Facet vs Serde flatten

README.md

https://x.com/mycoliza/status/2085090316038885461

Cargo.toml

[package]
name = "serde-facet-flatten-comparison"
version = "0.1.0"
edition = "2024"

[dependencies]
facet = "0.46.5"
facet-json = "0.46.1"
serde = { version = "1.0.229", features = ["derive"] }
serde_json = "1.0.151"

facet.ansi

serde-facet-flatten-comparison on  main [?] is 📦 v0.1.0 via 🦀 v1.96.0 took 6s 
❯ cargo run --example facet
   Compiling serde-facet-flatten-comparison v0.1.0 (G:\Programming\Repos\serde-facet-flatten-comparison)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 1.00s                                                                                                                                                                   
     Running `target\debug\examples\facet.exe`
{
  "foo": 0,
  "bar": "",
  "foo": 0,
  "baz": false,
  "baz": false,
  "quux": [
    0,
    0
  ]
}

...but does it parse?
Err(
    DeserializeError { span: [0..0), path: <root>, kind: solver error: failed to build schema: Duplicate field name 'foo' from different sources: thingy.foo vs other_thingy.foo. This usually means a parent struct and a flattened struct both define a field with the same name. },
)

facet.rs

#[derive(Debug, Default, facet::Facet)]
pub struct MyThingy {
    foo: usize,
    bar: String,
}


#[derive(Debug,  Default, facet::Facet)]
pub struct MyOtherThingy {
    foo: usize,
    baz: bool,
}

#[derive(Debug, Default, facet::Facet)]
pub struct MyThirdThingy {
    baz: bool,
    quux: (usize, usize)
}

#[derive(Debug, Default, facet::Facet)]
pub struct MyContainer {
    #[facet(flatten)]
    thingy: MyThingy,
    #[facet(flatten)]
    other_thingy: MyOtherThingy,
    #[facet(flatten)]
    third_thingy: MyThirdThingy
}

fn main() {
    let container = MyContainer::default();
    let json = facet_json::to_string_pretty(&container).unwrap();
    println!("{json}\n");
    println!("...but does it parse?");
    println!("{:#?}", facet_json::from_str::<MyContainer>(&json));

}

serde.ansi

serde-facet-flatten-comparison on  main [?] is 📦 v0.1.0 via 🦀 v1.96.0 
❯ cargo run --example serde
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.11s
     Running `target\debug\examples\serde.exe`
{
  "foo": 0,
  "bar": "",
  "foo": 0,
  "baz": false,
  "baz": false,
  "quux": [
    0,
    0
  ]
}

...but does it parse?
Err(
    Error("duplicate field `foo`", line: 11, column: 1),
)

serde.rs

use serde;
use serde_json;

#[derive(Debug, Default,  serde::Serialize, serde::Deserialize)]
pub struct MyThingy {
    foo: usize,
    bar: String,
}


#[derive(Debug,  Default, serde::Serialize, serde::Deserialize)]
pub struct MyOtherThingy {
    foo: usize,
    baz: bool,
}

#[derive(Debug, Default, serde::Serialize, serde::Deserialize)]
pub struct MyThirdThingy {
    baz: bool,
    quux: (usize, usize)
}

#[derive(Debug, Default, serde::Serialize, serde::Deserialize)]
pub struct MyContainer {
    #[serde(flatten)]
    thingy: MyThingy,
    #[serde(flatten)]
    other_thingy: MyOtherThingy,
    #[serde(flatten)]
    third_thingy: MyThirdThingy
}

fn main() {
    let container = MyContainer::default();
    let json = serde_json::to_string_pretty(&container).unwrap();
    println!("{json}\n");
    println!("...but does it parse?");
    println!("{:#?}", serde_json::from_str::<MyContainer>(&json));

}