Macro derive_serde_raw

macro_rules! derive_serde_raw {
    {
    $( #[ $($attrs:meta)* ] )*
    $vis:vis struct $main:ident=$main_s:literal
    $($body:tt)*
} => { ... };
}

Helper for defining a struct which can be (de)serialized several ways, including “natively”

Ideally we would have

#[derive(Deserialize)]
#[serde(try_from=Possibilities)]
struct Main { /* principal definition */ }

#[derive(Deserialize)]
#[serde(untagged)]
enum Possibilities { Main(Main), Other(OtherRepr) }

#[derive(Deserialize)]
struct OtherRepr { /* other representation we still want to read */ }

impl TryFrom<Possibilities> for Main { /* ... */ }

But the impl for Possibilities ends up honouring the try_from on Main so is recursive.

We solve that (ab)using serde’s remote feature, on a second copy of the struct definition.

See the Example for instructions. It is important to add test cases for all the representations you expect to parse and serialise, since there are easy-to-write bugs, for example omitting some of the necessary attributes.

Generated output:

• The original struct definition, unmodified
• #[derive(Serialize, Deserialize)] struct $main_Raw { }

The $main_Raw struct ought not normally be to constructed anywhere, and isn’t convertible to or from the near-identical $main struct. It exists only as a thing to feed to the serde remove derive, and name in with=.

Example

use serde::{Deserialize, Serialize};
use tor_basic_utils::derive_serde_raw;

derive_serde_raw! {
    #[derive(Deserialize, Serialize, Default, Clone, Debug)]
    #[serde(try_from="BridgeConfigBuilderSerde", into="BridgeConfigBuilderSerde")]
    pub struct BridgeConfigBuilder = "BridgeConfigBuilder" {
        transport: Option<String>,
        //...
    }
}

#[derive(Serialize,Deserialize)]
#[serde(untagged)]
enum BridgeConfigBuilderSerde {
    BridgeLine(String),
    Dict(#[serde(with="BridgeConfigBuilder_Raw")] BridgeConfigBuilder),
}

impl TryFrom<BridgeConfigBuilderSerde> for BridgeConfigBuilder { //...
impl From<BridgeConfigBuilder> for BridgeConfigBuilderSerde { //...