Allow overriding artifacts when generating bridges

Author: anatoliykmetyuk

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

@@ -1141,7 +1141,7 @@ object SymDenotations {
      *  either as overrider or overridee.
      */
     final def memberCanMatchInheritedSymbols(implicit ctx: Context): Boolean =
-      !isConstructor && !is(Private | Artifact)
+      !isConstructor && !is(Private)
 
     /** The symbol, in class `inClass`, that is overridden by this denotation in class `siteClass`.*/
     final def overriddenSymbol(inClass: ClassSymbol, siteClass: ClassSymbol = owner.asClass)(implicit ctx: Context): Symbol =

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

@@ -19,7 +19,7 @@ class Bridges(root: ClassSymbol, thisPhase: DenotTransformer)(implicit ctx: Cont
   private val preErasureCtx = ctx.withPhase(ctx.erasurePhase)
   private val elimErasedCtx = ctx.withPhase(ctx.elimErasedValueTypePhase.next)
 
-  private class BridgesCursor(implicit ctx: Context) extends OverridingPairs.Cursor(root) {
+  private class BridgesCursor(implicit ctx: Context) extends OverridingPairs.Cursor(root, excludeArtifacts = false) {
 
     /** Only use the superclass of `root` as a parent class. This means
      *  overriding pairs that have a common implementation in a trait parent

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

@@ -20,14 +20,15 @@ object OverridingPairs {
   /** The cursor class
    *  @param base   the base class that contains the overriding pairs
    */
-  class Cursor(base: Symbol)(implicit ctx: Context) {
+  class Cursor(base: Symbol, excludeArtifacts: Boolean = true)(implicit ctx: Context) {
 
     private val self = base.thisType
 
     /** Symbols to exclude: Here these are constructors and private locals.
      *  But it may be refined in subclasses.
      */
-    protected def exclude(sym: Symbol): Boolean = !sym.memberCanMatchInheritedSymbols
+    protected def exclude(sym: Symbol): Boolean =
+      !sym.memberCanMatchInheritedSymbols || (excludeArtifacts && sym.is(Artifact))
 
     /** The parents of base that are checked when deciding whether an overriding
      *  pair has already been treated in a parent class.