vector of vectors produces invalid toml with trailing comma

[anthrotype]

I would like to use toml to serialise/deserialize a struct that contains a Vec<Vec>, however when I try that I get toml that is invalid and cannot be parsed back into a struct. See the code below, how the toml string gets serialized without errors however when I attempt to parse it it fails with

Compiling playground v0.0.1 (/playground)
    Finished dev [unoptimized + debuginfo] target(s) in 6.85s
     Running `target/debug/playground`
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Error { inner: ErrorInner { kind: Wanted { expected: "a table key", found: "a comma" }, line: Some(49), col: 0, at: Some(485), message: "", key: [] } }', src/main.rs:51:40
note: [run with `RUST_BACKTRACE=1` environment variable to display a backtrace](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=a4fdfa8f7a9fe94e94c4662e975f971b#)

use serde::{Deserialize, Serialize};

#[derive(Deserialize, Serialize, Debug)]
struct Glyph {
    components: Vec<Component>,
    // contours is a vector of vectors of points
    contours: Vec<Contour>,
}

#[derive(Deserialize, Serialize, Debug)]
struct Point {
    x: f64,
    y: f64,
    pt_type: String,
}

type Contour = Vec<Point>;

#[derive(Deserialize, Serialize, Debug)]
struct Component {
    base: String,
    transform: (f64, f64, f64, f64, f64, f64),
}

fn main() {
    let comp1 = Component { base: "b".to_string(), transform:  (1.0, 0.0, 0.0, 1.0, 0.0, 0.0) };
    let comp2 = Component { base: "c".to_string(), transform:  (1.0, 0.0, 0.0, 1.0, 0.0, 0.0) };
    let components = vec![comp1, comp2];
    
    let contours = vec![
        vec![
            Point { x: 3.0, y: 4.0, pt_type: "line".to_string() },
            Point { x: 5.0, y: 6.0, pt_type: "line".to_string() },
        ],
        vec![
            Point { x: 0.0, y: 0.0, pt_type: "move".to_string() },
            Point { x: 7.0, y: 9.0, pt_type: "offcurve".to_string() },
            Point { x: 8.0, y: 10.0, pt_type: "offcurve".to_string() },
            Point { x: 11.0, y: 12.0, pt_type: "curve".to_string() },
        ],
    ];
    let g1 = Glyph { contours, components };

    let s = toml::to_string_pretty(&g1).unwrap();
    // the vector of vectors contains a stray trailing comma at the end, making it
    // invalid toml
    println!("{}", s);
    // in fact, toml fails with inner error, { expected: "a table key", found: "a comma" }
    // at line 49, col 0
    let g2: Glyph = toml::from_str(&s).unwrap();
    println!("{:?}", g2);

https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=57b8b8d804328548b40d24dd4a5b8ae7

Am I doing something wrong? Is it possible to have an array of arrays of tables in toml, like you can say in json or yaml?

[epage]

toml does not support arbitrary structures like json or yaml; I do not think Vec<Vec<Table>> is supported for standard tables but would be for inline tables.

What results do you get using toml_edit::easy (cargo add toml_edit -F easy)? We expect to move tom;s parser/generator to use toml_edit (see #340). If toml_edit::easy works for you, that could be a workaround until we make that change.

[anthrotype]

thanks! I tried to replace it with toml_edit::easy and indeed it works, i.e. gives me array of arrays of inline tables for the Points. I'll try use that for now.