8358624: ImmutableDescriptor violates equals/hashCode contract after deserialization

[kevinjwalls]

Hashcode needs to be reset to -1 to force its recalculation on next call, after deserialization.

The change in the readResolve() method is the fix for this problem. While here I added similar lines in other methods that may update fields (although these are noted as not supported, as they change a class supposedly "immutable").

Added a test. There is a test for serialization for this class, but I found it clearer to add the test for this specific recently discovered issue in its own test file.

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Issue

• JDK-8358624: ImmutableDescriptor violates equals/hashCode contract after deserialization (Bug - P4)

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[mlbridge]

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• 01: Full - Incremental (6f28e857)
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[sspitsyn]

Nit: Would it make sense to add same comment to the lines: 445, 452,473, 493?

[plummercj]

I'm not much of a serialization expert, so just asking for some clarification here. I assume when de-serialized, the initial hashcode is always 0. Why it is 0 and not by default -1. Seems this would be an issue with any de-serialized type and all would need to explicitly set to -1 as you have done in this case.