use clap::{App, Arg}; use comrak::arena_tree::Node; use comrak::nodes::{Ast, AstNode, NodeCodeBlock, NodeHtmlBlock, NodeValue}; use comrak::{format_html, parse_document, Arena, ComrakOptions}; use lazy_static::lazy_static; use std::cell::RefCell; use std::collections::HashMap; use std::env; use std::ffi::OsStr; use std::io; use std::io::BufRead; use std::io::Write; use std::path::Path; use syntect::dumps::from_binary; use syntect::easy::HighlightLines; use syntect::highlighting::ThemeSet; use syntect::parsing::{SyntaxReference, SyntaxSet}; use syntect::util::LinesWithEndings; use syntect::html::{ append_highlighted_html_for_styled_line, start_highlighted_html_snippet, IncludeBackground, }; lazy_static! { // Load syntaxes & themes lazily. Initialisation might not be // required in the case of Markdown rendering (if there's no code // blocks within the document). static ref SYNTAXES: SyntaxSet = from_binary(include_bytes!(env!("BAT_SYNTAXES"))); static ref THEMES: ThemeSet = ThemeSet::load_defaults(); // Configure Comrak's Markdown rendering with all the bells & // whistles! static ref MD_OPTS: ComrakOptions = ComrakOptions{ ext_strikethrough: true, ext_tagfilter: true, ext_table: true, ext_autolink: true, ext_tasklist: true, ext_header_ids: Some(String::new()), // yyeeesss! ext_footnotes: true, ext_description_lists: true, unsafe_: true, // required for tagfilter ..ComrakOptions::default() }; // Configures a map of specific filenames to languages, for cases // where the detection by extension or other heuristics fails. static ref FILENAME_OVERRIDES: HashMap<&'static str, &'static str> = { let mut map = HashMap::new(); // rules.pl is the canonical name of the submit rule file in // Gerrit, which is written in Prolog. map.insert("rules.pl", "Prolog"); map }; } // HTML fragment used when rendering inline blocks in Markdown documents. // Emulates the GitHub style (subtle background hue and padding). const BLOCK_PRE: &str = "
\n";

#[derive(Debug, Default)]
struct Args {
    /// Should Cheddar run as an about filter? (i.e. give special
    /// rendering treatment to Markdown documents)
    about_filter: bool,

    /// What file extension has been supplied (if any)?
    extension: Option,

    /// Which language to override the detection to (if any)?
    lang_override: Option<&'static str>,
}

fn should_continue(res: &io::Result) -> bool {
    match *res {
        Ok(n) => n > 0,
        Err(_) => false,
    }
}

// This function is taken from the Comrak documentation.
fn iter_nodes<'a, F>(node: &'a AstNode<'a>, f: &F)
where
    F: Fn(&'a AstNode<'a>),
{
    f(node);
    for c in node.children() {
        iter_nodes(c, f);
    }
}

// Many of the syntaxes in the syntax list have random capitalisations, which
// means that name matching for the block info of a code block in HTML fails.
//
// Instead, try finding a syntax match by comparing case insensitively (for
// ASCII characters, anyways).
fn find_syntax_case_insensitive(info: &str) -> Option<&'static SyntaxReference> {
    // TODO(tazjin): memoize this lookup
    SYNTAXES
        .syntaxes()
        .iter()
        .rev()
        .find(|&s| info.eq_ignore_ascii_case(&s.name))
}

// Replaces code-block inside of a Markdown AST with HTML blocks rendered by
// syntect. This enables static (i.e. no JavaScript) syntax highlighting, even
// of complex languages.
fn highlight_code_block(code_block: &NodeCodeBlock) -> NodeValue {
    let theme = &THEMES.themes["InspiredGitHub"];
    let info = String::from_utf8_lossy(&code_block.info);

    let syntax = find_syntax_case_insensitive(&info)
        .or_else(|| SYNTAXES.find_syntax_by_extension(&info))
        .unwrap_or_else(|| SYNTAXES.find_syntax_plain_text());

    let code = String::from_utf8_lossy(&code_block.literal);

    let rendered = {
        // Write the block preamble manually to get exactly the
        // desired layout:
        let mut hl = HighlightLines::new(syntax, theme);
        let mut buf = BLOCK_PRE.to_string();

        for line in LinesWithEndings::from(&code) {
            let regions = hl.highlight(line, &SYNTAXES);
            append_highlighted_html_for_styled_line(®ions[..], IncludeBackground::No, &mut buf);
        }

