Use source file from TASTy attribute when available

Author: nicolasstucki

compiler/src/dotty/tools/dotc/core/Symbols.scala

@@ -486,6 +486,12 @@ object Symbols extends SymUtils {
           mySource = ctx.getSource(file)
         else
           mySource = defn.patchSource(this)
+          if !mySource.exists then
+            val compUnitInfo = compilationUnitInfo
+            if compUnitInfo != null then
+              compUnitInfo.tastyInfo.flatMap(_.attributes.sourceFile) match
+                case Some(path) => mySource = ctx.getSource(path)
+                case _ =>
           if !mySource.exists then
             mySource = atPhaseNoLater(flattenPhase) {
               denot.topLevelClass.unforcedAnnotation(defn.SourceFileAnnot) match