Consult self type for overrides

Author: som-snytt

compiler/src/dotty/tools/dotc/core/SymDenotations.scala

@@ -1953,7 +1953,7 @@ object SymDenotations {
       case _ => NoSymbol
 
     /** The explicitly given self type (self types of modules are assumed to be
-     *  explcitly given here).
+     *  explicitly given here).
      */
     def givenSelfType(using Context): Type = classInfo.selfInfo match {
       case tp: Type => tp

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

@@ -926,7 +926,13 @@ object CheckUnused:
       sym.is(Private, butNot = ParamAccessor)
       || sym.owner.isAnonymousClass && !sym.isEffectivelyOverride
     def isEffectivelyOverride: Boolean =
-      sym.is(Override) || sym.allOverriddenSymbols.hasNext
+      sym.is(Override)
+      ||
+      sym.canMatchInheritedSymbols && { // inline allOverriddenSymbols using owner.info or thisType
+        val owner = sym.owner.asClass
+        val base = if owner.classInfo.selfInfo != NoType then owner.thisType else owner.info
+        base.baseClasses.drop(1).iterator.exists(sym.overriddenSymbol(_).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/unused-params.scala

@@ -122,7 +122,7 @@ trait BadMix { self: InterFace =>
     a
   }
   override def call(a: Int,
-                    XXXX: String,               // warn no longer excused because required by superclass
+                    XXXX: String, // no warn still excused because override (required by self type)
                     c: Double): Int = {
     println(c)
     a
@@ -135,6 +135,14 @@ trait BadMix { self: InterFace =>
   def i(implicit s: String) = answer           // warn
 }
 
+trait ImplFace:
+  self: InterFace =>
+  def call(a: Int,
+           b: String, // no warn required by self type
+           c: Double): Int =
+    println(c)
+    a
+
 class Unequal {
   override def equals(other: Any) = toString.nonEmpty   // no warn (override)
 }