refactor: prepare serialization infrastructure for .NET 8+

[vbreuss]

This fixes #1033:
As BinaryFormatter becomes obsolete, remove the tests for serialization on .NET8.0 or greater. Also move the Serialization attribute behind a feature flag, which is currently always active, but will be disabled with .NET9.

[fgreinacher]

Just a quick answer while I'm on vacation 😎

Reading https://github.com/dotnet/designs/blob/main/accepted/2020/better-obsoletion/binaryformatter-obsoletion.md I don't see SerializableAttribute being deprecated for .NET 8. What's the reason that we have to exclude it?

[vbreuss]

Just a quick answer while I'm on vacation 😎

Reading https://github.com/dotnet/designs/blob/main/accepted/2020/better-obsoletion/binaryformatter-obsoletion.md I don't see SerializableAttribute being deprecated for .NET 8. What's the reason that we have to exclude it?

@fgreinacher
Probably we don't have to exclude it, but as this attribute only applies when using the BinaryFormatter or SoapFormatter, which both are obsolete in .NET8 I would also remove the attribute (see also here).

I can of course keep the attributes also for .NET8, but there is no way to test them anymore!

[fgreinacher]

@vbreuss If I understand the upstream documentation (especially https://github.com/dotnet/designs/blob/main/accepted/2020/better-obsoletion/binaryformatter-obsoletion.md#binaryformatter-disabled-by-default-across-all-project-types-net-8) right, applications can still opt in to binary serialization via the EnableUnsafeBinaryFormatterSerialization switch. As this library can be used in such scenarios I think we should not remove the attributes for .NET 8 and instead set the switch in our test project. WDYT?

[vbreuss]

If I understand the upstream documentation (especially https://github.com/dotnet/designs/blob/main/accepted/2020/better-obsoletion/binaryformatter-obsoletion.md#binaryformatter-disabled-by-default-across-all-project-types-net-8) right, applications can still opt in to binary serialization via the EnableUnsafeBinaryFormatterSerialization switch. As this library can be used in such scenarios I think we should not remove the attributes for .NET 8 and instead set the switch in our test project.

@fgreinacher
I interpreted this

to mean, that the attribute should no longer be used in .NET 8 or newer for custom types.
As an upgrade of the .NET version can always result in a breaking change, I preferred to remove the SerializableAttribute altogether.

However, I see your point that the workaround via EnableUnsafeBinaryFormatterSerialization is not working anymore.
I can update the pull request, to keep the attributes. However, I don't think it necessary to explicitely update the tests, and instead I would just disable the serialization tests for .NET 8 or newer.

The attribute would then be removed with .NET 9 when the BinaryFormatter infrastructure gets removed, right?

[fgreinacher]

However, I don't think it necessary to explicitely update the tests, and instead I would just disable the serialization tests for .NET 8 or newer.

I think we should keep them because we should still support the legacy serialization if applications explicitly opt-in.

The attribute would then be removed with .NET 9 when the BinaryFormatter infrastructure gets removed, right?

Yes, seems like that :)

[vbreuss]

@fgreinacher
I moved the SerializableAttribute behind a feature flag, that is currently always active. This way it will be easy to disable for a specific framework version in future.
The tests for serialization will only run pre-.NET8.

I hope this is okay with you :-)

[fgreinacher]

I moved the SerializableAttribute behind a feature flag, that is currently always active. This way it will be easy to disable for a specific framework version in future.

That's cool, thanks a lot!

The tests for serialization will only run pre-.NET8.

As mentioned above I'd prefer to add not exclude them and instead add this the test csprojs:

  <PropertyGroup>
    <!--
      Allow deprecated binary formatter functionality on .NET 8 so that we can test it
    -->
    <EnableUnsafeBinaryFormatterSerialization Condition="'$(TargetFramework)' == 'net8.0'">true</EnableUnsafeBinaryFormatterSerialization>
  </PropertyGroup>

[fgreinacher]

Thanks again @vbreuss 🙇

[github-actions]

This is addressed in release v19.2.87.