotationElement): Array[Byte] = bytesElem.elementValue match {
+      case ConstValueIndex(index) => bytesForIndex(index)
+      case ArrayValue(signatureParts) => mergedLongSignatureBytes(signatureParts)
+    }
+
+    def mergedLongSignatureBytes(signatureParts: Seq[ElementValue]): Array[Byte] = signatureParts.flatMap {
+      case ConstValueIndex(index) => bytesForIndex(index)
+    }(collection.breakOut)
+
+    def bytesForIndex(index: Int) = constantWrapped(index).asInstanceOf[StringBytesPair].bytes
+
+    classFile.annotation(SCALA_SIG_ANNOTATION)
+      .orElse(classFile.annotation(SCALA_LONG_SIG_ANNOTATION)).map {
       case Annotation(_, elements) =>
         val bytesElem = elements.find(elem => constant(elem.elementNameIndex) == BYTES_VALUE).get
-        val bytes = ((bytesElem.elementValue match {case ConstValueIndex(index) => constantWrapped(index)})
-                .asInstanceOf[StringBytesPair].bytes)
+        val bytes = getBytes(bytesElem)
         val length = ByteCodecs.decode(bytes)
 
         ScalaSigAttributeParsers.parse(ByteCode(bytes.take(length)))