Missing smithy-trait-codegen union support

[msosnicki]

We're using the new smithy-trait-codegen module to generate the java trait files for the protocols. Seem that the unions are not supported yet

smithy/smithy-trait-codegen/src/main/java/software/amazon/smithy/traitcodegen/TraitCodegenSymbolProvider.java

Line 184 in 1805e51

throw new UnsupportedOperationException("Union shapes are not supported at this time.");

.

Is it something on the radar for the upcoming releases? If not, would contribution speed up the process?

Thanks

[hpmellema]

We do have plans to add support for union traits in a future release.

[joelvanderhoof]

We do have plans to add support for union traits in a future release.

Will this include traits to support untagged and discriminated unions?

[hpmellema]

The support for union traits mentioned here is for generating the java implementation of custom Smithy Union traits such as:

@trait 
union MyUnion {
    option1: String 
    option2: Integer
}

I was not referring to adding additional behavior traits to modify the behavior of Smithy unions. Support for union trait generation will not include anything relating to untagged unions.

[msosnicki]

@hpmellema Will it also support the following case?

@trait
structure MyTrait {
    union: MyUnion
} 
union MyUnion {
    option1: String 
    option2: Integer
}

During decoding, it would work only for tagged unions, right? For example:

@MyTrait(
    union: {
        option1: "Foo"
    }
}
structure StructWithTrait {}

[hpmellema]

Yes, we plan to support nested unions within trait definitions, and yes, on node deserialization only tagged unions would be supported.