//! This file implements the rendering logic of cheddar with public //! functions for syntax-highlighting code and for turning Markdown //! into HTML with TVL extensions. 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 regex::Regex; 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::{Theme, ThemeSet}; use syntect::parsing::{SyntaxReference, SyntaxSet}; use syntect::util::LinesWithEndings; use syntect::html::{ append_highlighted_html_for_styled_line, start_highlighted_html_snippet, IncludeBackground, }; #[cfg(test)] mod tests; lazy_static! { // Load syntaxes lazily. Initialisation might not be required in // the case of Markdown rendering (if there's no code blocks // within the document). // // Note that the syntax set is included from the path pointed to // by the BAT_SYNTAXES environment variable at compile time. This // variable is populated by Nix and points to TVL's syntax set. static ref SYNTAXES: SyntaxSet = from_binary(include_bytes!(env!("BAT_SYNTAXES"))); pub static ref THEMES: ThemeSet = ThemeSet::load_defaults(); // Configure Comrak's Markdown rendering with all the bells & // whistles! static ref MD_OPTS: ComrakOptions = { let mut options = ComrakOptions::default(); // Enable non-standard Markdown features: options.extension.strikethrough = true; options.extension.tagfilter = true; options.extension.table = true; options.extension.autolink = true; options.extension.tasklist = true; options.extension.header_ids = Some(String::new()); // yyeeesss! options.extension.footnotes = true; options.extension.description_lists = true; options.extension.front_matter_delimiter = Some("---".to_owned()); // Required for tagfilter options.render.unsafe_ = true; options }; // 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 }; // Default shortlink set used in cheddar (i.e. TVL's shortlinks) static ref TVL_LINKS: Vec = vec![ // TVL shortlinks for bugs and changelists (e.g. b/123, // cl/123). Coincidentally these have the same format, which // makes the initial implementation easy. Shortlink { pattern: Regex::new(r#"\b(?Pb|cl)/(?P\d+)\b"#).unwrap(), replacement: "[$type/$dest](https://$type.tvl.fyi/$dest)", } ]; } /// Structure that describes a single shortlink that should be /// automatically highlighted. Highlighting is performed as a string /// replacement over input Markdown. pub struct Shortlink { /// Short link pattern to recognise. Make sure to anchor these /// correctly. pub pattern: Regex, /// Replacement string, as per the documentation of /// [`Regex::replace`]. pub replacement: &'static str, } // HTML fragment used when rendering inline blocks in Markdown documents. // Emulates the GitHub style (subtle background hue and padding). const BLOCK_PRE: &str = "
\n";

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 mut block = NodeHtmlBlock::default(); block.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(b"TODO") { return Some(Callout::Todo); } else if text.starts_with(b"WARNING") { return Some(Callout::Warning); } else if text.starts_with(b"QUESTION") { return Some(Callout::Question); } else if text.starts_with(b"TIP") { return Some(Callout::Tip); } None } _ => None, }, _ => None, } } // Replace instances of known shortlinks in the input document with // Markdown syntax for a highlighted link. fn linkify_shortlinks(mut text: String, shortlinks: &[Shortlink]) -> String { for link in shortlinks { text = link .pattern .replace_all(&text, link.replacement) .to_string(); } return text; } 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", }; let mut block = NodeHtmlBlock::default(); block.literal = format!("

", class).into_bytes(); NodeValue::HtmlBlock(block) } pub fn format_markdown_with_shortlinks( reader: &mut R, writer: &mut W, shortlinks: &[Shortlink], ) { let document = { let mut buffer = String::new(); reader .read_to_string(&mut buffer) .expect("reading should work"); buffer }; let arena = Arena::new(); let root = parse_document(&arena, &linkify_shortlinks(document, shortlinks), &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 mut p_close_value = NodeHtmlBlock::default(); p_close_value.literal = b"

".to_vec(); let p_close_node = Ast::new(NodeValue::HtmlBlock(p_close_value)); let p_close = Node::new(RefCell::new(p_close_node)); // Special features of Cheddar are implemented by traversing the // arena and reacting on nodes that we might want to modify. iter_nodes(root, &|node| { let mut ast = node.data.borrow_mut(); let new = match &ast.value { // Syntax highlighting is implemented by replacing the // code block node with literal HTML. 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"); } pub fn format_markdown(reader: &mut R, writer: &mut W) { format_markdown_with_shortlinks(reader, writer, &TVL_LINKS) } fn find_syntax_for_file(filename: &str) -> &'static SyntaxReference { (*FILENAME_OVERRIDES) .get(filename) .and_then(|name| SYNTAXES.find_syntax_by_name(name)) .or_else(|| { Path::new(filename) .extension() .and_then(OsStr::to_str) .and_then(|s| SYNTAXES.find_syntax_by_extension(s)) }) .unwrap_or_else(|| SYNTAXES.find_syntax_plain_text()) } pub fn format_code( theme: &Theme, reader: &mut R, writer: &mut W, filename: &str, ) { 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); let syntax = find_syntax_for_file(filename); 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"); }