rust/src/librustdoc/html/markdown.rs

// Copyright 2013-2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! Markdown formatting for rustdoc
//!
//! This module implements markdown formatting through the pulldown-cmark
//! rust-library. This module exposes all of the
//! functionality through a unit-struct, `Markdown`, which has an implementation
//! of `fmt::Display`. Example usage:
//!
//! ```
//! use rustdoc::html::markdown::Markdown;
//!
//! let s = "My *markdown* _text_";
//! let html = format!("{}", Markdown(s));
//! // ... something using html
//! ```

#![allow(non_camel_case_types)]

use libc;
use std::slice;

use std::ascii::AsciiExt;
use std::cell::RefCell;
use std::collections::{HashMap, VecDeque};
use std::default::Default;
use std::fmt::{self, Write};
use std::str;
use syntax::feature_gate::UnstableFeatures;
use syntax::codemap::Span;

use html::render::derive_id;
use html::toc::TocBuilder;
use html::highlight;
use html::escape::Escape;
use test;

use pulldown_cmark::{html, Event, Tag, Parser};
use pulldown_cmark::{Options, OPTION_ENABLE_FOOTNOTES, OPTION_ENABLE_TABLES};

#[derive(PartialEq, Debug, Clone, Copy)]
pub enum RenderType {
    Hoedown,
    Pulldown,
}

/// A unit struct which has the `fmt::Display` trait implemented. When
/// formatted, this struct will emit the HTML corresponding to the rendered
/// version of the contained markdown string.
// The second parameter is whether we need a shorter version or not.
pub struct Markdown<'a>(pub &'a str, pub RenderType);
/// A unit struct like `Markdown`, that renders the markdown with a
/// table of contents.
pub struct MarkdownWithToc<'a>(pub &'a str, pub RenderType);
/// A unit struct like `Markdown`, that renders the markdown escaping HTML tags.
pub struct MarkdownHtml<'a>(pub &'a str, pub RenderType);
/// A unit struct like `Markdown`, that renders only the first paragraph.
pub struct MarkdownSummaryLine<'a>(pub &'a str);

/// Controls whether a line will be hidden or shown in HTML output.
///
/// All lines are used in documentation tests.
enum Line<'a> {
    Hidden(&'a str),
    Shown(&'a str),
}

impl<'a> Line<'a> {
    fn for_html(self) -> Option<&'a str> {
        match self {
            Line::Shown(l) => Some(l),
            Line::Hidden(_) => None,
        }
    }

    fn for_code(self) -> &'a str {
        match self {
            Line::Shown(l) |
            Line::Hidden(l) => l,
        }
    }
}

// FIXME: There is a minor inconsistency here. For lines that start with ##, we
// have no easy way of removing a potential single space after the hashes, which
// is done in the single # case. This inconsistency seems okay, if non-ideal. In
// order to fix it we'd have to iterate to find the first non-# character, and
// then reallocate to remove it; which would make us return a String.
fn map_line(s: &str) -> Line {
    let trimmed = s.trim();
    if trimmed.starts_with("##") {
        Line::Shown(&trimmed[1..])
    } else if trimmed.starts_with("# ") {
        // # text
        Line::Hidden(&trimmed[2..])
    } else if trimmed == "#" {
        // We cannot handle '#text' because it could be #[attr].
        Line::Hidden("")
    } else {
        Line::Shown(s)
    }
}

/// Returns a new string with all consecutive whitespace collapsed into
/// single spaces.
///
/// Any leading or trailing whitespace will be trimmed.
fn collapse_whitespace(s: &str) -> String {
    s.split_whitespace().collect::<Vec<_>>().join(" ")
}

/// Convert chars from a title for an id.
///
/// "Hello, world!" -> "hello-world"
fn slugify(c: char) -> Option<char> {
    if c.is_alphanumeric() || c == '-' || c == '_' {
        if c.is_ascii() {
            Some(c.to_ascii_lowercase())
        } else {
            Some(c)
        }
    } else if c.is_whitespace() && c.is_ascii() {
        Some('-')
    } else {
        None
    }
}

