Prioritize TASTy files over classfiles on classpath aggregation

In most cases the TASTy file is chosen over the classfile in a classpath
because they are packaged together. However, for the `scala-library`
(Scala 2 compiled library) and `scala2-library-tasty` (Scala 3 compiled Scala 2 library)
we have the classfiles in one jar and the TASTy files in another jar.
Given that the classpaths order in guaranteed to be deterministic we might
end up with the classfile being loaded first and the TASTy file second.
The aggregator must be capable of choosing the TASTy file over the classfile
in this case as well. The aggregator will only choose the new TASTy over
the old classfile if the TASTy file has no classfile in its classpath. In
other words, we only use this new behaviour for TASTy only classpaths.

This also implies that we can just add the `scala2-library-tasty` as a
dependency in any project to use it. Note that this jar is not published
yet.

compiler/src/dotty/tools/dotc/classpath/AggregateClassPath.scala

@@ -39,14 +39,14 @@ case class AggregateClassPath(aggregates: Seq[ClassPath]) extends ClassPath {
     def findEntry(isSource: Boolean): Option[ClassRepresentation] =
       aggregatesForPackage(PackageName(pkg)).iterator.map(_.findClass(className)).collectFirst {
         case Some(s: SourceFileEntry) if isSource => s
-        case Some(s: ClassFileEntry) if !isSource => s
+        case Some(s: BinaryFileEntry) if !isSource => s
       }
 
     val classEntry = findEntry(isSource = false)
     val sourceEntry = findEntry(isSource = true)
 
     (classEntry, sourceEntry) match {
-      case (Some(c: ClassFileEntry), Some(s: SourceFileEntry)) => Some(ClassAndSourceFilesEntry(c.file, s.file))
+      case (Some(c: BinaryFileEntry), Some(s: SourceFileEntry)) => Some(BinaryAndSourceFilesEntry(c, s))
       case (c @ Some(_), _) => c
       case (_, s) => s
     }
@@ -63,7 +63,7 @@ case class AggregateClassPath(aggregates: Seq[ClassPath]) extends ClassPath {
     aggregatedPackages
   }
 
-  override private[dotty] def classes(inPackage: PackageName): Seq[ClassFileEntry] =
+  override private[dotty] def classes(inPackage: PackageName): Seq[BinaryFileEntry] =
     getDistinctEntries(_.classes(inPackage))
 
   override private[dotty] def sources(inPackage: PackageName): Seq[SourceFileEntry] =
@@ -102,10 +102,17 @@ case class AggregateClassPath(aggregates: Seq[ClassPath]) extends ClassPath {
     ClassPathEntries(distinctPackages, distinctClassesAndSources)
   }
 
-  /**
-   * Returns only one entry for each name. If there's both a source and a class entry, it
-   * creates an entry containing both of them. If there would be more than one class or source
-   * entries for the same class it always would use the first entry of each type found on a classpath.
+  /** Returns only one entry for each name.
+   *
+   *  If there's both a source and a class entry, it
+   *  creates an entry containing both of them. If there would be more than one class or source
+   *  entries for the same class it always would use the first entry of each type found on a classpath.
+   *
+   *  A class entry with a TASTy file will be chosen over one with a class file. Usually the class entries
+   *  are already TASTy files when loading Scala 3 classes because the other classpath loaders load the TASTy.
+   *  There is one exception if we load the Scala 2 library as it has one JAR containing the class files and one
+   *  JAR containing the TASTy files. As classpath orders are not guaranteed to be deterministic we might end up
+   *  having the TASTy in a later classpath entry.
    */
   private def mergeClassesAndSources(entries: scala.collection.Seq[ClassRepresentation]): Seq[ClassRepresentation] = {
     // based on the implementation from MergedClassPath
@@ -119,11 +126,18 @@ case class AggregateClassPath(aggregates: Seq[ClassPath]) extends ClassPath {
       if (indices.contains(name)) {
         val index = indices(name)
         val existing = mergedEntries(index)
-
-        if (existing.binary.isEmpty && entry.binary.isDefined)
-          mergedEntries(index) = ClassAndSourceFilesEntry(entry.binary.get, existing.source.get)
-        if (existing.source.isEmpty && entry.source.isDefined)
-          mergedEntries(index) = ClassAndSourceFilesEntry(existing.binary.get, entry.source.get)
+        (entry, existing) match
+          case (entry: SourceFileEntry, existing: BinaryFileEntry) =>
+            mergedEntries(index) = BinaryAndSourceFilesEntry(existing, entry)
+          case (entry: BinaryFileEntry, existing: SourceFileEntry) =>
+            mergedEntries(index) = BinaryAndSourceFilesEntry(entry, existing)
+          case (entry: StandaloneTastyFileEntry, _: ClassFileEntry) =>
+            // Here we do not create a TastyFileEntry(entry.file) because the TASTy and the classfile
+            // come from different classpaths. These may not have the same TASTy UUID.
+            mergedEntries(index) = entry
+          case (entry: StandaloneTastyFileEntry, BinaryAndSourceFilesEntry(_: ClassFileEntry, sourceEntry)) =>
+            mergedEntries(index) = BinaryAndSourceFilesEntry(entry, sourceEntry)
+          case _ =>
       }
       else {
         indices(name) = count

