From e0079c4274e418720c54b5e06e08adef023d7e79 Mon Sep 17 00:00:00 2001
From: Pavel Pavlov <pavel.e.pavlov@gmail.com>
Date: Sat, 8 Feb 2014 19:34:26 +0700
Subject: SI-8251 deprecate `ListBuffer::readOnly`

This is the first step towards fixing the unexpected behavior of `ListBuffer`.

Many of `ListBuffer`'s operations are forwarded to the underlying `List`,
essentially leaking that abstraction to clients that call e.g., `toIterable`.
When the buffer changes, the `Iterable` obtained through `toIterable` will
reflect that change.

To avoid this exposure, call `toList` to obtain an immutable copy.

See also:
https://groups.google.com/d/msg/scala-internals/g_-gIWgB8Os/kWazrALbLKEJ
https://gist.github.com/paulp/9081797
---
 src/library/scala/collection/mutable/BufferLike.scala |  6 ++++--
 src/library/scala/collection/mutable/ListBuffer.scala |  5 +++--
 src/library/scala/collection/mutable/Map.scala        | 12 ------------
 test/files/run/t4288.scala                            |  2 +-
 4 files changed, 8 insertions(+), 17 deletions(-)

diff --git a/src/library/scala/collection/mutable/BufferLike.scala b/src/library/scala/collection/mutable/BufferLike.scala
index 7ba0b27ce5..3c57387c03 100644
--- a/src/library/scala/collection/mutable/BufferLike.scala
+++ b/src/library/scala/collection/mutable/BufferLike.scala
@@ -211,9 +211,11 @@ trait BufferLike[A, +This <: BufferLike[A, This] with Buffer[A]]
    */
   override def stringPrefix: String = "Buffer"
 
-  /** Provide a read-only view of this buffer as a sequence
-   *  @return  A sequence which refers to this buffer for all its operations.
+  /** Returns the current evolving(!) state of this buffer as a read-only sequence.
+   *
+   *  @return  A sequence that forwards to this buffer for all its operations.
    */
+  @deprecated("The returned sequence changes as this buffer is mutated. For an immutable copy, use, e.g., toList.", "2.11.0")
   def readOnly: scala.collection.Seq[A] = toSeq
 
   /** Creates a new collection containing both the elements of this collection and the provided
diff --git a/src/library/scala/collection/mutable/ListBuffer.scala b/src/library/scala/collection/mutable/ListBuffer.scala
index e76825cea9..5e838d0d88 100644
--- a/src/library/scala/collection/mutable/ListBuffer.scala
+++ b/src/library/scala/collection/mutable/ListBuffer.scala
@@ -13,6 +13,7 @@ package mutable
 import generic._
 import immutable.{List, Nil, ::}
 import java.io._
+import scala.annotation.migration
 
 /** A `Buffer` implementation back up by a list. It provides constant time
  *  prepend and append. Most other operations are linear.
@@ -262,7 +263,7 @@ final class ListBuffer[A]
    *  @param n         the index which refers to the first element to remove.
    *  @param count     the number of elements to remove.
    */
-  @scala.annotation.migration("Invalid input values will be rejected in future releases.", "2.11")
+  @migration("Invalid input values will be rejected in future releases.", "2.11")
   override def remove(n: Int, count: Int) {
     if (n >= len)
       return
@@ -407,7 +408,7 @@ final class ListBuffer[A]
       }
   }
 
-  /** expose the underlying list but do not mark it as exported */
+  @deprecated("The result of this method will change along with this buffer, which is often not what's expected.", "2.11.0")
   override def readOnly: List[A] = start
 
   // Private methods
diff --git a/src/library/scala/collection/mutable/Map.scala b/src/library/scala/collection/mutable/Map.scala
index fe29ce4221..2ac3cb65b5 100644
--- a/src/library/scala/collection/mutable/Map.scala
+++ b/src/library/scala/collection/mutable/Map.scala
@@ -47,18 +47,6 @@ trait Map[A, B]
    *  @return      a wrapper of the map with a default value
    */
   def withDefaultValue(d: B): mutable.Map[A, B] = new Map.WithDefault[A, B](this, x => d)
-
-  /*  Return a read-only projection of this map.  !!! or just use an (immutable) MapProxy?
-  def readOnly : scala.collection.Map[A, B] = new scala.collection.Map[A, B] {
-    override def size = self.size
-    override def update(key: A, value: B) = self.update(key, value)
-    override def - (elem: A) = self - elem
-    override def iterator = self.iterator
-    override def foreach[U](f: ((A, B)) =>  U) = self.foreach(f)
-    override def empty[C] = self.empty[C]
-    def get(key: A) = self.get(key)
-  }
-  */
 }
 
 /** $factoryInfo
diff --git a/test/files/run/t4288.scala b/test/files/run/t4288.scala
index 4e7b366f60..23319d1c27 100644
--- a/test/files/run/t4288.scala
+++ b/test/files/run/t4288.scala
@@ -1,6 +1,6 @@
 object Test {
   def f1 = scala.collection.mutable.ListBuffer(1 to 9: _*).slice(-5, -1)
-  def f2 = scala.collection.mutable.ListBuffer(1 to 9: _*).readOnly.slice(-5, -1)
+  def f2 = List(1 to 9: _*).slice(-5, -1)
   def f3 = Vector(1 to 9: _*).slice(-5, -1)
   def f4 = Traversable(1 to 9: _*).slice(-5, -1)
   def f5 = (1 to 9).toArray.slice(-5, -1)
-- 
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