// Information about the playground if a URL has been specified, containing an
// optional crate name and the URL.
thread_local!(pub static PLAYGROUND: RefCell<Option<(Option<String>, String)>> = {
    RefCell::new(None)
});

/// Adds syntax highlighting and playground Run buttons to rust code blocks.
struct CodeBlocks<'a, I: Iterator<Item = Event<'a>>> {
    inner: I,
}

impl<'a, I: Iterator<Item = Event<'a>>> CodeBlocks<'a, I> {
    fn new(iter: I) -> Self {
        CodeBlocks {
            inner: iter,
        }
    }
}

impl<'a, I: Iterator<Item = Event<'a>>> Iterator for CodeBlocks<'a, I> {
    type Item = Event<'a>;

    fn next(&mut self) -> Option<Self::Item> {
        let event = self.inner.next();
        if let Some(Event::Start(Tag::CodeBlock(lang))) = event {
            if !LangString::parse(&lang).rust {
                return Some(Event::Start(Tag::CodeBlock(lang)));
            }
        } else {
            return event;
        }

        let mut origtext = String::new();
        for event in &mut self.inner {
            match event {
                Event::End(Tag::CodeBlock(..)) => break,
                Event::Text(ref s) => {
                    origtext.push_str(s);
                }
                _ => {}
            }
        }
        let lines = origtext.lines().filter_map(|l| map_line(l).for_html());
        let text = lines.collect::<Vec<&str>>().join("\n");
        PLAYGROUND.with(|play| {
            // insert newline to clearly separate it from the
            // previous block so we can shorten the html output
            let mut s = String::from("\n");
            let playground_button = play.borrow().as_ref().and_then(|&(ref krate, ref url)| {
                if url.is_empty() {
                    return None;
                }
                let test = origtext.lines()
                    .map(|l| map_line(l).for_code())
                    .collect::<Vec<&str>>().join("\n");
                let krate = krate.as_ref().map(|s| &**s);
                let test = test::maketest(&test, krate, false,
                                        &Default::default());
                let channel = if test.contains("#![feature(") {
                    "&amp;version=nightly"
                } else {
                    ""
                };
                // These characters don't need to be escaped in a URI.
                // FIXME: use a library function for percent encoding.
                fn dont_escape(c: u8) -> bool {
                    (b'a' <= c && c <= b'z') ||
                    (b'A' <= c && c <= b'Z') ||
                    (b'0' <= c && c <= b'9') ||
                    c == b'-' || c == b'_' || c == b'.' ||
                    c == b'~' || c == b'!' || c == b'\'' ||
                    c == b'(' || c == b')' || c == b'*'
                }
                let mut test_escaped = String::new();
                for b in test.bytes() {
                    if dont_escape(b) {
                        test_escaped.push(char::from(b));
                    } else {
                        write!(test_escaped, "%{:02X}", b).unwrap();
                    }
                }
                Some(format!(
                    r#"<a class="test-arrow" target="_blank" href="{}?code={}{}">Run</a>"#,
                    url, test_escaped, channel
                ))
            });
            s.push_str(&highlight::render_with_highlighting(
                        &text,
                        Some("rust-example-rendered"),
                        None,
                        playground_button.as_ref().map(String::as_str)));
            Some(Event::Html(s.into()))
        })
    }
}

/// Make headings links with anchor ids and build up TOC.
struct HeadingLinks<'a, 'b, I: Iterator<Item = Event<'a>>> {
    inner: I,
    toc: Option<&'b mut TocBuilder>,
    buf: VecDeque<Event<'a>>,
}

impl<'a, 'b, I: Iterator<Item = Event<'a>>> HeadingLinks<'a, 'b, I> {
    fn new(iter: I, toc: Option<&'b mut TocBuilder>) -> Self {
        HeadingLinks {
            inner: iter,
            toc: toc,
            buf: VecDeque::new(),
        }
    }
}

impl<'a, 'b, I: Iterator<Item = Event<'a>>> Iterator for HeadingLinks<'a, 'b, I> {
    type Item = Event<'a>;