compiler/src/dotty/tools/dotc/classpath/ClassPath.scala

@@ -3,6 +3,7 @@
  */
 package dotty.tools.dotc.classpath
 
+import dotty.tools.dotc.classpath.FileUtils.isTasty
 import dotty.tools.io.AbstractFile
 import dotty.tools.io.ClassRepresentation
 
@@ -14,14 +15,6 @@ object ClassPathEntries {
   val empty = ClassPathEntries(Seq.empty, Seq.empty)
 }
 
-trait ClassFileEntry extends ClassRepresentation {
-  def file: AbstractFile
-}
-
-trait SourceFileEntry extends ClassRepresentation {
-  def file: AbstractFile
-}
-
 case class PackageName(dottedString: String) {
   val dirPathTrailingSlashJar: String = FileUtils.dirPathInJar(dottedString) + "/"
 
@@ -48,28 +41,50 @@ trait PackageEntry {
   def name: String
 }
 
-private[dotty] case class ClassFileEntryImpl(file: AbstractFile) extends ClassFileEntry {
+/** A TASTy file or classfile */
+sealed trait BinaryFileEntry extends ClassRepresentation {
+  def file: AbstractFile
   final def fileName: String = file.name
-  def name: String = FileUtils.stripClassExtension(file.name) // class name
+  final def name: String = FileUtils.stripClassExtension(file.name) // class name
+  final def source: Option[AbstractFile] = None
+}
 
+object BinaryFileEntry {
+  def apply(file: AbstractFile): BinaryFileEntry =
+    if file.isTasty then
+      if file.resolveSiblingWithExtension("class") != null then TastyFileEntry(file)
+      else StandaloneTastyFileEntry(file)
+    else
+      ClassFileEntry(file)
+}
+
+/** A classfile or .sig that does not have an associated TASTy file */
+private[dotty] final case class ClassFileEntry(file: AbstractFile) extends BinaryFileEntry {
   def binary: Option[AbstractFile] = Some(file)
-  def source: Option[AbstractFile] = None
 }
 
-private[dotty] case class SourceFileEntryImpl(file: AbstractFile) extends SourceFileEntry {
+/** A TASTy file that has an associated TASTy */
+private[dotty] final case class TastyFileEntry(file: AbstractFile) extends BinaryFileEntry {
+  def binary: Option[AbstractFile] = Some(file)
+}
+
+/** A TASTy file that does not have an associated TASTy */
+private[dotty] final case class StandaloneTastyFileEntry(file: AbstractFile) extends BinaryFileEntry {
+  def binary: Option[AbstractFile] = Some(file)
+}
+
+private[dotty] final case class SourceFileEntry(file: AbstractFile) extends ClassRepresentation {
   final def fileName: String = file.name
   def name: String = FileUtils.stripSourceExtension(file.name)
-
   def binary: Option[AbstractFile] = None
   def source: Option[AbstractFile] = Some(file)
 }
 
-private[dotty] case class ClassAndSourceFilesEntry(classFile: AbstractFile, srcFile: AbstractFile) extends ClassRepresentation {
-  final def fileName: String = classFile.name
-  def name: String = FileUtils.stripClassExtension(classFile.name)
-
-  def binary: Option[AbstractFile] = Some(classFile)
-  def source: Option[AbstractFile] = Some(srcFile)
+private[dotty] final case class BinaryAndSourceFilesEntry(binaryEntry: BinaryFileEntry, sourceEntry: SourceFileEntry) extends ClassRepresentation {
+  final def fileName: String = binaryEntry.fileName
+  def name: String = binaryEntry.name
+  def binary: Option[AbstractFile] = binaryEntry.binary
+  def source: Option[AbstractFile] = sourceEntry.source
 }
 
