[Example] Attaching source code to diagnostic while supporting different labels

[adamnejm]

Heya, I'm learning Rust and it took me quite a while to figure out the proper way to structure my errors and how to attach source_code on bubble up while supporting different labels.

Not sure if this is the best approach, but it's exactly what I wanted.
Just gonna leave this my fellow newbies :)

use kdl::KdlError;
use thiserror::Error as ThisError;
use miette::{Diagnostic, SourceSpan, NamedSource};

///////////////////////////////////////////

#[derive(Debug, ThisError, Diagnostic)]
#[error("general error")]
pub enum Error {
	#[error(transparent)]
	Io(#[from] std::io::Error),
	
	Config(ConfigError),
}

#[derive(Debug, ThisError, Diagnostic)]
#[error("config error")]
pub enum ConfigError {
	#[diagnostic(transparent)]
	Kdl(#[from] KdlError),
	
	#[error("{0} doesn't exist!")]
	NotFound(String),
	
	Contextual {
		#[source_code]
		document: NamedSource<String>,
		
		#[diagnostic_source]
		context: ParseError,
	}
}

#[derive(Debug, ThisError, Diagnostic)]
pub enum ParseError {
	#[error("unknown command")]
	UnknownCommand {
		#[label("this command doesn't exist")]
		location: SourceSpan,
	},
	
	#[error("invalid value provided")]
	InvalidValue {
		#[label("expected {expected}")]
		location: SourceSpan,
		expected: String,
	}
}

impl ParseError {
	pub fn with_document(self, name: &str, contents: String) -> ConfigError {
		ConfigError::Contextual {
			context: self,
			document: NamedSource::new(name, contents),
		}
	}
}

///////////////////////////////////////////

pub fn config_new() -> Result<(), ConfigError> {
	let filepath = "config.kdl";
	let contents = config_load()?;
	config_parse().map_err(|e| {
		e.with_document(filepath, contents)
	})
}

fn config_load() -> Result<String, ConfigError> {
	if true {
		Ok(r#"settings { my-setting: "hello!" }"#.into())
	} else {
		Err(ConfigError::NotFound("config.kdl".into()))
	}
}

fn config_parse() -> Result<(), ParseError> {
	Err(ParseError::InvalidValue {
		expected: "boolean".into(),
		location: (23..31).into(),
	})
}

fn main() -> miette::Result<()> {
    config_new()?;
    Ok(())
}