    fn next(&mut self) -> Option<Self::Item> {
        if let Some(e) = self.buf.pop_front() {
            return Some(e);
        }

        let event = self.inner.next();
        if let Some(Event::Start(Tag::Header(level))) = event {
            let mut id = String::new();
            for event in &mut self.inner {
                match event {
                    Event::End(Tag::Header(..)) => break,
                    Event::Text(ref text) => id.extend(text.chars().filter_map(slugify)),
                    _ => {},
                }
                self.buf.push_back(event);
            }
            let id = derive_id(id);

            if let Some(ref mut builder) = self.toc {
                let mut html_header = String::new();
                html::push_html(&mut html_header, self.buf.iter().cloned());
                let sec = builder.push(level as u32, html_header, id.clone());
                self.buf.push_front(Event::InlineHtml(format!("{} ", sec).into()));
            }

            self.buf.push_back(Event::InlineHtml(format!("</a></h{}>", level).into()));

            let start_tags = format!("<h{level} id=\"{id}\" class=\"section-header\">\
                                      <a href=\"#{id}\">",
                                     id = id,
                                     level = level);
            return Some(Event::InlineHtml(start_tags.into()));
        }
        event
    }
}

/// Extracts just the first paragraph.
struct SummaryLine<'a, I: Iterator<Item = Event<'a>>> {
    inner: I,
    started: bool,
    depth: u32,
}

impl<'a, I: Iterator<Item = Event<'a>>> SummaryLine<'a, I> {
    fn new(iter: I) -> Self {
        SummaryLine {
            inner: iter,
            started: false,
            depth: 0,
        }
    }
}

impl<'a, I: Iterator<Item = Event<'a>>> Iterator for SummaryLine<'a, I> {
    type Item = Event<'a>;

    fn next(&mut self) -> Option<Self::Item> {
        if self.started && self.depth == 0 {
            return None;
        }
        if !self.started {
            self.started = true;
        }
        let event = self.inner.next();
        match event {
            Some(Event::Start(..)) => self.depth += 1,
            Some(Event::End(..)) => self.depth -= 1,
            _ => {}
        }
        event
    }
}

/// Moves all footnote definitions to the end and add back links to the
/// references.
struct Footnotes<'a, I: Iterator<Item = Event<'a>>> {
    inner: I,
    footnotes: HashMap<String, (Vec<Event<'a>>, u16)>,
}

impl<'a, I: Iterator<Item = Event<'a>>> Footnotes<'a, I> {
    fn new(iter: I) -> Self {
        Footnotes {
            inner: iter,
            footnotes: HashMap::new(),
        }
    }
    fn get_entry(&mut self, key: &str) -> &mut (Vec<Event<'a>>, u16) {
        let new_id = self.footnotes.keys().count() + 1;
        let key = key.to_owned();
        self.footnotes.entry(key).or_insert((Vec::new(), new_id as u16))
    }
}

impl<'a, I: Iterator<Item = Event<'a>>> Iterator for Footnotes<'a, I> {
    type Item = Event<'a>;

    fn next(&mut self) -> Option<Self::Item> {
        loop {
            match self.inner.next() {
                Some(Event::FootnoteReference(ref reference)) => {
                    let entry = self.get_entry(&reference);
                    let reference = format!("<sup id=\"supref{0}\"><a href=\"#ref{0}\">{0}\
                                             </a></sup>",
                                            (*entry).1);
                    return Some(Event::Html(reference.into()));
                }
                Some(Event::Start(Tag::FootnoteDefinition(def))) => {
                    let mut content = Vec::new();
                    for event in &mut self.inner {
                        if let Event::End(Tag::FootnoteDefinition(..)) = event {
                            break;
                        }
                        content.push(event);
                    }
                    let entry = self.get_entry(&def);
                    (*entry).0 = content;
                }
                Some(e) => return Some(e),
                None => {
                    if !self.footnotes.is_empty() {
                        let mut v: Vec<_> = self.footnotes.drain().map(|(_, x)| x).collect();
                        v.sort_by(|a, b| a.1.cmp(&b.1));
                        let mut ret = String::from("<div class=\"footnotes\"><hr><ol>");
                        for (mut content, id) in v {
                            write!(ret, "<li id=\"ref{}\">", id).unwrap();
                            let mut is_paragraph = false;
                            if let Some(&Event::End(Tag::Paragraph)) = content.last() {
                                content.pop();
                                is_paragraph = true;
                            }
                            html::push_html(&mut ret, content.into_iter());
                            write!(ret,
                                   "&nbsp;<a href=\"#supref{}\" rev=\"footnote\">↩</a>",
                                   id).unwrap();
                            if is_paragraph {
                                ret.push_str("</p>");
                            }
                            ret.push_str("</li>");
                        }
                        ret.push_str("</ol></div>");
                        return Some(Event::Html(ret.into()));
                    } else {
                        return None;
                    }
                }
            }
        }
    }
}