 private[dotty] case class PackageEntryImpl(name: String) extends PackageEntry
@@ -81,5 +96,5 @@ private[dotty] trait NoSourcePaths {
 
 private[dotty] trait NoClassPaths {
   def findClassFile(className: String): Option[AbstractFile] = None
-  private[dotty] def classes(inPackage: PackageName): Seq[ClassFileEntry] = Seq.empty
+  private[dotty] def classes(inPackage: PackageName): Seq[BinaryFileEntry] = Seq.empty
 }

compiler/src/dotty/tools/dotc/classpath/DirectoryClassPath.scala

@@ -183,12 +183,12 @@ final class JrtClassPath(fs: java.nio.file.FileSystem) extends ClassPath with No
   override private[dotty] def packages(inPackage: PackageName): Seq[PackageEntry] =
     packageToModuleBases.keysIterator.filter(pack => packageContains(inPackage.dottedString, pack)).map(PackageEntryImpl(_)).toVector
 
-  private[dotty] def classes(inPackage: PackageName): Seq[ClassFileEntry] =
+  private[dotty] def classes(inPackage: PackageName): Seq[BinaryFileEntry] =
     if (inPackage.isRoot) Nil
     else
       packageToModuleBases.getOrElse(inPackage.dottedString, Nil).flatMap(x =>
         Files.list(x.resolve(inPackage.dirPathTrailingSlash)).iterator().asScala.filter(_.getFileName.toString.endsWith(".class"))).map(x =>
-        ClassFileEntryImpl(x.toPlainFile)).toVector
+        ClassFileEntry(x.toPlainFile)).toVector
 
   override private[dotty] def list(inPackage: PackageName): ClassPathEntries =
     if (inPackage.isRoot) ClassPathEntries(packages(inPackage), Nil)
@@ -246,12 +246,12 @@ final class CtSymClassPath(ctSym: java.nio.file.Path, release: Int) extends Clas
   override private[dotty] def packages(inPackage: PackageName): Seq[PackageEntry] = {
     packageIndex.keysIterator.filter(pack => packageContains(inPackage.dottedString, pack)).map(PackageEntryImpl(_)).toVector
   }
-  private[dotty] def classes(inPackage: PackageName): Seq[ClassFileEntry] = {
+  private[dotty] def classes(inPackage: PackageName): Seq[BinaryFileEntry] = {
     if (inPackage.isRoot) Nil
     else {
       val sigFiles = packageIndex.getOrElse(inPackage.dottedString, Nil).iterator.flatMap(p =>
         Files.list(p).iterator.asScala.filter(_.getFileName.toString.endsWith(".sig")))
-      sigFiles.map(f => ClassFileEntryImpl(f.toPlainFile)).toVector
+      sigFiles.map(f => ClassFileEntry(f.toPlainFile)).toVector
     }
   }
 
@@ -273,33 +273,35 @@ final class CtSymClassPath(ctSym: java.nio.file.Path, release: Int) extends Clas
   }
 }
 
-case class DirectoryClassPath(dir: JFile) extends JFileDirectoryLookup[ClassFileEntryImpl] with NoSourcePaths {
-  override def findClass(className: String): Option[ClassRepresentation] = findClassFile(className) map ClassFileEntryImpl.apply
+case class DirectoryClassPath(dir: JFile) extends JFileDirectoryLookup[BinaryFileEntry] with NoSourcePaths {
+  override def findClass(className: String): Option[ClassRepresentation] =
+    findClassFile(className).map(BinaryFileEntry(_))
 
   def findClassFile(className: String): Option[AbstractFile] = {
     val relativePath = FileUtils.dirPath(className)
     val tastyFile = new JFile(dir, relativePath + ".tasty")
     if tastyFile.exists then Some(tastyFile.toPath.toPlainFile)
     else
       val classFile = new JFile(dir, relativePath + ".class")
-      if classFile.exists then  Some(classFile.toPath.toPlainFile)
+      if classFile.exists then Some(classFile.toPath.toPlainFile)
       else None
   }
 
-  protected def createFileEntry(file: AbstractFile): ClassFileEntryImpl = ClassFileEntryImpl(file)
+  protected def createFileEntry(file: AbstractFile): BinaryFileEntry = BinaryFileEntry(file)
+
   protected def isMatchingFile(f: JFile): Boolean =
     f.isTasty || (f.isClass && f.classToTasty.isEmpty)
 
-  private[dotty] def classes(inPackage: PackageName): Seq[ClassFileEntry] = files(inPackage)
+  private[dotty] def classes(inPackage: PackageName): Seq[BinaryFileEntry] = files(inPackage)
 }
 
