Lint enum case in outer context

Author: som-snytt

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

@@ -189,7 +189,7 @@ class CheckUnused private (phaseMode: PhaseMode, suffix: String) extends MiniPha
     if !tree.symbol.is(Deferred) && tree.rhs.symbol != defn.Predef_undefined then
       register(tree)
     relax(tree.rhs, tree.tpt.tpe)
-    ctx
+    if tree.symbol.isAllOf(EnumCase) then ctx.outer else ctx
   override def transformValDef(tree: ValDef)(using Context): tree.type =
     traverseAnnotations(tree.symbol)
     if tree.name.startsWith("derived$") && tree.hasType then
@@ -222,6 +222,8 @@ class CheckUnused private (phaseMode: PhaseMode, suffix: String) extends MiniPha
       resolveUsage(defn.Compiletime_deferred, nme.NO_NAME, NoPrefix)
     tree
 
+  override def prepareForTypeDef(tree: TypeDef)(using Context): Context =
+    if tree.symbol.isAllOf(EnumCase) then ctx.outer else ctx
   override def transformTypeDef(tree: TypeDef)(using Context): tree.type =
     traverseAnnotations(tree.symbol)
     if !tree.symbol.is(Param) then // type parameter to do?

tests/warn/i24646.scala

@@ -0,0 +1,13 @@
+//> using options -Wunused:all
+
+import Test.OnlyFirst
+import Test.OnlyThird
+
+enum Test:
+  case First extends Test with OnlyFirst
+  case Second extends Test
+  case Third(s: String) extends Test with OnlyThird
+
+object Test:
+  sealed trait OnlyFirst
+  sealed trait OnlyThird