Merge commit '3c7d27cbac' into merge-2.12-to-2.13-aug-7

Author: lrytz

library/src/scala/collection/mutable/ArrayBuilder.scala

@@ -98,9 +98,9 @@ object ArrayBuilder {
     protected var elems: Array[T] = _
 
     private def mkArray(size: Int): Array[T] = {
-      val newelems = new Array[T](size)
-      if (this.size > 0) Array.copy(elems, 0, newelems, 0, this.size)
-      newelems
+      if (capacity == size && capacity > 0) elems
+      else if (elems eq null) new Array[T](size)
+      else java.util.Arrays.copyOf[T](elems, size)
     }
 
     protected[this] def resize(size: Int): Unit = {