XDR Enums customize variants

[Arkweid]

I have a question about Enum variants. Default case works perfectly:

#[derive(Copy, Clone, Debug, Eq, PartialEq, Deserialize, Serialize)]
pub enum SignerKey {
    SIGNER_KEY_TYPE_ED25519(uint256),       // match with "0"
    SIGNER_KEY_TYPE_PRE_AUTH_TX(uint256),   // match with "1"
    SIGNER_KEY_TYPE_HASH_X(uint256),        // match with "2"
}

#[derive(Copy, Clone, Debug, Eq, PartialEq, Serialize_repr, Deserialize_repr)]
#[repr(i32)]
pub enum SignerKeyType {
    SIGNER_KEY_TYPE_ED25519 = 0,
    SIGNER_KEY_TYPE_PRE_AUTH_TX = 1,
    SIGNER_KEY_TYPE_HASH_X = 2,
}

But sometimes we have unusual Enums, something like that:

pub enum SignerKeyType {
    SIGNER_KEY_TYPE_ED25519 = 2,
    SIGNER_KEY_TYPE_PRE_AUTH_TX = 5,
    SIGNER_KEY_TYPE_HASH_X = -6,
}

Of course this doesn`t works and we cant match received values with SignerKey variants. Do we have any ability to mark it explicit? Something about that in my mind:

pub enum SignerKey {
    #[serde(compare_with = SignerKeyType::SIGNER_KEY_TYPE_PRE_AUTH_TX)] 
    SIGNER_KEY_TYPE_ED25519(uint256),   // match with "2"

    #[serde(compare_with = SignerKeyType::SIGNER_KEY_TYPE_ED25519)]
    SIGNER_KEY_TYPE_PRE_AUTH_TX(uint256),   // match with "5"

    #[serde(compare_with = SignerKeyType::SIGNER_KEY_TYPE_HASH_X)]
    SIGNER_KEY_TYPE_HASH_X(uint256),   // match with "-6"

   #[serde(default_case)]
    Void,  // pick this if previous variants doesn`t match
}

[jvff]

This is an interesting scenario. Currently, there's no way to do it, unfortunately :(

The attribute tags you suggest are interesting, but I think they might be better integrated directly into serde itself or into a separate crate.

This issue is (loosely) related to #2, which unfortunately I haven't look into for a while. I'll try to give it more thought in the coming days to see if I can come up with a solution.

[Arkweid]

That would be great! Thank you.

[jvff]

Sorry for taking so long, had a lot less free time than expected 😓

I've created a separate serde-enum crate that fulfills this purpose. In theory, all you have to do is something like:

use serde_enum::{DeserializeEnum, SerializeEnum};

const ID: u32 = 10;

#[derive(SerializeEnum, DeserializeEnum)]
enum MyEnum {
    Zero,
    One,
    Five = 5,
    Six,
    #[serde_enum(variant_id = ID)]
    Ten,
    Eleven,
}

Currently, a separate version of serde-xdr is also required, so your Cargo.toml might look something like:

[dependencies]
serde = "1.0"
serde-enum = { git = "https://github.com/jvff/serde-enum.git" }
serde-xdr = { git = "https://github.com/jvff/serde-xdr.git", branch = "ignore-enum-variant-names-feature", features = ["ignore-enum-variant-names"] }

Let me know if it works and what you think of the solution! :D

[Arkweid]

Awesome! I'll try it as soon as possible and let you to know how it going.

[Arkweid]

@jvff
I got this error:

error[E0277]: the trait bound `syn::expr::ExprParen: syn::parse::Parse` is not satisfied
  --> /home/arkweid/.cargo/git/checkouts/serde-enum-1c210c901382ad9b/54aefe3/src/lib.rs:81:39
   |
81 |     let expression: ExprParen = input.parse()?;
   |                                       ^^^^^ the trait `syn::parse::Parse` is not implemented for `syn::expr::ExprParen`

My case: https://github.com/astroband/astrocore/pull/18/files
Did I do something wrong?

