base_markdown/
code_fence.rs

1// Released under the MIT License.
2// Copyright, 2026, by Samuel Williams.
3
4/// Opening fence metadata, matching Markly's `Node::Fence` structure.
5///
6/// This describes the source opening fence. The closing fence can be longer
7/// or absent for ordinary code blocks. Markdown serialization may use a
8/// different fence according to its formatting options and content safety.
9#[derive(Clone, Copy, Debug, Eq, PartialEq)]
10#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
11pub struct CodeFence {
12    /// Fence marker: a backtick or tilde for code, or a dash/plus for frontmatter.
13    pub character: char,
14    /// Number of markers in the opening fence.
15    pub length: usize,
16    /// Opening indentation in columns, relative to the containing block.
17    /// Container markers and their required whitespace are excluded.
18    pub indent: usize,
19}
20
21impl CodeFence {
22    pub(crate) fn frontmatter_open(bytes: &[u8]) -> Option<Self> {
23        let marker = *bytes.first()?;
24        if !matches!(marker, b'-' | b'+' | b'`' | b'~') {
25            return None;
26        }
27        let length = bytes.iter().take_while(|&&byte| byte == marker).count();
28        if length < 3 || (matches!(marker, b'-' | b'+') && length != 3) {
29            return None;
30        }
31        Some(Self {
32            character: char::from(marker),
33            length,
34            indent: 0,
35        })
36    }
37
38    pub(crate) fn valid_frontmatter_info(self, info: &[u8]) -> bool {
39        !info.iter().any(|byte| matches!(byte, b'\r' | b'\n'))
40            && (!matches!(self.character, '`' | '~')
41                || !info.iter().all(|byte| matches!(byte, b' ' | b'\t')))
42            && (self.character != '`' || !info.contains(&b'`'))
43    }
44
45    // The caller strips only the indentation permitted in its source context.
46    pub(crate) fn frontmatter_close(self, line: &[u8]) -> Option<usize> {
47        let count = line
48            .iter()
49            .take_while(|&&byte| char::from(byte) == self.character)
50            .count();
51        (count >= self.length
52            && (!matches!(self.character, '-' | '+') || count == self.length)
53            && line[count..]
54                .iter()
55                .all(|byte| matches!(byte, b' ' | b'\t')))
56        .then_some(count)
57    }
58}
base_markdown/code_fence.rs

base_markdown/
code_fence.rs
