Function parse_lang_reference

std/src/help.rs:271–305

Parses the `lang.md` file and extracts a mapping of language reference topics to their descriptions. Note that, even if the input looks like Markdown, we do *not* implement a Markdown parser here. The structure of the file is strict and well-known in advance, so this will panic if there are problems in the input data.

(lang_md: &'static str)

/// The structure of the file is strict and well-known in advance, so this will panic if there are
/// problems in the input data.
fn parse_lang_reference(lang_md: &'static str) -> Vec<(&'static str, &'static str)> {
    let mut topics = vec![];

    // Cope with Windows checkouts.  It's tempting to make this a build-time conditional on the OS
    // name, but we don't know how the files are checked out.  Assume CRLF delimiters if we see at
    // least one of them.
    let line_end;
    let section_start;
    let body_start;
    if lang_md.contains("\r\n") {
        line_end = "\r\n";
        section_start = "\r\n\r\n# ";
        body_start = "\r\n\r\n";
    } else {
        line_end = "\n";
        section_start = "\n\n# ";
        body_start = "\n\n";
    }

    for (start, _match) in lang_md.match_indices(section_start) {
        let section = &lang_md[start + section_start.len()..];

        let title_end = section.find(body_start).expect("Hardcoded text must be valid");
        let title = &section[..title_end];
        let section = &section[title_end + body_start.len()..];

        let end = section.find(section_start).unwrap_or_else(|| {
            if section.ends_with(line_end) { section.len() - line_end.len() } else { section.len() }
        });
        let content = &section[..end];
        topics.push((title, content));
    }

    topics
}

/// Maintains the collection of topics as a trie indexed by their name.
struct Topics(Trie<String, Box<dyn Topic>>);