        buf.push_str("
"); buf }; let block = NodeHtmlBlock { block_type: 1, // It's unclear what behaviour is toggled by this literal: rendered.into_bytes(), }; NodeValue::HtmlBlock(block) } // Supported callout elements (which each have their own distinct rendering): enum Callout { Todo, Warning, Question, Tip, } // Determine whether the first child of the supplied node contains a text that // should cause a callout section to be rendered. fn has_callout<'a>(node: &Node<'a, RefCell>) -> Option { match node.first_child().map(|c| c.data.borrow()) { Some(child) => match &child.value { NodeValue::Text(text) => { if text.starts_with("TODO".as_bytes()) { return Some(Callout::Todo); } else if text.starts_with("WARNING".as_bytes()) { return Some(Callout::Warning); } else if text.starts_with("QUESTION".as_bytes()) { return Some(Callout::Question); } else if text.starts_with("TIP".as_bytes()) { return Some(Callout::Tip); } return None; } _ => return None, }, _ => return None, } } fn format_callout_paragraph(callout: Callout) -> NodeValue { let class = match callout { Callout::Todo => "cheddar-todo", Callout::Warning => "cheddar-warning", Callout::Question => "cheddar-question", Callout::Tip => "cheddar-tip", }; NodeValue::HtmlBlock(NodeHtmlBlock { block_type: 1, literal: format!("

", class).into_bytes(), }) } fn format_markdown(reader: &mut R, writer: &mut W) { let document = { let mut buffer = String::new(); reader .read_to_string(&mut buffer) .expect("reading should work"); drop(reader); buffer }; let arena = Arena::new(); let root = parse_document(&arena, &document, &MD_OPTS); // This node must exist with a lifetime greater than that of the parsed AST // in case that callouts are encountered (otherwise insertion into the tree // is not possible). let p_close = Node::new(RefCell::new(Ast { start_line: 0, // TODO(tazjin): hrmm content: vec![], open: false, last_line_blank: false, value: NodeValue::HtmlBlock(NodeHtmlBlock { block_type: 1, literal: "

".as_bytes().to_vec(), }), })); // Syntax highlighting is implemented by traversing the arena and // replacing all code blocks with HTML blocks rendered by syntect. iter_nodes(root, &|node| { let mut ast = node.data.borrow_mut(); let new = match &ast.value { NodeValue::CodeBlock(code) => Some(highlight_code_block(code)), NodeValue::Paragraph => { if let Some(callout) = has_callout(node) { node.insert_after(&p_close); Some(format_callout_paragraph(callout)) } else { None } } _ => None, }; if let Some(new_value) = new { ast.value = new_value } }); format_html(root, &MD_OPTS, writer).expect("Markdown rendering failed"); } fn format_code(reader: &mut R, writer: &mut W, args: &Args) { let mut linebuf = String::new(); // Get the first line, we might need it for syntax identification. let mut read_result = reader.read_line(&mut linebuf); // Set up the highlighter let theme = &THEMES.themes["InspiredGitHub"]; let syntax = args .lang_override .and_then(|l| SYNTAXES.find_syntax_by_name(l)) .or_else(|| match args.extension { Some(ref ext) => SYNTAXES.find_syntax_by_extension(ext), None => None, }) .or_else(|| SYNTAXES.find_syntax_by_first_line(&linebuf)) .unwrap_or_else(|| SYNTAXES.find_syntax_plain_text()); let mut hl = HighlightLines::new(syntax, theme); let (mut outbuf, bg) = start_highlighted_html_snippet(theme); // Rather than using the `lines` iterator, read each line manually // and maintain buffer state. // // This is done because the syntax highlighter requires trailing // newlines to be efficient, and those are stripped in the lines // iterator. while should_continue(&read_result) { let regions = hl.highlight(&linebuf, &SYNTAXES); append_highlighted_html_for_styled_line( ®ions[..], IncludeBackground::IfDifferent(bg), &mut outbuf, ); // immediately output the current state to avoid keeping // things in memory write!(writer, "{}", outbuf).expect("write should not fail"); // merry go round again linebuf.clear(); outbuf.clear(); read_result = reader.read_line(&mut linebuf); } writeln!(writer, "").expect("write should not fail"); } fn main() { // Parse the command-line flags passed to cheddar to determine // whether it is running in about-filter mode (`--about-filter`) // and what file extension has been supplied. let matches = App::new("cheddar") .about("TVL's syntax highlighter") .arg( Arg::with_name("about-filter") .help("Run as a cgit about-filter (renders Markdown)") .long("about-filter") .takes_value(false), ) .arg(Arg::with_name("filename").help("File to render").index(1)) .get_matches(); let mut args = Args::default(); args.about_filter = matches.is_present("about-filter"); let filename = matches.value_of("filename").expect("filename is required"); if let Some(lang) = (*FILENAME_OVERRIDES).get(filename) { args.lang_override = Some(lang); } args.extension = Path::new(&filename) .extension() .and_then(OsStr::to_str) .map(|s| s.to_string()); let stdin = io::stdin(); let mut in_handle = stdin.lock(); let stdout = io::stdout(); let mut out_handle = stdout.lock(); match args.extension.as_ref().map(String::as_str) { Some("md") if args.about_filter => format_markdown(&mut in_handle, &mut out_handle), _ => format_code(&mut in_handle, &mut out_handle, &args), } }