1 files changed, 198 insertions, 0 deletions
diff --git a/tools/cheddar/src/main.rs b/tools/cheddar/src/main.rs
new file mode 100644
index 000000000000..d0115d391c9d
--- /dev/null
+++ b/tools/cheddar/src/main.rs
@@ -0,0 +1,198 @@
+use comrak::nodes::{AstNode, NodeValue, NodeHtmlBlock};
+use comrak::{Arena, parse_document, format_html, ComrakOptions};
+use lazy_static::lazy_static;
+use std::env;
+use std::ffi::OsStr;
+use std::io::BufRead;
+use std::io::Read;
+use std::io;
+use std::path::Path;
+use syntect::dumps::from_binary;
+use syntect::easy::HighlightLines;
+use syntect::highlighting::ThemeSet;
+use syntect::parsing::{SyntaxSet, SyntaxReference};
+use syntect::util::LinesWithEndings;
+
+use syntect::html::{
+    IncludeBackground,
+    append_highlighted_html_for_styled_line,
+    start_highlighted_html_snippet,
+};
+
+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()
+    };
+}
+
+// HTML fragment used when rendering inline blocks in Markdown documents.
+// Emulates the GitHub style (subtle background hue and padding).
+const BLOCK_PRE: &str = "<pre style=\"background-color:#f6f8fa;padding:16px;\">\n";
+
+fn args_extension() -> Option<String> {
+    // The name of the file to be formatted is usually passed in as
+    // the first argument and can be used to determine a syntax set.
+    let args = env::args().collect::<Vec<String>>();
+    if args.len() != 2 {
+        return None
+    }
+
+    Path::new(&args[1]).extension()
+        .and_then(OsStr::to_str)
+        .map(|s| s.to_string())
+}
+
+fn should_continue(res: &io::Result<usize>) -> 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> {
+    SYNTAXES.syntaxes().iter().rev().find(|&s| info.eq_ignore_ascii_case(&s.name))
+}
+
+fn format_markdown() {
+    let document = {
+        let mut buffer = String::new();
+        let stdin = io::stdin();
+        let mut stdin = stdin.lock();
+        stdin.read_to_string(&mut buffer).expect("failed to read stdin");
+        buffer
+    };
+
+    let arena = Arena::new();
+    let root = parse_document(&arena, &document, &MD_OPTS);
+
+    // 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();
+        match &ast.value {
+            NodeValue::CodeBlock(code_block) => {
+                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(
+                            &regions[..], IncludeBackground::No, &mut buf,
+                        );
+                    }
+
+                    buf.push_str("</pre>");
+                    buf
+                };
+
+                let block = NodeHtmlBlock {
+                    block_type: 1, // It's unclear what behaviour is toggled by this
+                    literal: rendered.into_bytes(),
+                };
+
+                ast.value = NodeValue::HtmlBlock(block);
+            },
+            _ => (),
+        };
+    });
+
+    format_html(root, &MD_OPTS, &mut io::stdout())
+        .expect("Markdown rendering failed");
+}
+
+fn format_code(extension: Option<&str>) {
+    let stdin = io::stdin();
+    let mut stdin = stdin.lock();
+    let mut linebuf = String::new();
+
+    // Get the first line, we might need it for syntax identification.
+    let mut read_result = stdin.read_line(&mut linebuf);
+
+    // Set up the highlighter
+    let theme = &THEMES.themes["InspiredGitHub"];
+
+    let syntax = extension
+        .and_then(|e| SYNTAXES.find_syntax_by_extension(e))
+        .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(
+            &regions[..],
+            IncludeBackground::IfDifferent(bg),
+            &mut outbuf,
+        );
+
+        // immediately output the current state to avoid keeping
+        // things in memory
+        print!("{}", outbuf);
+
+        // merry go round again
+        linebuf.clear();
+        outbuf.clear();
+        read_result = stdin.read_line(&mut linebuf);
+    }
+
+    println!("</pre>");
+}
+
+fn main() {
+    let extension = args_extension();
+    match extension.as_ref().map(String::as_str) {
+        Some("md") => format_markdown(),
+        extension => format_code(extension),
+    }
+}