wip: sling @uncheckedVariance around some more

Author: SethTisue

core/src/main/scala/scala/collection/generic/GenericTraversableTemplate.scala

@@ -63,7 +63,7 @@ trait GenericTraversableTemplate[+A, +CC[X] <: ParIterable[X]] extends HasNewBui
 
   /** The builder that builds instances of type $Coll[A]
    */
-  protected[this] def newBuilder: Builder[A, CC[A]] = companion.newBuilder[A]
+  protected[this] def newBuilder: Builder[A @uncheckedVariance, CC[A @uncheckedVariance]] = companion.newBuilder[A]
 
   /** The generic builder that builds instances of $Coll
    *  at arbitrary element types.

core/src/main/scala/scala/collection/generic/HasNewBuilder.scala

@@ -15,8 +15,9 @@ package collection
 package generic
 
 import mutable.Builder
+import scala.annotation.unchecked.uncheckedVariance
 
 trait HasNewBuilder[+A, +Repr] extends Any {
   /** The builder that builds instances of Repr */
-  protected[this] def newBuilder: Builder[A, Repr]
+  protected[this] def newBuilder: Builder[A @uncheckedVariance, Repr]
 }

core/src/main/scala/scala/collection/generic/HasNewCombiner.scala

@@ -15,8 +15,9 @@ package collection
 package generic
 
 import scala.collection.parallel.Combiner
+import scala.annotation.unchecked.uncheckedVariance
 
 trait HasNewCombiner[+T, +Repr] {
-  protected[this] def newCombiner: Combiner[T, Repr]
+  protected[this] def newCombiner: Combiner[T @uncheckedVariance, Repr]
 }