-case class DirectorySourcePath(dir: JFile) extends JFileDirectoryLookup[SourceFileEntryImpl] with NoClassPaths {
+case class DirectorySourcePath(dir: JFile) extends JFileDirectoryLookup[SourceFileEntry] with NoClassPaths {
   def asSourcePathString: String = asClassPathString
 
-  protected def createFileEntry(file: AbstractFile): SourceFileEntryImpl = SourceFileEntryImpl(file)
+  protected def createFileEntry(file: AbstractFile): SourceFileEntry = SourceFileEntry(file)
   protected def isMatchingFile(f: JFile): Boolean = endsScalaOrJava(f.getName)
 
-  override def findClass(className: String): Option[ClassRepresentation] = findSourceFile(className) map SourceFileEntryImpl.apply
+  override def findClass(className: String): Option[ClassRepresentation] = findSourceFile(className).map(SourceFileEntry(_))
 
   private def findSourceFile(className: String): Option[AbstractFile] = {
     val relativePath = FileUtils.dirPath(className)

compiler/src/dotty/tools/dotc/classpath/VirtualDirectoryClassPath.scala

@@ -7,7 +7,7 @@ import dotty.tools.io.{AbstractFile, VirtualDirectory}
 import FileUtils.*
 import java.net.{URI, URL}
 
-case class VirtualDirectoryClassPath(dir: VirtualDirectory) extends ClassPath with DirectoryLookup[ClassFileEntryImpl] with NoSourcePaths {
+case class VirtualDirectoryClassPath(dir: VirtualDirectory) extends ClassPath with DirectoryLookup[BinaryFileEntry] with NoSourcePaths {
   type F = AbstractFile
 
   // From AbstractFileClassLoader
@@ -38,7 +38,8 @@ case class VirtualDirectoryClassPath(dir: VirtualDirectory) extends ClassPath wi
   def asURLs: Seq[URL] = Seq(new URI(dir.name).toURL)
   def asClassPathStrings: Seq[String] = Seq(dir.path)
 
-  override def findClass(className: String): Option[ClassRepresentation] = findClassFile(className) map ClassFileEntryImpl.apply
+  override def findClass(className: String): Option[ClassRepresentation] =
+    findClassFile(className).map(BinaryFileEntry(_))
 
   def findClassFile(className: String): Option[AbstractFile] = {
     val pathSeq = FileUtils.dirPath(className).split(java.io.File.separator)
@@ -49,9 +50,10 @@ case class VirtualDirectoryClassPath(dir: VirtualDirectory) extends ClassPath wi
         .orElse(Option(lookupPath(parentDir)(pathSeq.last + ".class" :: Nil, directory = false)))
   }
 
-  private[dotty] def classes(inPackage: PackageName): Seq[ClassFileEntry] = files(inPackage)
+  private[dotty] def classes(inPackage: PackageName): Seq[BinaryFileEntry] = files(inPackage)
+
+  protected def createFileEntry(file: AbstractFile): BinaryFileEntry = BinaryFileEntry(file)
 
-  protected def createFileEntry(file: AbstractFile): ClassFileEntryImpl = ClassFileEntryImpl(file)
   protected def isMatchingFile(f: AbstractFile): Boolean =
     f.isTasty || (f.isClass && f.classToTasty.isEmpty)
 }

compiler/src/dotty/tools/dotc/classpath/ZipAndJarFileLookupFactory.scala

@@ -41,22 +41,23 @@ sealed trait ZipAndJarFileLookupFactory {
  */
 object ZipAndJarClassPathFactory extends ZipAndJarFileLookupFactory {
   private case class ZipArchiveClassPath(zipFile: File, override val release: Option[String])
-    extends ZipArchiveFileLookup[ClassFileEntryImpl]
+    extends ZipArchiveFileLookup[BinaryFileEntry]
     with NoSourcePaths {
 
     override def findClassFile(className: String): Option[AbstractFile] =
       findClass(className).map(_.file)
 
     // This method is performance sensitive as it is used by SBT's ExtractDependencies phase.
-    override def findClass(className: String): Option[ClassFileEntryImpl] = {
+    override def findClass(className: String): Option[BinaryFileEntry] = {
       val (pkg, simpleClassName) = PackageNameUtils.separatePkgAndClassNames(className)
       val binaries = files(PackageName(pkg), simpleClassName + ".tasty", simpleClassName + ".class")
       binaries.find(_.file.isTasty).orElse(binaries.find(_.file.isClass))
     }
 
