Fix Exception in CheckUnused isOverriden() helper

compiler/src/dotty/tools/dotc/Compiler.scala

@@ -35,8 +35,7 @@ class Compiler {
   protected def frontendPhases: List[List[Phase]] =
     List(new Parser) ::             // Compiler frontend: scanner, parser
     List(new TyperPhase) ::         // Compiler frontend: namer, typer
-    List(new CheckUnused.PostTyper) ::  // Check for unused elements
-    List(new CheckShadowing) :: // Check for shadowing elements
+    List(new CheckShadowing, new CheckUnused.PostTyper) ::  // Check for unused elements // Check for shadowing elements
     List(new YCheckPositions) ::    // YCheck positions
     List(new sbt.ExtractDependencies) :: // Sends information on classes' dependencies to sbt via callbacks
     List(new semanticdb.ExtractSemanticDB) :: // Extract info into .semanticdb files

compiler/src/dotty/tools/dotc/config/ScalaSettings.scala

@@ -312,7 +312,6 @@ private sealed trait XSettings:
     helpArg = "advanced warning",
     descr = "Enable or disable specific `lint` warnings",
     choices = List(
-      ChoiceWithHelp("nowarn", ""),
       ChoiceWithHelp("all", ""),
       ChoiceWithHelp("private-shadow", "Warn if a private field or class parameter shadows a superclass field"),
       ChoiceWithHelp("type-parameter-shadow", "Warn when a type parameter shadows a type already in the scope"),
@@ -321,10 +320,8 @@ private sealed trait XSettings:
   )
 
   object XlintHas:
-    def isChoiceSet(s: String)(using Context) = Xlint.value.pipe(us => us.contains(s))
-    def allOr(s: String)(using Context) = Xlint.value.pipe(us => us.contains("all") || us.contains(s))
-    def nowarn(using Context) = allOr("nowarn")
-
+    def allOr(s: String)(using Context) =
+      Xlint.value.pipe(us => us.contains("all") || us.contains(s))
     def privateShadow(using Context) =
       allOr("private-shadow")
     def typeParameterShadow(using Context) =

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

@@ -633,6 +633,19 @@ object CheckUnused:
         imp.expr.tpe.member(sel.name.toTypeName).alternatives.exists(_.symbol.isOneOf(GivenOrImplicit))
       )
 
+    /** Returns some inherited symbol with the same type and name as the given "symDecl" */
+    private def lookForInheritedDecl(symDecl: Symbol)(using Context): Option[Symbol] =
+      val symDeclType = symDecl.info
+      val bClasses = symDecl.owner.info.baseClasses
+      bClasses match
+        case _ :: inherited =>
+          inherited
+            .map(classSymbol => symDecl.denot.matchingDecl(classSymbol, symDeclType))
+            .find(sym => sym.name == symDecl.name)
+        case Nil =>
+          None
+
+
     extension (tree: ImportSelector)
       def boundTpe: Type = tree.bound match {
         case untpd.TypedSplice(tree1) => tree1.tpe
@@ -705,8 +718,7 @@ object CheckUnused:
 
       /** A function is overriden. Either has `override flags` or parent has a matching member (type and name) */
       private def isOverriden(using Context): Boolean =
-        sym.is(Flags.Override) ||
-          (sym.exists && sym.owner.thisType.parents.exists(p => sym.matchingMember(p).exists))
+        sym.is(Flags.Override) || lookForInheritedDecl(sym).isDefined
 
     end extension
 

tests/neg-custom-args/fatal-warnings/i16639a.scala

@@ -26,11 +26,11 @@ trait Bing
 trait Accessors {
   private var v1: Int = 0 // error warn
   private var v2: Int = 0 // error warn, never set
-  private var v3: Int = 0 // warn, never got /Dotty: no warn even if not used
+  private var v3: Int = 0
   private var v4: Int = 0 // no warn
 
   private[this] var v5 = 0 // error warn, never set
-  private[this] var v6 = 0 // warn, never got /Dotty: no warn even if not used
+  private[this] var v6 = 0
   private[this] var v7 = 0 // no warn
 
   def bippy(): Int = {