Simplify the run-time wrappers of arrays for use in varargs.

The `ScalaRunTime.wrap*Array` methods are exclusively used by the codegen for varargs. They are always called with fresh (hence non-null) arrays that are non-empty. Therefore, the various code paths handling `null`s and empty arrays were dead code. This commit removes those code paths to simplify those methods and streamline varargs call sites.

Author: sjrd

library/src/scala/runtime/ScalaRunTime.scala

@@ -274,22 +274,20 @@ object ScalaRunTime {
  case s => s + "\n"
  }
 
- // Convert arrays to immutable.ArraySeq for use with Java varargs:
- def genericWrapArray[T](xs: Array[T]): ArraySeq[T] =
- if (xs eq null) null
- else ArraySeq.unsafeWrapArray(xs)
- def wrapRefArray[T <: AnyRef](xs: Array[T]): ArraySeq[T] = {
- if (xs eq null) null
- else if (xs.length == 0) ArraySeq.empty[AnyRef].asInstanceOf[ArraySeq[T]]
- else new ArraySeq.ofRef[T](xs)
- }
- def wrapIntArray(xs: Array[Int]): ArraySeq[Int] = if (xs ne null) new ArraySeq.ofInt(xs) else null
- def wrapDoubleArray(xs: Array[Double]): ArraySeq[Double] = if (xs ne null) new ArraySeq.ofDouble(xs) else null
- def wrapLongArray(xs: Array[Long]): ArraySeq[Long] = if (xs ne null) new ArraySeq.ofLong(xs) else null
- def wrapFloatArray(xs: Array[Float]): ArraySeq[Float] = if (xs ne null) new ArraySeq.ofFloat(xs) else null
- def wrapCharArray(xs: Array[Char]): ArraySeq[Char] = if (xs ne null) new ArraySeq.ofChar(xs) else null
- def wrapByteArray(xs: Array[Byte]): ArraySeq[Byte] = if (xs ne null) new ArraySeq.ofByte(xs) else null
- def wrapShortArray(xs: Array[Short]): ArraySeq[Short] = if (xs ne null) new ArraySeq.ofShort(xs) else null
- def wrapBooleanArray(xs: Array[Boolean]): ArraySeq[Boolean] = if (xs ne null) new ArraySeq.ofBoolean(xs) else null
- def wrapUnitArray(xs: Array[Unit]): ArraySeq[Unit] = if (xs ne null) new ArraySeq.ofUnit(xs) else null
+ // Convert arrays to immutable.ArraySeq for use with Scala varargs.
+ // By construction, calls to these methods always receive a fresh (and non-null), non-empty array.
+ // In cases where an empty array would appear, the compiler uses a direct reference to Nil instead.
+ // Synthetic Java varargs forwarders (@annotation.varargs or varargs bridges when overriding) may pass
+ // `null` to these methods; but returning `null` or `ArraySeq(null)` makes little difference in practice.
+ def genericWrapArray[T](xs: Array[T]): ArraySeq[T] = ArraySeq.unsafeWrapArray(xs)
+ def wrapRefArray[T <: AnyRef](xs: Array[T]): ArraySeq[T] = new ArraySeq.ofRef[T](xs)
+ def wrapIntArray(xs: Array[Int]): ArraySeq[Int] = new ArraySeq.ofInt(xs)
+ def wrapDoubleArray(xs: Array[Double]): ArraySeq[Double] = new ArraySeq.ofDouble(xs)
+ def wrapLongArray(xs: Array[Long]): ArraySeq[Long] = new ArraySeq.ofLong(xs)
+ def wrapFloatArray(xs: Array[Float]): ArraySeq[Float] = new ArraySeq.ofFloat(xs)
+ def wrapCharArray(xs: Array[Char]): ArraySeq[Char] = new ArraySeq.ofChar(xs)
+ def wrapByteArray(xs: Array[Byte]): ArraySeq[Byte] = new ArraySeq.ofByte(xs)
+ def wrapShortArray(xs: Array[Short]): ArraySeq[Short] = new ArraySeq.ofShort(xs)
+ def wrapBooleanArray(xs: Array[Boolean]): ArraySeq[Boolean] = new ArraySeq.ofBoolean(xs)
+ def wrapUnitArray(xs: Array[Unit]): ArraySeq[Unit] = new ArraySeq.ofUnit(xs)
 }