refactor: extract shared lint record primitives

crates/lint-common/src/frontmatter.rs

@@ -0,0 +1,81 @@
+//! Common frontmatter helpers.
+
+use chrono::{DateTime, Utc};
+
+use crate::RecordLintError;
+
+/// Trait record frontmatter types implement so linters can drive them uniformly.
+pub trait Frontmatter: Sized {
+    /// Hard upper bound on body chars (excluding the frontmatter block).
+    const BODY_LIMIT: usize;
+
+    fn created_at(&self) -> Option<DateTime<Utc>>;
+    fn updated_at(&self) -> Option<DateTime<Utc>>;
+}
+
+const FRONTMATTER_DELIM: &str = "---";
+
+/// Split a markdown document into `(yaml_frontmatter, body)`.
+///
+/// Expects the document to start with `---\n` and have a closing
+/// `---\n` (or `---` at EOF) somewhere downstream. Trailing newline
+/// after the closing delimiter is consumed.
+pub fn split_frontmatter(content: &str) -> Result<(&str, &str), RecordLintError> {
+    // The opening delimiter must be the very first line.
+    let after_open = content
+        .strip_prefix(FRONTMATTER_DELIM)
+        .and_then(|s| s.strip_prefix('\n').or(Some(s)))
+        .ok_or(RecordLintError::MissingFrontmatter)?;
+
+    // Look for the closing `---` on its own line.
+    let mut yaml_end = None;
+    let mut byte_offset = 0usize;
+    for line in after_open.split_inclusive('\n') {
+        let trimmed = line.trim_end_matches('\n').trim_end_matches('\r');
+        if trimmed == FRONTMATTER_DELIM {
+            yaml_end = Some((byte_offset, byte_offset + line.len()));
+            break;
+        }
+        byte_offset += line.len();
+    }
+
+    let (yaml_end_excl, body_start) = yaml_end.ok_or_else(|| {
+        RecordLintError::MalformedFrontmatter("missing closing `---` line".to_string())
+    })?;
+
+    let yaml = &after_open[..yaml_end_excl];
+    let body = &after_open[body_start..];
+    Ok((yaml, body))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn splits_simple() {
+        let doc = "---\nfoo: 1\n---\nbody here\n";
+        let (y, b) = split_frontmatter(doc).unwrap();
+        assert_eq!(y, "foo: 1\n");
+        assert_eq!(b, "body here\n");
+    }
+
+    #[test]
+    fn no_leading_delim_errors() {
+        let err = split_frontmatter("hello").unwrap_err();
+        assert!(matches!(err, RecordLintError::MissingFrontmatter));
+    }
+
+    #[test]
+    fn no_closing_delim_errors() {
+        let err = split_frontmatter("---\nfoo: 1\nno close\n").unwrap_err();
+        assert!(matches!(err, RecordLintError::MalformedFrontmatter(_)));
+    }
+
+    #[test]
+    fn handles_empty_body() {
+        let doc = "---\nfoo: 1\n---\n";
+        let (_, b) = split_frontmatter(doc).unwrap();
+        assert_eq!(b, "");
+    }
+}