Check Override before looking for overridden

[Cherry-picked 8253ee2]

Author: som-snytt

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

@@ -923,7 +923,7 @@ object CheckUnused:
       }
     def isEffectivelyPrivate: Boolean =
       sym.is(Private, butNot = ParamAccessor)
-      || sym.owner.isAnonymousClass && !sym.nextOverriddenSymbol.exists
+      || sym.owner.isAnonymousClass && !sym.is(Override) && !sym.nextOverriddenSymbol.exists
     // pick the symbol the user wrote for purposes of tracking
     inline def userSymbol: Symbol=
       if sym.denot.is(ModuleClass) then sym.denot.companionModule else sym

tests/warn/i22896/J.java

@@ -0,0 +1,6 @@
+
+public class J {
+    private int i = 42;
+    public int i() { return 27; }
+    public String i(int j) { return "hello, world"; }
+}

tests/warn/i22896/s.scala

@@ -0,0 +1,13 @@
+//> using options -Werror -Wunused:privates
+
+def f =
+  new J:
+    override val i = -1 // nowarn, trust override
+
+def g =
+  new J:
+    override def i = -1 // nowarn, trust override
+
+def h =
+  new J:
+    override def i() = -1 // nowarn correctly matches signature