Warn for top level private

Author: som-snytt

compiler/src/dotty/tools/dotc/transform/CheckUnused.scala

@@ -697,10 +697,12 @@ object CheckUnused:
         !sym.shouldNotReportParamOwner
 
       private def shouldReportPrivateDef(using Context): Boolean =
+        val sym = memDef.symbol
         peekScopeType == ScopeType.Template
-        && !memDef.symbol.isConstructor
-        && memDef.symbol.is(Private, butNot = SelfName | Synthetic | CaseAccessor)
-        && !ignoredSignature(memDef.symbol)
+        && !sym.isConstructor
+        && (sym.is(Private, butNot = SelfName | Synthetic | CaseAccessor)
+         || sym.effectiveOwner.is(PackageClass) && sym.denot.privateWithin == sym.effectiveOwner)
+        && !ignoredSignature(sym)
 
       private def isUnsetVarDef(using Context): Boolean =
         val sym = memDef.symbol

tests/warn/unused-privates.scala

@@ -285,3 +285,13 @@ class `absolve ONLY serial framework`:
   private def readObjectNoData(): Unit = () // warn
   @throws(classOf[ObjectStreamException])
   private def readResolve(): Object = ??? // warn
+
+@throws(classOf[java.io.ObjectStreamException])
+private def readResolve(): Object = ??? // warn
+private def print() = println() // warn
+private val printed = false // warn
+
+package locked:
+  private[locked] def locker(): Unit = () // warn as we cannot distinguish unqualified private at top level
+  package basement:
+    private[locked] def shackle(): Unit = () // no warn as it is not top level at boundary