Warn unused member of anonymous class

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

@@ -150,6 +150,9 @@ class CheckUnused private (phaseMode: PhaseMode, suffix: String) extends MiniPha
   override def prepareForValDef(tree: ValDef)(using Context): Context =
     if !tree.symbol.is(Deferred) && tree.rhs.symbol != defn.Predef_undefined then
       refInfos.register(tree)
+    tree.tpt match
+    case RefinedTypeTree(_, refinements) => relax(tree.rhs, refinements)
+    case _ =>
     ctx
   override def transformValDef(tree: ValDef)(using Context): tree.type =
     traverseAnnotations(tree.symbol)
@@ -170,11 +173,15 @@ class CheckUnused private (phaseMode: PhaseMode, suffix: String) extends MiniPha
   override def prepareForDefDef(tree: DefDef)(using Context): Context =
     def trivial = tree.symbol.is(Deferred) || isUnconsuming(tree.rhs)
     def nontrivial = tree.symbol.isConstructor || tree.symbol.isAnonymousFunction
-    if !nontrivial && trivial then refInfos.skip.addOne(tree.symbol)
+    if !nontrivial && trivial then
+      refInfos.skip.addOne(tree.symbol)
     if tree.symbol.is(Inline) then
       refInfos.inliners += 1
     else if !tree.symbol.is(Deferred) && tree.rhs.symbol != defn.Predef_undefined then
       refInfos.register(tree)
+    tree.tpt match
+    case RefinedTypeTree(_, refinements) => relax(tree.rhs, refinements)
+    case _ =>
     ctx
   override def transformDefDef(tree: DefDef)(using Context): tree.type =
     traverseAnnotations(tree.symbol)
@@ -456,7 +463,7 @@ object CheckUnused:
         if !tree.name.isInstanceOf[DerivedName] then
           pats.addOne((tree.symbol, tree.namePos))
       case tree: NamedDefTree =>
-        if (tree.symbol ne NoSymbol) && !tree.name.isWildcard then
+        if (tree.symbol ne NoSymbol) && !tree.name.isWildcard && !tree.hasAttachment(NoWarn) then
           defs.addOne((tree.symbol, tree.namePos))
       case _ =>
         if tree.symbol ne NoSymbol then
@@ -520,7 +527,7 @@ object CheckUnused:
     def checkPrivate(sym: Symbol, pos: SrcPos) =
       if ctx.settings.WunusedHas.privates
         && !sym.isPrimaryConstructor
-        && sym.is(Private, butNot = SelfName | Synthetic | CaseAccessor)
+        && !sym.isOneOf(SelfName | Synthetic | CaseAccessor)
         && !sym.name.is(BodyRetainerName)
         && !sym.isSerializationSupport
         && !(sym.is(Mutable) && sym.isSetter && sym.owner.is(Trait)) // tracks sym.underlyingSymbol sibling getter
@@ -764,7 +771,7 @@ object CheckUnused:
     for (sym, pos) <- infos.defs.iterator if !sym.hasAnnotation(defn.UnusedAnnot) do
       if infos.refs(sym) then
         checkUnassigned(sym, pos)
-      else if sym.is(Private, butNot = ParamAccessor) then
+      else if sym.isEffectivelyPrivate then
         checkPrivate(sym, pos)
       else if sym.is(Param, butNot = Given | Implicit) then
         checkParam(sym, pos)
@@ -851,6 +858,17 @@ object CheckUnused:
         args.foreach(traverse)
       case tree => traverseChildren(tree)
 
+  // NoWarn members in tree that correspond to refinements; currently uses only names.
+  def relax(tree: Tree, refinements: List[Tree])(using Context): Unit =
+    val names = refinements.collect { case named: NamedDefTree => named.name }.toSet
+    val relaxer = new TreeTraverser:
+      def traverse(tree: Tree)(using Context) =
+        tree match
+        case tree: NamedDefTree if names(tree.name) => tree.withAttachment(NoWarn, ())
+        case _ =>
+        traverseChildren(tree)
+    relaxer.traverse(tree)
+
   extension (nm: Name)
     inline def exists(p: Name => Boolean): Boolean = nm.ne(nme.NO_NAME) && p(nm)
     inline def isWildcard: Boolean = nm == nme.WILDCARD || nm.is(WildcardParamName)
@@ -885,6 +903,9 @@ object CheckUnused:
       sym.isClass && sym.info.allMembers.forall: d =>
         val m = d.symbol
         !m.isTerm || m.isSelfSym || m.is(Method) && (m.owner == defn.AnyClass || m.owner == defn.ObjectClass)
+    def isEffectivelyPrivate(using Context): Boolean =
+      sym.is(Private, butNot = ParamAccessor)
+      || sym.owner.isAnonymousClass && !sym.nextOverriddenSymbol.exists
 
   extension (sel: ImportSelector)
     def boundTpe: Type = sel.bound match

tests/warn/i22681.scala

@@ -0,0 +1,17 @@
+
+//> using options -Wunused:all
+
+trait T:
+  def t: Int
+
+class C:
+  def f: Runnable { def u: Int } = new Runnable with T:
+    private def v = 42 // avoid g judged too trivial to warn
+    def run() = ()
+    def g = v // warn effectively private member is unused
+    def t = v // nowarn
+    def u = v // nowarn because leaked by refinement
+  val v: Runnable { def u: Int } = new Runnable:
+    private def v = 42 // avoid g judged too trivial to warn
+    def run() = ()
+    def u = v // nowarn because leaked by refinement