Support variants with multiple fields in UDTs

[brson]

What

Add support for UDT enums with variants containing up to 12 fields.

Add more test cases.

Why

UDT enum variants are currently limited to a single field, which seems arbitrary and surprising.

Known limitations

This does not add support for struct-like variants.

The spec for tuple-like variants is now a ScpSpecUdtUnionCaseV0 of ScSpecTypeTuple:

        ScSpecUdtUnionCaseV0 {
            name: name.try_into().unwrap_or_else(|_| StringM::default()),
            type_: Some(ScSpecTypeDef::Tuple(Box::new(ScSpecTypeTuple {
                value_types: field_types,
            }))),
        }

Please consider whether this is correct. I am not sure.

This patch requires updates to rs-stellar-xdr and rs-soroban-sdk to support conversions of 13-tuples:

• Add 13-tuple conversions rs-soroban-env#658
• Add 13-tuple conversions rs-stellar-xdr#230

This patch went through a lot of iteration and ended up making a bigger diff than necessary.

cc #153

[leighmcculloch]

The spec for tuple-like variants is now a ScpSpecUdtUnionCaseV0 of ScSpecTypeTuple:

        ScSpecUdtUnionCaseV0 {
            name: name.try_into().unwrap_or_else(|_| StringM::default()),
            type_: Some(ScSpecTypeDef::Tuple(Box::new(ScSpecTypeTuple {
                value_types: field_types,
            }))),
        }

I think this will result in code generated that doens't match the original code. For example:

type Enum enum {
    Variant(A1, A2)
}

Will result inthe following being code generated:

type Enum enum {
    Variant((A1, A2))
}

So I think we need to change the XDR so that the type_ value can be a vec instead of a optional, so that it can contain one or more types.

[leighmcculloch]

The smallest diff we could make to the spec to support it is:

diff --git a/Stellar-contract-spec.x b/Stellar-contract-spec.x
index 56c3adf..d26c169 100644
--- a/Stellar-contract-spec.x
+++ b/Stellar-contract-spec.x
@@ -139,7 +139,7 @@ struct SCSpecUDTUnionCaseV0
 {
     string doc<SC_SPEC_DOC_LIMIT>;
     string name<60>;
-    SCSpecTypeDef *type;
+    SCSpecTypeDef type<12>;
 };
 
 struct SCSpecUDTUnionV0

But maybe we should make that struct a union, and explicitly distinguish between unit and tuple variants.

[leighmcculloch]

I'm making some changes to the spec xdr to support multiple tuples in the spec itself: stellar/stellar-xdr#67.

[brson]

Thanks for making the XDR changes for me.

I started upgrading rs-soroban-sdk to the latest XDR until I discovered the new doc fields, and the open questions about it in chat. Do you want me to hold off and let you deal with the SDK upgrade?

[leighmcculloch]

Sorry about that, the docs changes are in #841 which I plan to finish and need on Monday. You could base your changes on that PR though if you wanted to move ahead.

[brson]

Rebased.