From fe9a3e9c5ef2d2de5fa62a14fa4a613a573e5e5f Mon Sep 17 00:00:00 2001
From: Jason Zaugg <jzaugg@gmail.com>
Date: Thu, 22 Aug 2013 23:51:15 +0200
Subject: SI-7269 Rework MapLike#retains to account for desugaring change

`MapLike#retains` contains a for-comprehension that relied on the strict
`filter` by its generator. You can't, in general, iterate a mutable map
and remove items in the same pass.

Here's the history of the desugaring of:

    def retain[A, B](thiz: mutable.Map[A, B])(p: (A, B) => Boolean): thiz.type = {
      thiz.foreach {
        case (k, v) =>
          if (p(k, v)) thiz -= k
      }

Before regression (c82ecabad6~1):

    thiz.filter(((check$ifrefutable$1) => check$ifrefutable$1: @scala.unchecked match {
       case scala.Tuple2((k @ _), (v @ _)) => true
       case _ => false
    })).withFilter(((x$1) => x$1: @scala.unchecked match {
       case scala.Tuple2((k @ _), (v @ _)) => p(k, v).unary_$bang
    })).foreach(((x$2) => x$2: @scala.unchecked match {
       case scala.Tuple2((k @ _), (v @ _)) => thiz.$minus$eq(k)
    }));

After regression (c82ecabad6, which incorrectly assumed in the parser that
no filter is required for isInstanceOf[Tuple2])

    thiz.withFilter(((x$1) => x$1: @scala.unchecked match {
       case scala.Tuple2((k @ _), (v @ _)) => p(k, v).unary_$bang
    })).foreach(((x$2) => x$2: @scala.unchecked match {
      case scala.Tuple2((k @ _), (v @ _)) => thiz.$minus$eq(k)
    }));

After the reversion of c82ecabad6, v2.10.2
This is also after 365bb2b4e, which uses `withFilter` rather than `filter`.

    thiz.withFilter(((check$q$1) => check$ifrefutable$1: @scala.unchecked match {
       case scala.Tuple2((k @ _), (v @ _)) => true
       case _ => false
    })).withFilter(((x$1) => x$1: @scala.unchecked match {
       case scala.Tuple2((k @ _), (v @ _)) => p(k, v).unary_$bang
    })).foreach(((x$2) => x$2: @scala.unchecked match {
      case scala.Tuple2((k @ _), (v @ _)) => thiz.$minus$eq(k)
    }));

This commit does the same as `SetLike#retains`, and converts the map to
an immutable list before the rest of the operation.
---
 src/library/scala/collection/mutable/MapLike.scala | 4 ++--
 src/library/scala/collection/mutable/SetLike.scala | 4 +++-
 2 files changed, 5 insertions(+), 3 deletions(-)

(limited to 'src')

diff --git a/src/library/scala/collection/mutable/MapLike.scala b/src/library/scala/collection/mutable/MapLike.scala
index a53aa3b76a..42e5a0a4c4 100644
--- a/src/library/scala/collection/mutable/MapLike.scala
+++ b/src/library/scala/collection/mutable/MapLike.scala
@@ -209,8 +209,8 @@ trait MapLike[A, B, +This <: MapLike[A, B, This] with Map[A, B]]
    * @param p  The test predicate
    */
   def retain(p: (A, B) => Boolean): this.type = {
-    for ((k, v) <- this.seq ; if !p(k, v))
-      this -= k
+    for ((k, v) <- this.toList) // SI-7269 toList avoids ConcurrentModificationException
+      if (!p(k, v)) this -= k
 
     this
   }
diff --git a/src/library/scala/collection/mutable/SetLike.scala b/src/library/scala/collection/mutable/SetLike.scala
index 01f87447ae..71da4c89dc 100644
--- a/src/library/scala/collection/mutable/SetLike.scala
+++ b/src/library/scala/collection/mutable/SetLike.scala
@@ -120,7 +120,9 @@ trait SetLike[A, +This <: SetLike[A, This] with Set[A]]
    *             which `p` returns `true` are retained in the set; all others
    *             are removed.
    */
-  def retain(p: A => Boolean): Unit = for (elem <- this.toList) if (!p(elem)) this -= elem
+  def retain(p: A => Boolean): Unit =
+    for (elem <- this.toList) // SI-7269 toList avoids ConcurrentModificationException
+      if (!p(elem)) this -= elem
 
   /** Removes all elements from the set. After this operation is completed,
    *  the set will be empty.
-- 
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