Fix extending protected nested java classes

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

@@ -103,13 +103,14 @@ object SymbolLoaders {
    */
   def enterClassAndModule(
       owner: Symbol, name: PreName, completer: SymbolLoader,
-      flags: FlagSet = EmptyFlags, scope: Scope = EmptyScope)(using Context): Unit = {
+      flags: FlagSet = EmptyFlags, scope: Scope = EmptyScope)(using Context): (Symbol, Symbol) = {
     val clazz = enterClass(owner, name, completer, flags, scope)
     val module = enterModule(
       owner, name, completer,
       modFlags = flags.toTermFlags & RetainedModuleValFlags,
       clsFlags = flags.toTypeFlags & RetainedModuleClassFlags,
       scope = scope)
+    (clazz, module)
   }
 
   /** Enter all toplevel classes and objects in file `src` into package `owner`, provided

compiler/src/dotty/tools/dotc/core/classfile/ClassfileParser.scala

@@ -403,9 +403,10 @@ class ClassfileParser(
 
       val privateWithin = getPrivateWithin(jflags)
 
-      classRoot.setPrivateWithin(privateWithin)
-      moduleRoot.setPrivateWithin(privateWithin)
-      moduleRoot.sourceModule.setPrivateWithin(privateWithin)
+      if privateWithin.exists then
+        classRoot.setPrivateWithin(privateWithin)
+        moduleRoot.setPrivateWithin(privateWithin)
+        moduleRoot.sourceModule.setPrivateWithin(privateWithin)
 
       for (i <- 0 until in.nextChar) parseMember(method = false)
       for (i <- 0 until in.nextChar) parseMember(method = true)
@@ -1058,13 +1059,18 @@ class ClassfileParser(
    */
   private def enterOwnInnerClasses()(using Context, DataReader): Unit = {
     def enterClassAndModule(entry: InnerClassEntry, file: AbstractFile, jflags: Int) =
-      SymbolLoaders.enterClassAndModule(
+      val (cls, mod) = SymbolLoaders.enterClassAndModule(
           getOwner(jflags),
-          entry.originalName,
+        entry.originalName,
           new ClassfileLoader(file),
           classTranslation.flags(jflags),
           getScope(jflags))
 
+      val privateWithin = getPrivateWithin(jflags)
+      cls.setPrivateWithin(privateWithin)
+      mod.setPrivateWithin(privateWithin)
+      mod.sourceModule.setPrivateWithin(privateWithin)
+
     for entry <- innerClasses.valuesIterator do
       // create a new class member for immediate inner classes
       if entry.outer.name == currentClassName then

compiler/src/dotty/tools/dotc/printing/Formatting.scala

@@ -109,6 +109,13 @@ object Formatting {
           case Atoms.Range(lo, hi) => CtxShow(s"Range(${toStr(lo.toList)}, ${toStr(hi.toList)})")
       end given
 
+      given Show[ast.untpd.Modifiers] with
+        def show(x: ast.untpd.Modifiers) =
+          CtxShow(s"Modifiers(${toStr(x.flags)}, ${toStr(x.privateWithin)}, ${toStr(x.annotations)}, ${toStr(x.mods)})")
+
+      given Show[ast.untpd.Mod] with
+        def show(x: ast.untpd.Mod) = CtxShow(s"Mod(${toStr(x.flags)})")
+
       given Show[Showable]                            = ShowAny
       given Show[Shown]                               = ShowAny
       given Show[Int]                                 = ShowAny

tests/pos/i21631_joint/AbstractChannel.java

@@ -0,0 +1,7 @@
+public abstract class AbstractChannel {
+    protected AbstractChannel() {}
+    protected abstract AbstractUnsafe newUnsafe();
+    protected abstract class AbstractUnsafe {
+        public abstract void connect();
+    }
+}

tests/pos/i21631_joint/i21631.scala

@@ -0,0 +1,5 @@
+class Channel extends AbstractChannel() {
+  override def newUnsafe(): AbstractChannel#AbstractUnsafe = new AbstractUnsafe {
+    override def connect(): Unit = ???
+  }
+}

tests/pos/i21631_separ/AbstractChannel_1.java

@@ -0,0 +1,7 @@
+public abstract class AbstractChannel_1 {
+    protected AbstractChannel_1() {}
+    protected abstract AbstractUnsafe newUnsafe();
+    protected abstract class AbstractUnsafe {
+        public abstract void connect();
+    }
+}

tests/pos/i21631_separ/i21631_2.scala

@@ -0,0 +1,5 @@
+class Channel extends AbstractChannel_1() {
+  override def newUnsafe(): AbstractChannel_1#AbstractUnsafe = new AbstractUnsafe {
+    override def connect(): Unit = ???
+  }
+}