Pre-registering certain standard classes to better support long term persistence scenarios

[gdiet]

This PR is about registering standard scala classes that are likely to be used when long term persisting data, for example in event stores:

When using kryo/chill for long term storage, it is advisable to run Kryo with setRegistrationRequired(true). However, a number of standard scala classes that are useful in such scenarios are not pre-registered in chill, most of them located in scala.collections.immutable. This has puzzled others as well, see for example the chill issue #227 which is fixed by this PR.

Some of the classes I have added to the standard registration in this pull request:

scala.None
scala.collection.immutable.::
scala.collection.immutable.Nil
scala.collection.immutable.ListSet.EmptyListSet
scala.collection.immutable.Range
scala.collection.mutable.WrappedArray.ofRef
int[]

To better support the long term persistence scenario, I have added the RegistrationIdsSpec, which will fail if the pre-registered IDs change, because changing them should be avoided if possible to ensure backwards compatibility. Or, if changing pre-registered IDs is really inevitable, a compatibility note should be added to the release notes.

If this PR is accepted, I plan to complement it with two more PRs: One PR for the chill documentation with notes on how kryo/chill can be used for long term persisting events (lessons learned). The other PR would be another spec ensuring that the binary representation of serialized classes is not changed unintendedly.

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✅ gdiet
❌ Georg Dietrich

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[gdiet]

Yes, Travis CI build failed, but :) this is because travis uses scala 2.10.6, and with scala 2.10.7 the tests run green (at least locally). So I propose that the Travis CI is reconfigured to use scala 2.10.7.

[johnynek]

@gdiet can you bump to modern scalas here:

https://github.com/twitter/chill/blob/develop/.travis.yml

then you should be green?

[johnynek]

Thanks for this PR, by the way!

[johnynek]

This looks like a great improvement. I appreciate the tests. Thank you.

[johnynek]

can you add all new items at the end of the list? Otherwise, I think we could change the tokens and some people have (ill-advisedly) persisted kryo data into long term storage.

[gdiet]

yes... I will follow your next proposal and put all new items into a separate registrar.

[johnynek]

so this test protects the future, but not people in the past right? They all get broken right?

Could we work around that? Maybe add a new registrar that people can opt in to adding?

[gdiet]

Right, this would break compatibility for projects that have already used chill for long term storage. Defining a separate registrar is OK for me (although the order of entries in the registrar will be less orderly that way).

I'm thinking along these lines currently:

• Rename AllScalaRegistrar -> AllScalaRegistrar_0_9_2 for those who need the old registrations.
• Create a new AllScalaRegistrar that first registers everything from AllScalaRegistrar_0_9_2, then registers all the new items from this PR.

Does this sound OK?

[codecov-io]

Codecov Report

Merging #302 into develop will increase coverage by 4.27%.
The diff coverage is 98.24%.

@@             Coverage Diff             @@
##           develop     #302      +/-   ##
===========================================
+ Coverage    47.86%   52.13%   +4.27%     
===========================================
  Files           41       42       +1     
  Lines         1262     1314      +52     
  Branches        38       38              
===========================================
+ Hits           604      685      +81     
+ Misses         658      629      -29

Impacted Files	Coverage Δ
...la/com/twitter/chill/ClassManifestSerializer.scala	0% <0%> (ø)	⬆️
...ain/scala/com/twitter/chill/StreamSerializer.scala	100% <100%> (ø)
...cala/com/twitter/chill/ScalaKryoInstantiator.scala	99.2% <100%> (+0.52%)	⬆️
...ain/scala/com/twitter/chill/TupleSerializers.scala	19.04% <0%> (+4.6%)	⬆️

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