const DEF_OUNIT: libc::size_t = 64;
const HOEDOWN_EXT_NO_INTRA_EMPHASIS: libc::c_uint = 1 << 11;
const HOEDOWN_EXT_TABLES: libc::c_uint = 1 << 0;
const HOEDOWN_EXT_FENCED_CODE: libc::c_uint = 1 << 1;
const HOEDOWN_EXT_AUTOLINK: libc::c_uint = 1 << 3;
const HOEDOWN_EXT_STRIKETHROUGH: libc::c_uint = 1 << 4;
const HOEDOWN_EXT_SUPERSCRIPT: libc::c_uint = 1 << 8;
const HOEDOWN_EXT_FOOTNOTES: libc::c_uint = 1 << 2;
const HOEDOWN_HTML_ESCAPE: libc::c_uint = 1 << 1;

const HOEDOWN_EXTENSIONS: libc::c_uint =
    HOEDOWN_EXT_NO_INTRA_EMPHASIS | HOEDOWN_EXT_TABLES |
    HOEDOWN_EXT_FENCED_CODE | HOEDOWN_EXT_AUTOLINK |
    HOEDOWN_EXT_STRIKETHROUGH | HOEDOWN_EXT_SUPERSCRIPT |
    HOEDOWN_EXT_FOOTNOTES;

enum hoedown_document {}

type blockcodefn = extern "C" fn(*mut hoedown_buffer, *const hoedown_buffer,
                                 *const hoedown_buffer, *const hoedown_renderer_data,
                                 libc::size_t);

type blockquotefn = extern "C" fn(*mut hoedown_buffer, *const hoedown_buffer,
                                  *const hoedown_renderer_data, libc::size_t);

type headerfn = extern "C" fn(*mut hoedown_buffer, *const hoedown_buffer,
                              libc::c_int, *const hoedown_renderer_data,
                              libc::size_t);

type blockhtmlfn = extern "C" fn(*mut hoedown_buffer, *const hoedown_buffer,
                                 *const hoedown_renderer_data, libc::size_t);

type codespanfn = extern "C" fn(*mut hoedown_buffer, *const hoedown_buffer,
                                *const hoedown_renderer_data, libc::size_t) -> libc::c_int;

type linkfn = extern "C" fn (*mut hoedown_buffer, *const hoedown_buffer,
                             *const hoedown_buffer, *const hoedown_buffer,
                             *const hoedown_renderer_data, libc::size_t) -> libc::c_int;

type entityfn = extern "C" fn (*mut hoedown_buffer, *const hoedown_buffer,
                               *const hoedown_renderer_data, libc::size_t);

type normaltextfn = extern "C" fn(*mut hoedown_buffer, *const hoedown_buffer,
                                  *const hoedown_renderer_data, libc::size_t);

#[repr(C)]
struct hoedown_renderer_data {
    opaque: *mut libc::c_void,
}

#[repr(C)]
struct hoedown_renderer {
    opaque: *mut libc::c_void,

    blockcode: Option<blockcodefn>,
    blockquote: Option<blockquotefn>,
    header: Option<headerfn>,

    other_block_level_callbacks: [libc::size_t; 11],

    blockhtml: Option<blockhtmlfn>,

    /* span level callbacks - NULL or return 0 prints the span verbatim */
    autolink: libc::size_t, // unused
    codespan: Option<codespanfn>,
    other_span_level_callbacks_1: [libc::size_t; 7],
    link: Option<linkfn>,
    other_span_level_callbacks_2: [libc::size_t; 6],

