SI-8764 remove Xexperimental special Product members for case classes

`productElement` and `productIterator` return types under Xexperimental
use the weak lub of the case class's parameters instead of just Any.
This isn't really useful, nor tested and it is broken (SI-8764) anyway.

The special casing of `productElement` and `productIterator` was
introduced with `ProductN` support in case classes (e412524), but was
not removed when `ProductN` support went away (70996f8, d7f498a,
b7395e9, 317a105).

Author: gourlaysama

src/compiler/scala/tools/nsc/typechecker/SyntheticMethods.scala

@@ -84,24 +84,6 @@ trait SyntheticMethods extends ast.TreeDSL {
 
     def accessors = clazz.caseFieldAccessors
     val arity = accessors.size
-    // If this is ProductN[T1, T2, ...], accessorLub is the lub of T1, T2, ..., .
-    // !!! Hidden behind -Xexperimental due to bummer type inference bugs.
-    // Refining from Iterator[Any] leads to types like
-    //
-    //    Option[Int] { def productIterator: Iterator[String] }
-    //
-    // appearing legitimately, but this breaks invariant places
-    // like Tags and Arrays which are not robust and infer things
-    // which they shouldn't.
-    val accessorLub  = (
-      if (settings.Xexperimental) {
-        global.weakLub(accessors map (_.tpe.finalResultType)) match {
-          case RefinedType(parents, decls) if !decls.isEmpty => intersectionType(parents)
-          case tp                                            => tp
-        }
-      }
-      else AnyTpe
-    )
 
     def forwardToRuntime(method: Symbol): Tree =
       forwardMethod(method, getMember(ScalaRunTimeModule, (method.name prepend "_")))(mkThis :: _)
@@ -122,8 +104,8 @@ trait SyntheticMethods extends ast.TreeDSL {
       }
     }
     def productIteratorMethod = {
-      createMethod(nme.productIterator, iteratorOfType(accessorLub))(_ =>
-        gen.mkMethodCall(ScalaRunTimeModule, nme.typedProductIterator, List(accessorLub), List(mkThis))
+      createMethod(nme.productIterator, iteratorOfType(AnyTpe))(_ =>
+        gen.mkMethodCall(ScalaRunTimeModule, nme.typedProductIterator, List(AnyTpe), List(mkThis))
       )
     }
 
@@ -243,7 +225,7 @@ trait SyntheticMethods extends ast.TreeDSL {
       List(
         Product_productPrefix   -> (() => constantNullary(nme.productPrefix, clazz.name.decode)),
         Product_productArity    -> (() => constantNullary(nme.productArity, arity)),
-        Product_productElement  -> (() => perElementMethod(nme.productElement, accessorLub)(mkThisSelect)),
+        Product_productElement  -> (() => perElementMethod(nme.productElement, AnyTpe)(mkThisSelect)),
         Product_iterator        -> (() => productIteratorMethod),
         Product_canEqual        -> (() => canEqualMethod)
         // This is disabled pending a reimplementation which doesn't add any