From 08869ef7c62b8caf68f2d5b6507ff445a1b79e6d Mon Sep 17 00:00:00 2001
From: Johannes Rudolph <johannes.rudolph@gmail.com>
Date: Thu, 25 Jun 2020 10:41:17 +0200
Subject: [PATCH] actor: simplify empty ByteString instances (#29268)

* actor: simplify empty ByteString instances
* use Array.emptyByteArray
---
 .../simplify-ByteString-empty.excludes               |  2 ++
 .../src/main/scala-2.13/akka/util/ByteString.scala   | 12 ++++++------
 2 files changed, 8 insertions(+), 6 deletions(-)
 create mode 100644 akka-actor/src/main/mima-filters/2.6.6.backwards.excludes/simplify-ByteString-empty.excludes

diff --git a/akka-actor/src/main/mima-filters/2.6.6.backwards.excludes/simplify-ByteString-empty.excludes b/akka-actor/src/main/mima-filters/2.6.6.backwards.excludes/simplify-ByteString-empty.excludes
new file mode 100644
index 0000000000..73ce6c428e
--- /dev/null
+++ b/akka-actor/src/main/mima-filters/2.6.6.backwards.excludes/simplify-ByteString-empty.excludes
@@ -0,0 +1,2 @@
+# removed private auxiliary constructor
+ProblemFilters.exclude[DirectMissingMethodProblem]("akka.util.ByteString#ByteString1.this")
diff --git a/akka-actor/src/main/scala-2.13/akka/util/ByteString.scala b/akka-actor/src/main/scala-2.13/akka/util/ByteString.scala
index e6009e1f0f..b63270394f 100644
--- a/akka-actor/src/main/scala-2.13/akka/util/ByteString.scala
+++ b/akka-actor/src/main/scala-2.13/akka/util/ByteString.scala
@@ -142,10 +142,10 @@ object ByteString {
    */
   def fromByteBuffer(buffer: ByteBuffer): ByteString = apply(buffer)
 
-  val empty: ByteString = CompactByteString(Array.empty[Byte])
+  def empty: ByteString = ByteString1C.empty
 
   /** Java API */
-  val emptyByteString: ByteString = empty
+  def emptyByteString: ByteString = empty
 
   def newBuilder: ByteStringBuilder = new ByteStringBuilder
 
@@ -158,6 +158,8 @@ object ByteString {
   //   }
 
   private[akka] object ByteString1C extends Companion {
+    val empty = new ByteString1C(Array.emptyByteArray)
+
     def fromString(s: String): ByteString1C = new ByteString1C(s.getBytes)
     def apply(bytes: Array[Byte]): ByteString1C = new ByteString1C(bytes)
     val SerializationIdentity = 1.toByte
@@ -273,7 +275,7 @@ object ByteString {
 
   /** INTERNAL API: ByteString backed by exactly one array, with start / end markers */
   private[akka] object ByteString1 extends Companion {
-    val empty: ByteString1 = new ByteString1(Array.empty[Byte])
+    val empty: ByteString1 = new ByteString1(Array.emptyByteArray, 0, 0)
     def fromString(s: String): ByteString1 = apply(s.getBytes)
     def apply(bytes: Array[Byte]): ByteString1 = apply(bytes, 0, bytes.length)
     def apply(bytes: Array[Byte], startIndex: Int, length: Int): ByteString1 =
@@ -293,8 +295,6 @@ object ByteString {
       extends ByteString
       with Serializable {
 
-    private def this(bytes: Array[Byte]) = this(bytes, 0, bytes.length)
-
     def apply(idx: Int): Byte = bytes(checkRangeConvert(idx))
 
     // Avoid `iterator` in performance sensitive code, call ops directly on ByteString instead
@@ -1024,7 +1024,7 @@ object CompactByteString {
     }
   }
 
-  val empty: CompactByteString = ByteString.ByteString1C(Array.empty[Byte])
+  def empty: CompactByteString = ByteString.ByteString1C.empty
 }
 
 /**