    /* low level callbacks - NULL copies input directly into the output */
    entity: Option<entityfn>,
    normal_text: Option<normaltextfn>,

    /* header and footer */
    other_callbacks: [libc::size_t; 2],
}

#[repr(C)]
struct hoedown_html_renderer_state {
    opaque: *mut libc::c_void,
    toc_data: html_toc_data,
    flags: libc::c_uint,
    link_attributes: Option<extern "C" fn(*mut hoedown_buffer,
                                          *const hoedown_buffer,
                                          *const hoedown_renderer_data)>,
}

#[repr(C)]
struct html_toc_data {
    header_count: libc::c_int,
    current_level: libc::c_int,
    level_offset: libc::c_int,
    nesting_level: libc::c_int,
}

#[repr(C)]
struct hoedown_buffer {
    data: *const u8,
    size: libc::size_t,
    asize: libc::size_t,
    unit: libc::size_t,
}

struct MyOpaque {
    dfltblk: extern "C" fn(*mut hoedown_buffer, *const hoedown_buffer,
                           *const hoedown_buffer, *const hoedown_renderer_data,
                           libc::size_t),
    toc_builder: Option<TocBuilder>,
}

extern {
    fn hoedown_html_renderer_new(render_flags: libc::c_uint,
                                 nesting_level: libc::c_int)
        -> *mut hoedown_renderer;
    fn hoedown_html_renderer_free(renderer: *mut hoedown_renderer);

    fn hoedown_document_new(rndr: *const hoedown_renderer,
                            extensions: libc::c_uint,
                            max_nesting: libc::size_t) -> *mut hoedown_document;
    fn hoedown_document_render(doc: *mut hoedown_document,
                               ob: *mut hoedown_buffer,
                               document: *const u8,
                               doc_size: libc::size_t);
    fn hoedown_document_free(md: *mut hoedown_document);

    fn hoedown_buffer_new(unit: libc::size_t) -> *mut hoedown_buffer;
    fn hoedown_buffer_puts(b: *mut hoedown_buffer, c: *const libc::c_char);
    fn hoedown_buffer_free(b: *mut hoedown_buffer);
    fn hoedown_buffer_put(b: *mut hoedown_buffer, c: *const libc::c_char, len: libc::size_t);
}

impl hoedown_buffer {
    fn as_bytes(&self) -> &[u8] {
        unsafe { slice::from_raw_parts(self.data, self.size as usize) }
    }
}

pub fn render(w: &mut fmt::Formatter,
              s: &str,
              print_toc: bool,
              html_flags: libc::c_uint) -> fmt::Result {
    extern fn block(ob: *mut hoedown_buffer, orig_text: *const hoedown_buffer,
                    lang: *const hoedown_buffer, data: *const hoedown_renderer_data,
                    line: libc::size_t) {
        unsafe {
            if orig_text.is_null() { return }

            let opaque = (*data).opaque as *mut hoedown_html_renderer_state;
            let my_opaque: &MyOpaque = &*((*opaque).opaque as *const MyOpaque);
            let text = (*orig_text).as_bytes();
            let origtext = str::from_utf8(text).unwrap();
            let origtext = origtext.trim_left();
            debug!("docblock: ==============\n{:?}\n=======", text);
            let rendered = if lang.is_null() || origtext.is_empty() {
                false
            } else {
                let rlang = (*lang).as_bytes();
                let rlang = str::from_utf8(rlang).unwrap();
                if !LangString::parse(rlang).rust {
                    (my_opaque.dfltblk)(ob, orig_text, lang,
                                        opaque as *const hoedown_renderer_data,
                                        line);
                    true
                } else {
                    false
                }
            };

