Get tastyInfo from topLevelClass

Author: EugeneFlesselle

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

@@ -119,12 +119,8 @@ class SymUtils:
     /** Is a case class for which mirrors support access to default arguments.
      */
     def mirrorSupportsDefaultArguments(using Context): Boolean =
-      !self.is(JavaDefined) && !self.is(Scala2x) && self.isClass && {
-        val compUnitInfo = self.asClass.compUnitInfo
-        compUnitInfo != null && (compUnitInfo.nn.tastyInfo match
-          case None => true // was not loaded from TASTy
-          case Some(TastyInfo(TastyVersion(major, minor, exp), _)) => major == 28 && minor >= 4)
-      }
+      !self.is(JavaDefined) && !self.is(Scala2x) && self.isClass && self.tastyInfo.forall:
+        case TastyInfo(TastyVersion(major, minor, exp), _) => major == 28 && minor >= 4
 
     /** Is this an old style implicit conversion?
      *  @param directOnly            only consider explicitly written methods