kdl

kdl is a "document-oriented" parser and API for the KDL Document Language, a node-based, human-friendly configuration and serialization format.

Unlike serde-based implementations, this crate preserves formatting when editing, as well as when inserting or changing values with custom formatting. This is most useful when working with human-maintained KDL files.

You can think of this crate as toml_edit, but for KDL.

This crate supports both KDL v2.0.0 and v1.0.0 (when using the non-default v1 feature). It also supports converting documents between either format.

There is also a v1-fallback feature that may be enabled in order to have the various Kdl*::parse methods try to parse their input as v2, and, if that fails, try again as v1. In either case, a dedicated Kdl*::parse_v1 method is available for v1-exclusive parsing, as long as either v1 or v1-fallback are enabled.

Example

use kdl::{KdlDocument, KdlValue};

let doc_str = r#"
hello 1 2 3

// Comment
world prop=string-value {
    child 1
    child 2
    child #inf
}
"#;

let doc: KdlDocument = doc_str.parse().expect("failed to parse KDL");

assert_eq!(
    doc.iter_args("hello").collect::<Vec<&KdlValue>>(),
    vec![&1.into(), &2.into(), &3.into()]
);

assert_eq!(
    doc.get("world").map(|node| &node["prop"]),
    Some(&"string-value".into())
);

// Documents fully roundtrip:
assert_eq!(doc.to_string(), doc_str);

Controlling Formatting

By default, everything is created with default formatting. You can parse items manually to provide custom representations, comments, etc:

let node_str = r#"
  // indented comment
  "formatted" 1 /* comment */ \
    2;
"#;

let mut doc = kdl::KdlDocument::new();
doc.nodes_mut().push(node_str.parse().unwrap());

assert_eq!(&doc.to_string(), node_str);

KdlDocument, KdlNode, KdlEntry, and KdlIdentifier can all be parsed and managed this way.

Error Reporting

KdlError implements miette::Diagnostic and can be used to display detailed, pretty-printed diagnostic messages when using miette::Result and the "fancy" feature flag for miette:

# Cargo.toml
[dependencies]
miette = { version = "x.y.z", features = ["fancy"] }

fn main() -> miette::Result<()> {
    "foo 1.".parse::<kdl::KdlDocument>()?;
    Ok(())
}

This will display a message like:

Error:
  × Expected valid value.
   ╭────
 1 │ foo 1.
   ·     ─┬
   ·      ╰── invalid float
   ╰────
  help: Floating point numbers must be base 10, and have numbers after the decimal point.

Features

• span (default) - Includes spans in the various document-related structs.
• v1 - Adds support for v1 parsing. This will pull in the entire previous version of kdl-rs, and so may be fairly heavy.
• v1-fallback - Implies v1. Makes it so the various *::parse() and FromStr implementations try to parse their inputs as v2, and, if that fails, try again with v1. For KdlDocument, a heuristic will be applied if both v1 and v2 parsers fail, to pick which error(s) to return. For other types, only the v2 parser's errors will be returned.

Quirks

Properties

Multiple properties with the same name are allowed, and all duplicated will be preserved, meaning those documents will correctly round-trip. When using node.get()/node["key"] & company, the last property with that name's value will be returned (as per spec).

Numbers

KDL itself does not specify a particular representation for numbers and accepts just about anything valid, no matter how large and how small. This means a few things:

• Numbers without a decimal point are interpreted as [i128].
• Numbers with a decimal point are interpreted as [f64].
• The keywords #inf, #-inf, and #nan evaluate to [f64::INFINITY], [f64::NEG_INFINITY], and [f64::NAN].
• The original representation/text of these numbers will be preserved, unless you [KdlDocument::autoformat] in which case the original representation will be thrown away and the actual value will be used when serializing.

Minimum Supported Rust Version (MSRV)

You must be at least 1.81 tall to get on this ride.

License

The code in this repository is covered by the Apache-2.0 License.