Fix #2072: erasure and refchecks

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

@@ -594,14 +594,19 @@ object Erasure extends TypeTestsCasts{
 
     override def typedStats(stats: List[untpd.Tree], exprOwner: Symbol)(implicit ctx: Context): List[Tree] = {
       val stats1 = Trees.flatten(super.typedStats(stats, exprOwner))
-      if (ctx.owner.isClass) stats1 ::: addBridges(stats, stats1)(ctx) else stats1
+      if (ctx.owner.isClass) {
+        val newBridges = addBridges(stats, stats1)(ctx)
+        val keptStats = stats1.filter(x => !newBridges.exists(_.symbol == x.symbol))
+        keptStats ::: newBridges.filter(!_.isEmpty)
+      }
+      else stats1
     }
 
     // this implementation doesn't check for bridge clashes with value types!
     def addBridges(oldStats: List[untpd.Tree], newStats: List[tpd.Tree])(implicit ctx: Context): List[tpd.Tree] = {
       val beforeCtx = ctx.withPhase(ctx.erasurePhase)
       def traverse(after: List[Tree], before: List[untpd.Tree],
-                   emittedBridges: ListBuffer[tpd.DefDef] = ListBuffer[tpd.DefDef]()): List[tpd.DefDef] = {
+                   emittedBridges: ListBuffer[tpd.Tree] = ListBuffer[tpd.Tree]()): List[tpd.Tree] = {
         after match {
           case Nil => emittedBridges.toList
           case (member: DefDef) :: newTail =>
@@ -629,7 +634,7 @@ object Erasure extends TypeTestsCasts{
                         sym =>
                           (sym.name eq bridge.name) && sym.info.widen =:= bridge.info.widen
                       }.orElse(
-                        emittedBridges.find(stat => (stat.name == bridge.name) && stat.tpe.widen =:= bridge.info.widen)
+                        emittedBridges.find(stat => stat.isDef && (stat.asInstanceOf[DefDef].name == bridge.name) && stat.tpe.widen =:= bridge.info.widen)
                           .map(_.symbol))
                       clash match {
                         case Some(cl) =>
@@ -642,7 +647,22 @@ object Erasure extends TypeTestsCasts{
                   }
 
                   val bridgeImplementations = minimalSet.map {
-                    sym => makeBridgeDef(member, sym)(ctx)
+                    sym =>
+                      if (member.symbol.is(Flags.Deferred)) {
+                        if (!sym.is(Flags.Deferred)) {
+                          // sometimes we need to forward an abstract method in a subclass to a non-abstract method in parent.
+                          // see https://github.com/lampepfl/dotty/issues/2072 for illustrations
+
+                          val d = member.symbol.copySymDenotation(initFlags = member.symbol.flags.&~(Flags.Deferred))
+                          d.installAfter(ctx.erasurePhase.asInstanceOf[Erasure])
+                          // Dark magic. Don't look here. 
+                          d.transformAfter(ctx.erasurePhase.asInstanceOf[Erasure],
+                            x => if (x.is(Flags.Deferred)) x.copySymDenotation(initFlags = x.flags.&~(Flags.Deferred)) else x
+                          )
+                          makeBridgeDef(newSymbol.owner, sym, newSymbol)(ctx)
+                        }
+                        else EmptyTree
+                      } else makeBridgeDef(newSymbol.owner, newSymbol, sym)(ctx)
                   }
                   emittedBridges ++= bridgeImplementations
                 } catch {
@@ -665,28 +685,34 @@ object Erasure extends TypeTestsCasts{
 
     /** Create a bridge DefDef which overrides a parent method.
      *
-     *  @param newDef     The DefDef which needs bridging because its signature
+     *  @param newDefSym     The DefDef which needs bridging because its signature
      *                    does not match the parent method signature
      *  @param parentSym  A symbol corresponding to the parent method to override
      *  @return           A new DefDef whose signature matches the parent method
      *                    and whose body only contains a call to newDef
      */
-    def makeBridgeDef(newDef: tpd.DefDef, parentSym: Symbol)(implicit ctx: Context): tpd.DefDef = {
-      val newDefSym = newDef.symbol
-      val currentClass = newDefSym.owner.asClass
+    def makeBridgeDef(currentClass: Symbol, newDefSym: Symbol, parentSym: Symbol)(implicit ctx: Context): tpd.DefDef = {
 
       def error(reason: String) = {
         assert(false, s"failure creating bridge from ${newDefSym} to ${parentSym}, reason: $reason")
         ???
       }
       var excluded = NoBridgeFlags
       if (!newDefSym.is(Flags.Protected)) excluded |= Flags.Protected // needed to avoid "weaker access" assertion failures in expandPrivate
-      val bridge = ctx.newSymbol(currentClass,
-        parentSym.name, parentSym.flags &~ excluded | Flags.Bridge, parentSym.info, coord = newDefSym.owner.coord).asTerm
-      bridge.enteredAfter(ctx.phase.prev.asInstanceOf[DenotTransformer]) // this should be safe, as we're executing in context of next phase
+      val bridge =
+        if (newDefSym.owner == currentClass) {
+          // we are forwarding a method in a superclass to a implementation in a subclass
+          val s = ctx.newSymbol(currentClass,
+            parentSym.name, parentSym.flags &~ excluded | Flags.Bridge, parentSym.info, coord = newDefSym.owner.coord).asTerm
+          s.enteredAfter(ctx.phase.prev.asInstanceOf[DenotTransformer]) // this should be safe, as we're executing in context of next phase
+          s
+        } else {
+          // we are forwarding a method defined in a subclass to an implementation in a superclass
+          parentSym.asTerm
+        }
       ctx.debuglog(s"generating bridge from ${newDefSym} to $bridge")
 