            let lines = origtext.lines().filter_map(|l| map_line(l).for_html());
            let text = lines.collect::<Vec<&str>>().join("\n");
            if rendered { return }
            PLAYGROUND.with(|play| {
                // insert newline to clearly separate it from the
                // previous block so we can shorten the html output
                let mut s = String::from("\n");
                let playground_button = play.borrow().as_ref().and_then(|&(ref krate, ref url)| {
                    if url.is_empty() {
                        return None;
                    }
                    let test = origtext.lines()
                        .map(|l| map_line(l).for_code())
                        .collect::<Vec<&str>>().join("\n");
                    let krate = krate.as_ref().map(|s| &**s);
                    let test = test::maketest(&test, krate, false,
                                              &Default::default());
                    let channel = if test.contains("#![feature(") {
                        "&amp;version=nightly"
                    } else {
                        ""
                    };
                    // These characters don't need to be escaped in a URI.
                    // FIXME: use a library function for percent encoding.
                    fn dont_escape(c: u8) -> bool {
                        (b'a' <= c && c <= b'z') ||
                        (b'A' <= c && c <= b'Z') ||
                        (b'0' <= c && c <= b'9') ||
                        c == b'-' || c == b'_' || c == b'.' ||
                        c == b'~' || c == b'!' || c == b'\'' ||
                        c == b'(' || c == b')' || c == b'*'
                    }
                    let mut test_escaped = String::new();
                    for b in test.bytes() {
                        if dont_escape(b) {
                            test_escaped.push(char::from(b));
                        } else {
                            write!(test_escaped, "%{:02X}", b).unwrap();
                        }
                    }
                    Some(format!(
                        r#"<a class="test-arrow" target="_blank" href="{}?code={}{}">Run</a>"#,
                        url, test_escaped, channel
                    ))
                });
                s.push_str(&highlight::render_with_highlighting(
                               &text,
                               Some("rust-example-rendered"),
                               None,
                               playground_button.as_ref().map(String::as_str)));
                hoedown_buffer_put(ob, s.as_ptr() as *const libc::c_char, s.len());
            })
        }
    }

    extern fn header(ob: *mut hoedown_buffer, text: *const hoedown_buffer,
                     level: libc::c_int, data: *const hoedown_renderer_data,
                     _: libc::size_t) {
        // hoedown does this, we may as well too
        unsafe { hoedown_buffer_puts(ob, "\n\0".as_ptr() as *const _); }

        // Extract the text provided
        let s = if text.is_null() {
            "".to_owned()
        } else {
            let s = unsafe { (*text).as_bytes() };
            str::from_utf8(&s).unwrap().to_owned()
        };

        // Discard '<em>', '<code>' tags and some escaped characters,
        // transform the contents of the header into a hyphenated string
        // without non-alphanumeric characters other than '-' and '_'.
        //
        // This is a terrible hack working around how hoedown gives us rendered
        // html for text rather than the raw text.
        let mut id = s.clone();
        let repl_sub = vec!["<em>", "</em>", "<code>", "</code>",
                            "<strong>", "</strong>",
                            "&lt;", "&gt;", "&amp;", "&#39;", "&quot;"];
        for sub in repl_sub {
            id = id.replace(sub, "");
        }
        let id = id.chars().filter_map(|c| {
            if c.is_alphanumeric() || c == '-' || c == '_' {
                if c.is_ascii() {
                    Some(c.to_ascii_lowercase())
                } else {
                    Some(c)
                }
            } else if c.is_whitespace() && c.is_ascii() {
                Some('-')
            } else {
                None
            }
        }).collect::<String>();

        let opaque = unsafe { (*data).opaque as *mut hoedown_html_renderer_state };
        let opaque = unsafe { &mut *((*opaque).opaque as *mut MyOpaque) };

        let id = derive_id(id);

        let sec = opaque.toc_builder.as_mut().map_or("".to_owned(), |builder| {
            format!("{} ", builder.push(level as u32, s.clone(), id.clone()))
        });