[jvff]

To fix that, I had to push some commits that fix Cargo.toml with the correct syn version that's needed. You might need to run cargo update -p syn and cargo update -p serde-enum to get the latest versions.

Also, I noticed that the test enum is using #[derive(Serialize, Deserialize)]. You'd have to change it to #[derive(SerializeEnum, DeserializeEnum)] for the serde_enum attributes to be parsed.

[Arkweid]

Thank you for quick ansver, @jvff it's awesome!
I updated my case as you said, and got a lot compile errors:

error[E0425]: cannot find value `seralizer` in this scope
    --> src/xdr.rs:2061:56
     |
2061 | #[derive(Clone, Debug, Eq, PartialEq, DeserializeEnum, SerializeEnum)]
     |                                                        ^^^^^^^^^^^^^ help: a local variable with a similar name exists: `serializer`

error[E0599]: no method named `new_type_variant` found for type `<V as xdr::serde::de::EnumAccess<'de>>::Variant` in the current scope
    --> src/xdr.rs:2061:39
     |
2061 | #[derive(Clone, Debug, Eq, PartialEq, DeserializeEnum, SerializeEnum)]
     |                                       ^^^^^^^^^^^^^^^

error[E0308]: mismatched types
    --> src/xdr.rs:2061:56
     |
2061 | #[derive(Clone, Debug, Eq, PartialEq, DeserializeEnum, SerializeEnum)]
     |                                                        ^^^^^^^^^^^^^ expected struct `xdr::Error`, found reference
     |
     = note: expected type `xdr::Error`
                found type `&'static str`

[jvff]

Apparently there were a few bugs :( I thought I tested it, but apparently I only tested a very small sample of cases. I need to write some proper test cases, but I don't have much free time at the moment. As soon as I can I'll write some tests and also some documentation.

I also noticed that deserialization of enum variants with multiple fields might be unimplemented. If you end up needing that let me know and I'll try to implement it late next week.

In the mean-time, hopefully the new fixes should be enough :) Just run cargo update -p serde-enum and it should build normally afterwards. Let me know if any other issue appears.

Thanks for reporting the issues!

[Arkweid]

@jvff Great, it compiles! Serialization process works as expected, but looks like deserialization proccess still need some attention.
My case https://github.com/astroband/astrocore/blob/78813e55d82173fe0fac6325a4842bfe56e4a820/src/xdr.rs#L2061-L2077
When I run deserializetion test it failed with error:

Err(CompatDeserializationError(Compat { error: Custom { message: "unknown variant `? (discriminator is 8)`, expected one of `Error`, `Hello`, `Auth`, `DontHave`, `GetPeers`, `Peers`, `TxSetHash`, `TxSet`, `Transaction`, `QSetHash`, `QSet`, `Envelope`, `GetScpLedgerSeq`, `Void`" } }))

[jvff]

Sorry for taking so long to respond. If I understood correctly, that error appeared when running the astrocore tests. The issue is that the Hello variant is set to the ID 13, and all other variants have IDs that start counting up from that, so for example Auth becomes 14 and DontHave becomes 15.

I think the intended behaviour would be to move Hello to the end of the variants and set Auth to be represented by the variant ID 2. At least I think that this has fixed the tests.

Let me know if I missed something or if there are more issues :)

[Arkweid]

Ye, this variant works. Thank you :)
Is I still need this one?

serde-xdr = { git = "https://github.com/jvff/serde-xdr.git", branch = "ignore-enum-variant-names-feature", features = ["ignore-enum-variant-names"] }

[jvff]

Yes, that's still needed. I'll try to publish a new version soon, but I'll probably keep the feature as optional, in order to keep the previous behavior as the default one.

I'll also push serde-enum to crates.io, so that it's easier to use. But before that I'll add some documentation and tests, so it might take a while.

[Arkweid]

Oke, I'am fine with it :)