-    override private[dotty] def classes(inPackage: PackageName): Seq[ClassFileEntry] = files(inPackage)
+    override private[dotty] def classes(inPackage: PackageName): Seq[BinaryFileEntry] = files(inPackage)
+
+    override protected def createFileEntry(file: FileZipArchive#Entry): BinaryFileEntry = BinaryFileEntry(file)
 
-    override protected def createFileEntry(file: FileZipArchive#Entry): ClassFileEntryImpl = ClassFileEntryImpl(file)
     override protected def isRequiredFileType(file: AbstractFile): Boolean =
       file.isTasty || (file.isClass && file.classToTasty.isEmpty)
   }
@@ -128,10 +129,10 @@ object ZipAndJarClassPathFactory extends ZipAndJarFileLookupFactory {
         subpackages.map(packageFile => PackageEntryImpl(inPackage.entryName(packageFile.name)))
     }
 
-    override private[dotty] def classes(inPackage: PackageName): Seq[ClassFileEntry] = cachedPackages.get(inPackage.dottedString) match {
+    override private[dotty] def classes(inPackage: PackageName): Seq[BinaryFileEntry] = cachedPackages.get(inPackage.dottedString) match {
       case None => Seq.empty
       case Some(PackageFileInfo(pkg, _)) =>
-        (for (file <- pkg if file.isClass) yield ClassFileEntryImpl(file)).toSeq
+        (for (file <- pkg if file.isClass) yield ClassFileEntry(file)).toSeq
     }
 
     override private[dotty] def hasPackage(pkg: PackageName) = cachedPackages.contains(pkg.dottedString)
@@ -162,7 +163,7 @@ object ZipAndJarClassPathFactory extends ZipAndJarFileLookupFactory {
  */
 object ZipAndJarSourcePathFactory extends ZipAndJarFileLookupFactory {
   private case class ZipArchiveSourcePath(zipFile: File)
-    extends ZipArchiveFileLookup[SourceFileEntryImpl]
+    extends ZipArchiveFileLookup[SourceFileEntry]
     with NoClassPaths {
 
     def release: Option[String] = None
@@ -171,7 +172,7 @@ object ZipAndJarSourcePathFactory extends ZipAndJarFileLookupFactory {
 
     override private[dotty] def sources(inPackage: PackageName): Seq[SourceFileEntry] = files(inPackage)
 
-    override protected def createFileEntry(file: FileZipArchive#Entry): SourceFileEntryImpl = SourceFileEntryImpl(file)
+    override protected def createFileEntry(file: FileZipArchive#Entry): SourceFileEntry = SourceFileEntry(file)
     override protected def isRequiredFileType(file: AbstractFile): Boolean = file.isScalaOrJavaSource
   }
 

compiler/src/dotty/tools/io/AbstractFile.scala

@@ -258,6 +258,9 @@ abstract class AbstractFile extends Iterable[AbstractFile] {
   final def resolveSibling(name: String): AbstractFile | Null =
     container.lookupName(name, directory = false)
 
+  final def resolveSiblingWithExtension(extension: String): AbstractFile | Null =
+    resolveSibling(name.stripSuffix(this.extension) + extension)
+
   private def fileOrSubdirectoryNamed(name: String, isDir: Boolean): AbstractFile =
     lookupName(name, isDir) match {
       case null =>

compiler/src/dotty/tools/io/ClassPath.scala

@@ -26,7 +26,7 @@ trait ClassPath {
 
   final def hasPackage(pkg: String): Boolean = hasPackage(PackageName(pkg))
   final def packages(inPackage: String): Seq[PackageEntry] = packages(PackageName(inPackage))
-  final def classes(inPackage: String): Seq[ClassFileEntry] = classes(PackageName(inPackage))
+  final def classes(inPackage: String): Seq[BinaryFileEntry] = classes(PackageName(inPackage))
   final def sources(inPackage: String): Seq[SourceFileEntry] = sources(PackageName(inPackage))
   final def list(inPackage: String): ClassPathEntries = list(PackageName(inPackage))
 
@@ -43,7 +43,7 @@ trait ClassPath {
 
   private[dotty] def hasPackage(pkg: PackageName): Boolean
   private[dotty] def packages(inPackage: PackageName): Seq[PackageEntry]
-  private[dotty] def classes(inPackage: PackageName): Seq[ClassFileEntry]
+  private[dotty] def classes(inPackage: PackageName): Seq[BinaryFileEntry]
   private[dotty] def sources(inPackage: PackageName): Seq[SourceFileEntry]
 
   /**