derpscfg 0.4.0

# derpscfg

A brief, incomplete, and mostly wrong derive implementation for [scfg].

A fork of [scfg-rs] with simple but powerful derive capabilities.

[scfg]: https://codeberg.org/emersion/scfg
[scfg-rs]: https://sr.ht/~cdv/scfg-rs/

## Example

```rust
use derpscfg::prelude::*;

#[derive(Debug, Derpscfg)]
pub struct Model {
    #[scfg(param)]
    pub name: String,
    pub max_speed: String,
    pub weight: String,
    pub lines_served: Vec<String>,
}

#[derive(Debug, Derpscfg)]
pub struct Train {
    #[scfg(param)]
    pub name: String,
    pub model: Vec<Model>,
}

#[derive(Debug, Derpscfg)]
pub struct ScfgDemo {
    pub train: Train,
}

fn main() {

    static SCFG_DOC: &str = r#"
train "Shinkansen" {
	model "E5" {
		max-speed 320km/h
		weight 453.5t

		lines-served "Tōhoku" "Hokkaido"
	}

	model "E7" {
		max-speed 275km/h
		weight 540t

		lines-served "Hokuriku" "Jōetsu"
	}
}
"#;

    let demo = derpscfg::parse::<ScfgDemo>(SCFG_DOC).unwrap();
    println!("{demo:?}");
}
```

## Status

Can currently only derive implementations for regular struct types with named
fields. Simple enums (without fields) can be used as scalar values. No support
for tuples, newtypes, or more complex enums.

Supports parsing to most standard library types that implement `FromStr` and to
`Option`, `Vec`, `VecDeque`, and `LinkedList` of such types.

Field names with underscores are tried from both `field_name` and `field-name`.
Overriding field names is not currently implemented. Enum values can be written
in both camel or snake case.

Fields annotated with `#[scfg(param)]` are taken from a directive's parameters
in order of declaration. Be careful with cardinality. A `Vec` will always take
_all_ available params, so there can only be one, and it must be the last field
from parameters.

The toplevel `derpscfg::parse()` function can only be used on types that do not
declare any fields with `param`, as the toplevel element does not have any.

If you need the map-style genericity of scfg in parts of your data you can parse
a field to `derpscfg::Directive` (or `Option`/`Vec`/etc. thereof).

A list of _scalars_ can come from either repeated directives, or a directive
with multiple parameters, hence the following are equivalent:

```
config {
    value: 5
    value: 6
}
```

and

```
config {
    value: 5 6
}
```

Both would parse fine to a field `value: Vec<u64>`.

## Contributing

Please send patches to the [mailing list].

[mailing list]: mailto:~bitfehler/public-inbox@lists.sr.ht

## License

MIT OR Apache-2.0