Upgrade to ASM 7.0

Catch up with Scala 2.13.

The corresponding scalac PRs are
scala/scala#6733 and
scala/scala#7384

Most of the changes from these PRs aren't currently needed in Dotty
since they only affect the Scala 2 backend optimizer.

Author: smarter

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

@@ -3,6 +3,7 @@ package backend
 package jvm
 
 import scala.tools.asm
+import scala.tools.asm.ClassWriter
 import scala.collection.mutable
 import dotty.tools.io.AbstractFile
 
@@ -126,6 +127,20 @@ trait BCodeHelpers extends BCodeIdiomatic with BytecodeWriters {
     }
   }
 
+  /*
+   * can-multi-thread
+   */
+  def createJAttribute(name: String, b: Array[Byte], offset: Int, len: Int): asm.Attribute = {
+    new asm.Attribute(name) {
+      override def write(classWriter: ClassWriter, code: Array[Byte],
+        codeLength: Int, maxStack: Int, maxLocals: Int): asm.ByteVector = {
+        val byteVector = new asm.ByteVector(len)
+        byteVector.putByteArray(b, offset, len)
+        byteVector
+      }
+    }
+  }
+
   /*
    * Custom attribute (JVMS 4.7.1) "ScalaSig" used as marker only
    * i.e., the pickle is contained in a custom annotation, see:
@@ -151,15 +166,6 @@ trait BCodeHelpers extends BCodeIdiomatic with BytecodeWriters {
       vp
     }
 
-    /*
-     * can-multi-thread
-     */
-    def createJAttribute(name: String, b: Array[Byte], offset: Int, len: Int): asm.Attribute = {
-      val dest = new Array[Byte](len)
-      System.arraycopy(b, offset, dest, 0, len)
-      new asm.CustomAttr(name, dest)
-    }
-
     /*
      * can-multi-thread
      */

compiler/src/dotty/tools/backend/jvm/GenBCode.scala

@@ -7,7 +7,6 @@ import dotty.tools.dotc.core.Phases.Phase
 
 import scala.collection.mutable
 import scala.collection.JavaConverters._
-import scala.tools.asm.CustomAttr
 import dotty.tools.dotc.transform.SymUtils._
 import dotty.tools.dotc.interfaces
 import dotty.tools.dotc.util.SourceFile
@@ -240,7 +239,7 @@ class GenBCodePipeline(val entryPoints: List[Symbol], val int: DottyBackendInter
                 getFileForClassfile(outF, store.name, ".hasTasty")
                 binary
               }
-            val dataAttr = new CustomAttr(nme.TASTYATTR.mangledString, tasty)
+            val dataAttr = createJAttribute(nme.TASTYATTR.mangledString, tasty, 0, tasty.size)
             store.visitAttribute(dataAttr)
           }
 

project/Build.scala

@@ -481,7 +481,7 @@ object Build {
 
       // get libraries onboard
       libraryDependencies ++= Seq(
-        "org.scala-lang.modules" % "scala-asm" % "6.0.0-scala-1", // used by the backend
+        "org.scala-lang.modules" % "scala-asm" % "7.0.0-scala-1", // used by the backend
         // FIXME: Not needed, but should be on the compiler CP
         ("org.scala-lang.modules" %% "scala-xml" % "1.1.0").withDottyCompat(scalaVersion.value),
         "org.scala-lang" % "scala-library" % scalacVersion % "test",