Render YAML front matter as a yaml code block#58
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Markdown files with `---` delimited front matter were rendered as two
horizontal rules with the keys/values bleeding through as paragraph text,
because comrak's front_matter_delimiter option wasn't enabled and there
was no match arm for NodeValue::FrontMatter.
- Enable options.extension.front_matter_delimiter = Some("---")
- Extract emit_code_block() out of the CodeBlock arm so both fenced code
blocks and front matter share the framed/highlighted rendering path
- Add a NodeValue::FrontMatter arm that strips the `---` delimiters and
emits a yaml code block via the shared helper
Front matter is detected positionally (must start at line 1, must have a
matching `\n---\n` closing delimiter), so a `---` elsewhere in a document
still renders as a horizontal rule. Locked in by tests:
- front_matter_renders_as_yaml_code_block (happy path)
- horizontal_rule_in_body_still_renders_as_thematic_break
- dashes_after_blank_line_are_not_front_matter
- unclosed_front_matter_falls_back_to_normal_parsing
- strip_front_matter_delimiters_handles_unix_and_windows_endings
Closes #51.
This was referenced May 14, 2026
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Summary
Closes #51. Markdown files with
---delimited front matter were rendered as two horizontal rules with the keys/values bleeding through as paragraph text — the comrakfront_matter_delimiteroption wasn't enabled and there was no match arm forNodeValue::FrontMatter.Changes:
options.extension.front_matter_delimiter = Some(\"---\")increate_options().emit_code_block()out of the existingNodeValue::CodeBlockarm so both fenced code blocks and front matter share the framed-and-highlighted rendering path.NodeValue::FrontMatterarm that strips the---delimiters (viastrip_front_matter_delimiters) and emits ayamlcode block via the shared helper. Lazy syntax highlighting picks up theyamllabel automatically.Detection contract
Front matter is detected positionally by comrak: the document must start with
---\non line 1, and a matching\n---\nmust appear later. Otherwise the---falls back to a thematic break / horizontal rule. Locked in by these tests:test_front_matter_renders_as_yaml_code_block— happy path: keys land in the code block, no horizontal rules, frame is labeledyaml, body heading still renderstest_horizontal_rule_in_body_still_renders_as_thematic_break— a---mid-document is still a horizontal ruletest_dashes_after_blank_line_are_not_front_matter— a blank line before---disqualifies ittest_unclosed_front_matter_falls_back_to_normal_parsing— missing closing delimiter falls back to default parsingtest_strip_front_matter_delimiters_handles_unix_and_windows_endings— unit test for the delimiter strip helper across\nand\r\nNote on PR #52
The vivainio draft PR #52 proposed essentially the same approach a month ago. I wrote this independently after the user asked for a fix in #51; we can close #52 once this lands.
Test plan
cargo fmt --checkcargo clippy -- -D warnings(pinned Rust 1.95.0)cargo test— 632 tests pass/tmp/test_frontmatter.md(jekyll-style file with title/author/date/tags)