-      val sel: Tree = This(currentClass).select(newDefSym.termRef)
+      val sel: Tree = This(currentClass.asClass).select(newDefSym.termRef)
 
       val resultType = parentSym.info.widen.resultType
 

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

@@ -96,23 +96,30 @@ trait TypeTestsCasts {
         /** Transform isInstanceOf OrType
          *
          *    expr.isInstanceOf[A | B]  ~~>  expr.isInstanceOf[A] | expr.isInstanceOf[B]
+         *    expr.isInstanceOf[A & B]  ~~>  expr.isInstanceOf[A] & expr.isInstanceOf[B]
          *
          *  The transform happens before erasure of `argType`, thus cannot be merged
          *  with `transformIsInstanceOf`, which depends on erased type of `argType`.
          */
-        def transformOrTypeTest(qual: Tree, argType: Type): Tree = argType.dealias match {
+        def transformTypeTest(qual: Tree, argType: Type): Tree = argType.dealias match {
           case OrType(tp1, tp2) =>
             evalOnce(qual) { fun =>
-              transformOrTypeTest(fun, tp1)
-                .select(nme.OR)
-                .appliedTo(transformOrTypeTest(fun, tp2))
+              transformTypeTest(fun, tp1)
+                .select(defn.Boolean_||)
+                .appliedTo(transformTypeTest(fun, tp2))
+            }
+          case AndType(tp1, tp2) =>
+            evalOnce(qual) { fun =>
+              transformTypeTest(fun, tp1)
+                .select(defn.Boolean_&&)
+                .appliedTo(transformTypeTest(fun, tp2))
             }
           case _ =>
             transformIsInstanceOf(qual, erasure(argType))
         }
 
         if (sym eq defn.Any_isInstanceOf)
-          transformOrTypeTest(qual, tree.args.head.tpe)
+          transformTypeTest(qual, tree.args.head.tpe)
         else if (sym eq defn.Any_asInstanceOf)
           transformAsInstanceOf(erasure(tree.args.head.tpe))
         else tree

compiler/src/dotty/tools/dotc/typer/RefChecks.scala

@@ -406,7 +406,8 @@ object RefChecks {
       def ignoreDeferred(member: SingleDenotation) =
         member.isType ||
           member.symbol.is(SuperAccessor) || // not yet synthesized
-          member.symbol.is(JavaDefined) && hasJavaErasedOverriding(member.symbol)
+          member.symbol.is(JavaDefined) && hasJavaErasedOverriding(member.symbol) ||
+          member.symbol.allOverriddenSymbols.exists(!_.is(Flags.Deferred)) // has an implementation in super
 
       // 2. Check that only abstract classes have deferred members
       def checkNoAbstractMembers(): Unit = {

tests/pos/i2073.scala

@@ -0,0 +1,2 @@
+final case class Fix[F[_]](unfix: F[Fix[F]]) extends AnyVal
+

tests/run/i2072.scala

@@ -0,0 +1,28 @@
+trait T { 
+  def m = "" ; 
+  val v = "" ; 
+  lazy val lv = ""; 
+  object o
+}
+
+// deferred methods always lose against concrete ones, so none of these declarations actually survive in bytecode
+// the mixed in members from T take precedence in the linearisation order
+abstract class AC extends T {
+  def m: Any
+  def v: Any
+  def lv: Any
+  def o: Any
+}
+
+class C extends AC{}
+
+object Test {
+ def main(args: Array[String]): Unit = {
+   val c = new C
+   c.m
+   c.v
+   c.lv
+   c.o
+ }
+} 
+

tests/run/i2072b.scala

@@ -0,0 +1,28 @@
+trait T { 
+  def m = "" ; 
+  val v = "" ; 
+  lazy val lv = "";
+  object o;
+}
+
+// deferred methods always lose against concrete ones, so none of these declarations actually survive in bytecode
+// the mixed in members from T take precedence in the linearisation order
+abstract class AC{
+  def m: Any
+  def v: Any
+  def lv: Any
+  def o: Any
+}
+
+class C extends AC with T{}
+
+object Test {
+ def main(args: Array[String]): Unit = {
+   val c = new C
+   c.m
+   c.v
+   c.lv
+   c.o
+ }
+} 
+

tests/run/i2072c.scala

@@ -0,0 +1,41 @@
+trait T { lazy val x: String = "foo" }
+trait U { def x: Any }
+class AC extends T with U // { def x: Any }
+
+abstract class B { def x: Any }
+class C extends B { def x: String = "abc" }
+
+package p2 {
+trait T1 { def f: Any }
+trait T2 extends T1 { def f: Number = ??? }
+trait T3 extends T1 { override def f: Integer = ??? }
+class C extends T2 with T3
+}
+
+package p3 {
+
+  trait A { def f: Any }
+  trait B extends A { def f: String }
+  class C extends B { def f = "abc" }
+
+}
+
+object Test {
+  def main(args: Array[String]): Unit = {
+     val ac = new AC
+     ac.x
+     (ac: T).x
+     (ac: U).x
+     (new C).x
+     ((new C): B).x
+     val p2c = new p2.C
+     p2c.f
+     (p2c: p2.T1).f
+     (p2c: p2.T2).f
+     (p2c: p2.T3).f
+     val p3c = new p3.C
+     p3c.f
+     (p3c: p3.A).f
+     (p3c: p3.B).f
+  }
+}