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|
//! YAML frontmatter parsing for `SKILL.md` files.
//!
//! Extracts the YAML block between `---` delimiters and parses it with
//! `yaml-rust2`. Returns the parsed fields and the byte offset where the
//! body begins (after the closing `---`).
use yaml_rust2::YamlLoader;
/// Parsed frontmatter fields from a `SKILL.md` file.
#[derive(Debug, Default)]
pub(crate) struct Frontmatter {
pub name: Option<String>,
pub description: Option<String>,
pub disable_model_invocation: bool,
}
/// Result of splitting a skill file into frontmatter + body.
#[derive(Debug)]
pub(crate) struct ParsedSkillFile {
pub frontmatter: Frontmatter,
/// Everything after the closing `---` delimiter.
pub body: String,
}
/// Parse a `SKILL.md` file's content into frontmatter and body.
///
/// If no frontmatter delimiters are found, all content is treated as body
/// with default frontmatter.
pub(crate) fn parse(content: &str) -> ParsedSkillFile {
let Some((yaml_str, body)) = split_frontmatter(content) else {
return ParsedSkillFile {
frontmatter: Frontmatter::default(),
body: content.to_string(),
};
};
let frontmatter = match YamlLoader::load_from_str(yaml_str) {
Ok(docs) if !docs.is_empty() => extract_fields(&docs[0]),
Ok(_) => Frontmatter::default(),
Err(e) => {
tracing::warn!("Failed to parse skill frontmatter: {e}");
Frontmatter::default()
}
};
ParsedSkillFile { frontmatter, body }
}
/// Split content on `---` delimiters. Returns `(yaml_str, body)` or `None`
/// if frontmatter is not present.
fn split_frontmatter(content: &str) -> Option<(&str, String)> {
let trimmed = content.trim_start();
// Must start with `---`
if !trimmed.starts_with("---") {
return None;
}
// Find the end of the opening delimiter line
let after_open = trimmed.get(3..)?.trim_start_matches(|c: char| c != '\n');
let after_open = after_open.strip_prefix('\n').unwrap_or(after_open);
// Find the closing `---`
let close_pos = after_open
.lines()
.enumerate()
.find(|(_, line)| line.trim() == "---")
.map(|(i, _)| {
after_open
.lines()
.take(i)
.map(|l| l.len() + 1) // +1 for newline
.sum::<usize>()
})?;
let yaml_str = &after_open[..close_pos];
let rest = &after_open[close_pos..];
// Skip the closing `---` line
let body = rest
.strip_prefix("---")
.unwrap_or(rest)
.trim_start_matches(|c: char| c != '\n');
let body = body.strip_prefix('\n').unwrap_or(body);
Some((yaml_str, body.to_string()))
}
fn extract_fields(doc: &yaml_rust2::Yaml) -> Frontmatter {
use yaml_rust2::Yaml;
let name = match &doc["name"] {
Yaml::String(s) => Some(s.clone()),
_ => None,
};
let description = match &doc["description"] {
Yaml::String(s) => Some(s.trim().to_string()),
_ => None,
};
let disable_model_invocation = match &doc["disable-model-invocation"] {
Yaml::Boolean(b) => *b,
Yaml::String(s) => matches!(s.as_str(), "true" | "yes" | "1"),
_ => false,
};
Frontmatter {
name,
description,
disable_model_invocation,
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn basic_frontmatter() {
let content = "\
---
name: my-skill
description: A test skill
disable-model-invocation: true
---
Body content here.
";
let parsed = parse(content);
assert_eq!(parsed.frontmatter.name.as_deref(), Some("my-skill"));
assert_eq!(
parsed.frontmatter.description.as_deref(),
Some("A test skill")
);
assert!(parsed.frontmatter.disable_model_invocation);
assert_eq!(parsed.body.trim(), "Body content here.");
}
#[test]
fn multiline_folded_description() {
let content = "\
---
name: release
description: >
Orchestrate a multi-step release — version bumping, changelog
generation, PR creation, tagging, and publishing.
disable-model-invocation: true
---
# Release steps
";
let parsed = parse(content);
assert_eq!(parsed.frontmatter.name.as_deref(), Some("release"));
let desc = parsed.frontmatter.description.unwrap();
assert!(desc.contains("Orchestrate a multi-step release"));
assert!(desc.contains("publishing"));
assert!(parsed.frontmatter.disable_model_invocation);
assert!(parsed.body.contains("# Release steps"));
}
#[test]
fn no_frontmatter() {
let content = "Just a body with no frontmatter.";
let parsed = parse(content);
assert!(parsed.frontmatter.name.is_none());
assert!(parsed.frontmatter.description.is_none());
assert!(!parsed.frontmatter.disable_model_invocation);
assert_eq!(parsed.body, content);
}
#[test]
fn empty_frontmatter() {
let content = "\
---
---
Body after empty frontmatter.
";
let parsed = parse(content);
assert!(parsed.frontmatter.name.is_none());
assert!(parsed.frontmatter.description.is_none());
assert_eq!(parsed.body.trim(), "Body after empty frontmatter.");
}
#[test]
fn missing_fields_use_defaults() {
let content = "\
---
name: partial
---
Some body.
";
let parsed = parse(content);
assert_eq!(parsed.frontmatter.name.as_deref(), Some("partial"));
assert!(parsed.frontmatter.description.is_none());
assert!(!parsed.frontmatter.disable_model_invocation);
}
#[test]
fn unknown_fields_ignored() {
let content = "\
---
name: my-skill
future-field: some value
another: 42
---
Body.
";
let parsed = parse(content);
assert_eq!(parsed.frontmatter.name.as_deref(), Some("my-skill"));
}
#[test]
fn body_with_triple_dashes() {
let content = "\
---
name: test
---
Some body.
---
More body after a horizontal rule.
";
let parsed = parse(content);
assert_eq!(parsed.frontmatter.name.as_deref(), Some("test"));
assert!(parsed.body.contains("Some body."));
assert!(parsed.body.contains("More body after a horizontal rule."));
}
}
|
