Only save UUID in classfile

Author: nicolasstucki

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

@@ -26,7 +26,7 @@ import scala.tools.asm
 import scala.tools.asm.tree._
 import tpd._
 import StdNames._
-import dotty.tools.dotc.core.tasty.TastyPickler
+import dotty.tools.dotc.core.tasty.{TastyBuffer, TastyHeaderUnpickler, TastyPickler}
 import dotty.tools.io._
 
 class GenBCode extends Phase {
@@ -222,9 +222,17 @@ class GenBCodePipeline(val entryPoints: List[Symbol], val int: DottyBackendInter
                 val outstream = new DataOutputStream(outTastyFile.bufferedOutput)
                 try outstream.write(binary)
                 finally outstream.close()
-                // TASTY attribute is created but only the header bytes are stored in it.
-                // A TASTY attribute has length `headerSize` if and only if the .tasty file exists.
-                java.util.Arrays.copyOf(binary, TastyPickler.headerSize)
+
+                val uuid = new TastyHeaderUnpickler(binary).readHeader()
+                val lo = uuid.getMostSignificantBits
+                val hi = uuid.getLeastSignificantBits
+
+                // TASTY attribute is created but only the UUID bytes are stored in it.
+                // A TASTY attribute has length 16 if and only if the .tasty file exists.
+                val buffer = new TastyBuffer(16)
+                buffer.writeUncompressedLong(lo)
+                buffer.writeUncompressedLong(hi)
+                buffer.bytes
               } else {
                 // Create an empty file to signal that a tasty section exist in the corresponding .class
                 // This is much cheaper and simpler to check than doing classfile parsing

compiler/src/dotty/tools/dotc/core/classfile/ClassfileParser.scala

@@ -5,15 +5,16 @@ package classfile
 
 import Contexts._, Symbols._, Types._, Names._, StdNames._, NameOps._, Scopes._, Decorators._
 import SymDenotations._, unpickleScala2.Scala2Unpickler._, Constants._, Annotations._, util.Positions._
-import NameKinds.{ModuleClassName, DefaultGetterName}
-import dotty.tools.dotc.core.tasty.{TastyHeaderUnpickler, TastyPickler}
+import NameKinds.DefaultGetterName
+import dotty.tools.dotc.core.tasty.{TastyHeaderUnpickler, TastyReader}
 import ast.tpd._
-import java.io.{ ByteArrayInputStream, ByteArrayOutputStream, DataInputStream, File, IOException }
-import java.nio
+import java.io.{ ByteArrayInputStream, ByteArrayOutputStream, DataInputStream, IOException }
+
 import java.lang.Integer.toHexString
 import java.net.URLClassLoader
+import java.util.UUID
 
-import scala.collection.{ mutable, immutable }
+import scala.collection.immutable
 import scala.collection.mutable.{ ListBuffer, ArrayBuffer }
 import scala.annotation.switch
 import typer.Checking.checkNonCyclic
@@ -787,9 +788,7 @@ class ClassfileParser(
       if (scan(tpnme.TASTYATTR)) {
         val attrLen = in.nextInt
         val bytes = in.nextBytes(attrLen)
-        val headerUnpickler = new TastyHeaderUnpickler(bytes)
-        headerUnpickler.readHeader()
-        if (headerUnpickler.isAtEnd) { // A tasty attribute with that has only a header implies the existence of the .tasty file
+        if (bytes.length == 16) { // A tasty attribute with that has only a UUID implies the existence of the .tasty file
           val tastyBytes: Array[Byte] = classfile.underlyingSource match { // TODO: simplify when #3552 is fixed
             case None =>
               ctx.error("Could not load TASTY from .tasty for virtual file " + classfile)
@@ -821,8 +820,11 @@ class ClassfileParser(
               }
           }
           if (tastyBytes.nonEmpty) {
-            if (!tastyBytes.startsWith(bytes))
-              ctx.error("Header of TASTY file did not correspond to header in classfile. One of the files might be outdated or corrupted.")
+            val reader = new TastyReader(bytes, 0, 16)
+            val expectedUUID = new UUID(reader.readUncompressedLong(), reader.readUncompressedLong())
+            val tastyUUID = new TastyHeaderUnpickler(tastyBytes).readHeader()
+            if (expectedUUID != tastyUUID)
+              ctx.error(s"Tasty UUID ($tastyUUID) file did not correspond the tasty UUID declared in the classfile ($expectedUUID).")
             return unpickleTASTY(tastyBytes)
           }
         }

compiler/src/dotty/tools/dotc/core/tasty/TastyPickler.scala

@@ -29,13 +29,12 @@ class TastyPickler(val rootCls: ClassSymbol) {
     val uuidHi: Long = sections.iterator.map(x => pjwHash64(x._2.bytes)).fold(0L)(_ ^ _)
 
     val headerBuffer = {
-      val buf = new TastyBuffer(TastyPickler.headerSize)
+      val buf = new TastyBuffer(header.length + 24)
       for (ch <- header) buf.writeByte(ch.toByte)
       buf.writeNat(MajorVersion)
       buf.writeNat(MinorVersion)
       buf.writeUncompressedLong(uuidLow)
       buf.writeUncompressedLong(uuidHi)
-      assert(buf.length == TastyPickler.headerSize)
       buf
     }
 
@@ -91,7 +90,3 @@ class TastyPickler(val rootCls: ClassSymbol) {
     h
   }
 }
-
-object TastyPickler {
-  val headerSize = header.length + 18
-}