Support suppressed property when deserializing Throwable

[klaasdellschaft]

Hi,

when using Jackson 2.12.x in my project to serialize / deserialize instances of Throwable, I noticed that the serialized JSON output contains the suppressed property. This property is also successfully filled in JSON if the original Throwable has suppressed exceptions. However, when deserializing the JSON back again to a cloned Throwable then this property is getting ignored, i.e. the cloned instance has an empty array of suppressed exceptions.

When debugging this issue, I think I narrowed it down to BeanDeserializerFactory.buildThrowableDeserializer(...) where the suppressed property is added to the ignorable properties.

// Java 7 also added "getSuppressed", skip if we have such data:
builder.addIgnorable("suppressed");

Based on the comment, I guess this ignoring of the suppressed property has historic reasons because it was only introduced in JDK 7, and only since jackson-databind 2.7 the Minimum JDK version is 1.7.

Given that the Minimum JDK version is even 1.8 since jackson-databind 2.12, what is your opinion on introducing deserialization support for the suppressed property? If you agree that this support should be introduced, I would give it a try to introduce it in BeanDeserializerFactory.buildThrowableDeserializer(...) and then send you a pull request. Most likely, I would implement it in a style similar to how the cause property of Throwable gets deserialized, i.e. I would add a manually constructed SettableBeanProperty that is using Throwable.addSuppressed(...) for adding the suppressed exceptions to the Throwable instance.

[cowtowncoder]

Ah. Yes, your reading of code and history is spot on.

Jackson JDK baseline for building has been JDK 8 for a bit, but 2.12 is still officially JDK7 compliant for runtime.
However, 2.13 will move the baseline fully to JDK 8 so this would be possible to add -- and due to possible complications I would like the patch against 2.13 anyway.

So, PR would be welcome, and I can help with it. I think this would be a great improvement.
The way ThrowableDeserializer is implemented is not optimal, so there may be some gotchas (wrt delegation), but I think this would be doable.

[klaasdellschaft]

Hi @cowtowncoder I would be happy if you can give me feedback on the PR. The implementation is finished, and all tests are passing.

[cowtowncoder]

Thanks! Will do -- will be out for a couple of days, will review once I get back!