A bare minimum pulldown_cmark highlighting using syntect based off of conversation in: https://github.com/raphlinus/pulldown-cmark/issues/167

markdown_highlight.rs

use syntect::highlighting::ThemeSet;
use syntect::html::highlighted_html_for_string;
use syntect::parsing::SyntaxSet;

use pulldown_cmark::{html, CodeBlockKind, CowStr, Event, Options, Parser, Tag};

fn main() {
    // Setup for pulldown_cmark to read (only) from stdin
    let opts = Options::all();
    let input = String::from(
        r#"Test

```bash
sh install.sh && echo "true"
```

Test"#,
    );
    let mut s = String::with_capacity(&input.len() * 3 / 2);
    let p = Parser::new_ext(&input, opts);

    // Setup for syntect to highlight (specifically) Rust code
    let ss = SyntaxSet::load_defaults_newlines();
    let ts = ThemeSet::load_defaults();
    let theme = &ts.themes["Solarized (light)"];
    // We'll build a new vector of events since we can only consume the parser once
    let mut new_p = Vec::new();
    // As we go along, we'll want to highlight code in bundles, not lines
    let mut to_highlight = String::new();
    // And track a little bit of state
    let mut in_code_block = false;

    p.for_each(|event| match event {
        Event::Start(Tag::CodeBlock(_)) => {
            in_code_block = true;
        }
        Event::End(Tag::CodeBlock(ref token)) => {
            if in_code_block {
                let syntax = if let CodeBlockKind::Fenced(val) = token {
                    ss.find_syntax_by_extension(&val.clone().into_string())
                        .unwrap_or_else(|| ss.find_syntax_plain_text())
                } else {
                    ss.find_syntax_plain_text()
                };
                // Format the whole multi-line code block as HTML all at once
                let html = highlighted_html_for_string(&to_highlight, &ss, &syntax, &theme);
                // And put it into the vector
                new_p.push(Event::Html(CowStr::Boxed(html.into_boxed_str())));
                to_highlight = String::new();
                in_code_block = false;
            }
        }
        Event::Text(t) => {
            if in_code_block {
                // If we're in a code block, build up the string of text
                to_highlight.push_str(&t);
            } else {
                new_p.push(Event::Text(t))
            }
        }
        e => {
            new_p.push(e);
        }
    });

    // Now we send this new vector of events off to be transformed into HTML
    html::push_html(&mut s, new_p.into_iter());
    print!("{}", s);
}