return of filterKeys is not serializable

[scabug]

Return of filterKeys is not serializable. I'm not sure this is intended behaviour or a bug, but it's possible to confuse users. Attached file throws following exception:

java.io.NotSerializableException: scala.collection.immutable.MapLike$$anon$1
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1180)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1528)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1493)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:346)
at Test$delayedInit$body.apply(Test.scala:13)

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-6654?orig=1
Reporter: @ihji
Affected Versions: 2.10.0-RC2
See #4776
Attachments:

• Test.scala (created on Nov 12, 2012 4:57:21 AM UTC, 397 bytes)

[scabug]

@rklaehn said:
filterKeys and mapValues basically return views that reference the original collection and a filter predicate instead of creating an entirely new collection. So it is no wonder they are not serializable.

Fix #4776 by either returning a MapView or returning an entirely new Map, and the issue will solve itself.

[scabug]

@Blaisorblade said:
In the meantime, a more direct solution:
https://groups.google.com/d/topic/scala-internals/oso5yrKV5ds/discussion

[scabug]

@adriaanm said:
Unassigning and rescheduling to M6 as previous deadline was missed.

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Eran Medan (eranation) said (edited on Mar 7, 2015 10:11:07 AM UTC):
This causes interesting bugs when using with Spark...
Used -Dsun.io.serialization.extendedDebugInfo=true and the way to here was short
Anything I can do to help? isn't this a simple fix? (I saw some pull requests... anything wrong with them?)

[scabug]

@dragos said:
I agree it's very surprising. At least a more prominent note in Scaladoc? Would that be accepted as a PR?

[Blaisorblade]

Copying tags from #7005 since collections are being worked upon @szeiger @julienrf.