ProductN, and method synthesis toolbox.

- Finished giving case classes a ProductN parent, and flipped it on. The
"finish" part involved not breaking existing code where case classes
manually extend the appropriate ProductN. (Like, Tuple 1-22.)

- Generalized most of SyntheticMethods to ease method creation and class
manipulation in general.

- Fixed bugs related to the above, like the fact that this used to be a
compile error:

  scala> case class Foo() extends Serializable
  <console>:28: error: trait Serializable is inherited twice
         case class Foo() extends Serializable
                                  ^
It feels like there's a better way to eliminate the duplicate parents,
but after spending a lot of time chasing my tail in that peril-fraught
zone between namer and typer, I don't see an easy path to improve on
it.  Closes SI-1799.  For that modification to Typers, review by odersky.

1 files changed, 5 insertions, 5 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Unapplies.scala b/src/compiler/scala/tools/nsc/typechecker/Unapplies.scala
index 67dd272d5a..4f7e6225e1 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Unapplies.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Unapplies.scala
@@ -42,11 +42,11 @@ trait Unapplies extends ast.TreeDSL
     tp.typeSymbol match {                             // unapplySeqResultToMethodSig
       case BooleanClass             => Nil
       case OptionClass | SomeClass  =>
-        val prod = tp.typeArgs.head
-        getProductArgs(prod) match {
-          case Some(xs) if xs.size > 1  => xs         // n > 1
-          case _                        => List(prod) // special n == 0 ||  n == 1
-        }
+        val prod  = tp.typeArgs.head
+        val targs = getProductArgs(prod)
+
+        if (targs.isEmpty || targs.tail.isEmpty) List(prod) // special n == 0 ||  n == 1
+        else targs  // n > 1
       case _                        =>
         throw new TypeError("result type "+tp+" of unapply not in {Boolean, Option[_], Some[_]}")
     }