Warn unused member of anonymous class

Author: som-snytt

Diff for: compiler/src/dotty/tools/dotc/transform/CheckUnused.scala

@@ -517,7 +517,7 @@ 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
@@ -758,7 +758,7 @@ 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)
@@ -879,6 +879,9 @@ 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

Diff for: tests/semanticdb/metac.expect

@@ -3494,7 +3494,7 @@ Text => empty
 Language => Scala
 Symbols => 12 entries
 Occurrences => 33 entries
-Diagnostics => 1 entries
+Diagnostics => 2 entries
 Synthetics => 4 entries
 
 Symbols:
@@ -3550,6 +3550,7 @@ Diagnostics:
 [14:20..14:23): [warning] Alphanumeric method foo is not declared infix; it should not be used as infix operator.
 Instead, use method syntax .foo(...) or backticked identifier `foo`.
 The latter can be rewritten automatically under -rewrite -source 3.4-migration.
+[19:8..19:17): [warning] unused private member
 
 Synthetics:
 [12:2..12:6):user => reflectiveSelectable(*)

Diff for: tests/warn/i22681.scala

@@ -0,0 +1,13 @@
+
+//> 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 // warn despite structural type