(Custom) attributes for unions

[Christiaan Biesterbosch <kr...@apache.org>]

Hi all,

I'm running into a problem where it would be really nice to put a custom attribute on a union. For primitive types you can do:
> {
>   "type": "int",
>   "custom": 123
> }
instead of:
> "int"
to allow adding custom attributes.

But for unions doing:
> {
>   "type": ["null", "int"],
>   "custom": 123
> }
instead of:
> ["null", "int"]
results in a parse error in the Java and Python codebases but is supported in the Rust codebase (although the custom attribute is ignored there).

Is this something we should support in all codebases?

Sincerely,
Christiaan