Non deterministic compiler output of WrappedString.scala which features Predef unimport

[retronym]

Since scala/scala@ea470f7, which includes:

--- a/src/library/scala/collection/immutable/WrappedString.scala
+++ b/src/library/scala/collection/immutable/WrappedString.scala
@@ -14,6 +14,7 @@ package scala.collection
 package immutable

 import mutable.{Builder, StringBuilder}
+import scala.Predef.{ wrapString => _ }  // unimport to avoid triggering accidentally

... comparing compilation results of src/library/**/*.scala in sorted and reverse sorted order shows this variation:

diff --git a/scala/collection/immutable/WrappedString.class.scalap b/scala/collection/immutable/WrappedString.class.scalap
index 1c41b6b..303d58f 100644
--- a/scala/collection/immutable/WrappedString.class.scalap
+++ b/scala/collection/immutable/WrappedString.class.scalap
@@ -2,7 +2,7 @@
 @scala.SerialVersionUID { val value = 3None }
 final class WrappedString extends scala.collection.immutable.AbstractSeq[scala.Char] with scala.collection.immutable.IndexedSeq[scala.Char] with scala.collection.immutable.IndexedSeqOps[scala.Char, scala.collection.immutable.IndexedSeq, scala.collection.immutable.WrappedString] with scala.Serializable {
   private val self: java.lang.String = { /* compiled code */ }
-  def this(self: scala.Predef.String) = { /* compiled code */ }
+  def this(self: java.lang.String) = { /* compiled code */ }
   def apply(i: scala.Int): scala.Char = { /* compiled code */ }

FTR, I bisected to this point with:

 (set rmstarsilent; sbt clean dist/mkQuick && (rm -rf /tmp/out1/* /tmp/out2/*; true) && qscalac -J-Xmx1G -d /tmp/out1 $(find src/library -name '*.scala' | sort) && qscalac -J-Xmx1G -d /tmp/out2 $(find src/library -name '*.scala' | sort -r) && jardiff /tmp/out1 /tmp/out2 | less )

[som-snytt]

That's a good one. I remember the old unimport mechanism was restrictive, but that the new one, which "registers" the import when it completes it, could suffer from ordering effects, but I was thinking part of a file sees predef and the rest does not. The question was whether to require the magic import at the top of the file.

[retronym]

WIP: #11867

[retronym]

Not a blocker for 2.13.2 IMO but I'll submit a PR for consideration.

[SethTisue]

(also not a blocker for 2.13.3? or...?)

[som-snytt]

The title says it's a feature!