Merge pull request #457 from scala/backport-lts-3.3-23325

Backport "Take inferred or explicit refinement result for unused check" to 3.3 LTS

Author: tgodzik

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

@@ -159,9 +159,7 @@ 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 _ =>
+    relax(tree.rhs, tree.tpt.tpe)
     ctx
   override def transformValDef(tree: ValDef)(using Context): tree.type =
     traverseAnnotations(tree.symbol)
@@ -183,9 +181,7 @@ class CheckUnused private (phaseMode: PhaseMode, suffix: String) extends MiniPha
       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 _ =>
+    relax(tree.rhs, tree.tpt.tpe)
     ctx
   override def transformDefDef(tree: DefDef)(using Context): tree.type =
     traverseAnnotations(tree.symbol)
@@ -902,15 +898,21 @@ object CheckUnused:
       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)
+  def relax(tree: Tree, tpe: Type)(using Context): Unit =
+    def refinements(tpe: Type, names: List[Name]): List[Name] =
+      tpe match
+      case RefinedType(parent, refinedName, refinedInfo) => refinedName :: refinements(parent, names)
+      case _ => names
+    val refinedNames = refinements(tpe, Nil)
+    if !refinedNames.isEmpty then
+      val names = refinedNames.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)

tests/warn/i22681.scala

@@ -6,12 +6,10 @@ trait T:
 
 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
+    def g = 42 // warn effectively private member is unused
+    def t = 42 // nowarn
+    def u = 42 // 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
+    def u = 42 // nowarn because leaked by refinement

tests/warn/i23323.scala

@@ -0,0 +1,14 @@
+//> using options -Wunused:all
+
+class C:
+  val x = new reflect.Selectable:
+    def f = 42
+    def g = 27
+  val y: Selectable = new reflect.Selectable:
+    def f = 42 // warn
+    def g = 27 // warn
+  val z = new scala.Selectable:
+    def f = 42
+    def g = 27
+    def selectDynamic(name: String): Any = ???
+    def applyDynamic(name: String)(args: Any*): Any = ???