Clarify conflict logic bypass for PolyFunctions.

Author: milessabin

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

@@ -83,14 +83,19 @@ class ElimErasedValueType extends MiniPhase with InfoTransformer { thisPhase =>
       override def matches(sym1: Symbol, sym2: Symbol) =
         sym1.signature == sym2.signature
     }
+
     def checkNoConflict(sym1: Symbol, sym2: Symbol, info: Type)(implicit ctx: Context): Unit = {
       val site = root.thisType
       val info1 = site.memberInfo(sym1)
       val info2 = site.memberInfo(sym2)
-      if (!info1.matchesLoosely(info2) &&
-          !(sym1.name == nme.apply &&
-            (sym1.owner.derivesFrom(defn.PolyFunctionClass) ||
-             sym2.owner.derivesFrom(defn.PolyFunctionClass))))
+      // PolyFunction apply methods will be eliminated later during
+      // ElimPolyFunction, so we let them pass here.
+      def bothPolyApply =
+        sym1.name == nme.apply &&
+        (sym1.owner.derivesFrom(defn.PolyFunctionClass) ||
+         sym2.owner.derivesFrom(defn.PolyFunctionClass))
+
+      if (!info1.matchesLoosely(info2) && !bothPolyApply)
         ctx.error(DoubleDefinition(sym1, sym2, root), root.sourcePos)
     }
     val earlyCtx = ctx.withPhase(ctx.elimRepeatedPhase.next)