Don't use empty files to indicate presence of tasty in class path.

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

@@ -205,16 +205,16 @@ class GenBCodePipeline(val entryPoints: List[Symbol], val int: DottyBackendInter
             val dataAttr = new CustomAttr(nme.TASTYATTR.mangledString, binary)
             val store = if (mirrorC ne null) mirrorC else plainC
             store.visitAttribute(dataAttr)
-            val outTastyFile = getFileForClassfile(outF, store.name, ".tasty")
             if (ctx.settings.emitTasty.value) {
+              val outTastyFile = getFileForClassfile(outF, store.name, ".tasty")
               val outstream = new DataOutputStream(outTastyFile.bufferedOutput)
 
               try outstream.write(binary)
               finally outstream.close()
-            } else if (!outTastyFile.isVirtual) {
+            } 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
-              outTastyFile.create()
+              getFileForClassfile(outF, store.name, ".hasTasty")
             }
           }
 

compiler/src/dotty/tools/dotc/interactive/InteractiveDriver.scala

@@ -85,12 +85,13 @@ class InteractiveDriver(settings: List[String]) extends Driver {
               binFile.name.stripSuffix(".class")
             else
               null
+          // Presence of a file with one of these suffixes indicates that the
+          // corresponding class has been pickled with TASTY.
+          val tastySuffixes = List(".hasTasty", ".tasty")
           prefix != null && {
-            val tastyFile = prefix + ".tasty"
             binFile match {
               case pf: PlainFile =>
-                val tastyPath = pf.givenPath.parent / tastyFile
-                tastyPath.exists
+                tastySuffixes.map(suffix => pf.givenPath.parent / (prefix + suffix)).exists(_.exists)
               case _ =>
                 sys.error(s"Unhandled file type: $binFile [getClass = ${binFile.getClass}]")
             }

project/Build.scala

@@ -880,7 +880,7 @@ object Build {
 
 
       sbtPlugin := true,
-      version := "0.1.0",
+      version := "0.1.1",
       ScriptedPlugin.scriptedSettings,
       ScriptedPlugin.sbtTestDirectory := baseDirectory.value / "sbt-test",
       ScriptedPlugin.scriptedBufferLog := false,

sbt-dotty/src/dotty/tools/sbtplugin/DottyPlugin.scala

@@ -79,27 +79,27 @@ object DottyPlugin extends AutoPlugin {
     }
   }
 
-  /** Patches the IncOptions so that .tasty files are pruned as needed.
+  /** Patches the IncOptions so that .tasty and .hasTasty files are pruned as needed.
    *
    *  This code is adapted from `scalaJSPatchIncOptions` in Scala.js, which needs
    *  to do the exact same thing but for classfiles.
    *
    *  This complicated logic patches the ClassfileManager factory of the given
-   *  IncOptions with one that is aware of .tasty files emitted by the Dotty
+   *  IncOptions with one that is aware of .tasty and .hasTasty files emitted by the Dotty
    *  compiler. This makes sure that, when a .class file must be deleted, the
-   *  corresponding .tasty file is also deleted.
+   *  corresponding .tasty or .hasTasty file is also deleted.
    */
   def dottyPatchIncOptions(incOptions: IncOptions): IncOptions = {
     val inheritedNewClassfileManager = incOptions.newClassfileManager
     val newClassfileManager = () => new ClassfileManager {
       private[this] val inherited = inheritedNewClassfileManager()
 
       def delete(classes: Iterable[File]): Unit = {
+        val tastySuffixes = List(".tasty", ".hasTasty")
         inherited.delete(classes flatMap { classFile =>
           val dottyFiles = if (classFile.getPath endsWith ".class") {
-            val f = new File(classFile.getAbsolutePath.stripSuffix(".class") + ".tasty")
-            if (f.exists) List(f)
-            else Nil
+            val prefix = classFile.getAbsolutePath.stripSuffix(".class")
+            tastySuffixes.map(suffix => new File(prefix + suffix)).filter(_.exists)
           } else Nil
           classFile :: dottyFiles
         })