        // Render the HTML
        let text = format!("<h{lvl} id='{id}' class='section-header'>\
                           <a href='#{id}'>{sec}{}</a></h{lvl}>",
                           s, lvl = level, id = id, sec = sec);

        unsafe { hoedown_buffer_put(ob, text.as_ptr() as *const libc::c_char, text.len()); }
    }

    extern fn codespan(
        ob: *mut hoedown_buffer,
        text: *const hoedown_buffer,
        _: *const hoedown_renderer_data,
        _: libc::size_t
    ) -> libc::c_int {
        let content = if text.is_null() {
            "".to_owned()
        } else {
            let bytes = unsafe { (*text).as_bytes() };
            let s = str::from_utf8(bytes).unwrap();
            collapse_whitespace(s)
        };

        let content = format!("<code>{}</code>", Escape(&content)).replace("\0", "\\0");
        unsafe {
            hoedown_buffer_put(ob, content.as_ptr() as *const libc::c_char, content.len());
        }
        // Return anything except 0, which would mean "also print the code span verbatim".
        1
    }

    unsafe {
        let ob = hoedown_buffer_new(DEF_OUNIT);
        let renderer = hoedown_html_renderer_new(html_flags, 0);
        let mut opaque = MyOpaque {
            dfltblk: (*renderer).blockcode.unwrap(),
            toc_builder: if print_toc {Some(TocBuilder::new())} else {None}
        };
        (*((*renderer).opaque as *mut hoedown_html_renderer_state)).opaque
                = &mut opaque as *mut _ as *mut libc::c_void;
        (*renderer).blockcode = Some(block);
        (*renderer).header = Some(header);
        (*renderer).codespan = Some(codespan);

        let document = hoedown_document_new(renderer, HOEDOWN_EXTENSIONS, 16);
        hoedown_document_render(document, ob, s.as_ptr(),
                                s.len() as libc::size_t);
        hoedown_document_free(document);

        hoedown_html_renderer_free(renderer);

        let mut ret = opaque.toc_builder.map_or(Ok(()), |builder| {
            write!(w, "<nav id=\"TOC\">{}</nav>", builder.into_toc())
        });

        if ret.is_ok() {
            let buf = (*ob).as_bytes();
            ret = w.write_str(str::from_utf8(buf).unwrap());
        }
        hoedown_buffer_free(ob);
        ret
    }
}

pub fn old_find_testable_code(doc: &str, tests: &mut ::test::Collector, position: Span) {
    extern fn block(_ob: *mut hoedown_buffer,
                    text: *const hoedown_buffer,
                    lang: *const hoedown_buffer,
                    data: *const hoedown_renderer_data,
                    line: libc::size_t) {
        unsafe {
            if text.is_null() { return }
            let block_info = if lang.is_null() {
                LangString::all_false()
            } else {
                let lang = (*lang).as_bytes();
                let s = str::from_utf8(lang).unwrap();
                LangString::parse(s)
            };
            if !block_info.rust { return }
            let text = (*text).as_bytes();
            let opaque = (*data).opaque as *mut hoedown_html_renderer_state;
            let tests = &mut *((*opaque).opaque as *mut ::test::Collector);
            let text = str::from_utf8(text).unwrap();
            let lines = text.lines().map(|l| map_line(l).for_code());
            let text = lines.collect::<Vec<&str>>().join("\n");
            let filename = tests.get_filename();

            if tests.render_type == RenderType::Hoedown {
                let line = tests.get_line() + line;
                tests.add_test(text.to_owned(),
                               block_info.should_panic, block_info.no_run,
                               block_info.ignore, block_info.test_harness,
                               block_info.compile_fail, block_info.error_codes,
                               line, filename, block_info.allow_fail);
            } else {
                tests.add_old_test(text, filename);
            }
        }
    }

    extern fn header(_ob: *mut hoedown_buffer,
                     text: *const hoedown_buffer,
                     level: libc::c_int, data: *const hoedown_renderer_data,
                     _: libc::size_t) {
        unsafe {
            let opaque = (*data).opaque as *mut hoedown_html_renderer_state;
            let tests = &mut *((*opaque).opaque as *mut ::test::Collector);
            if text.is_null() {
                tests.register_header("", level as u32);
            } else {
                let text = (*text).as_bytes();
                let text = str::from_utf8(text).unwrap();
                tests.register_header(text, level as u32);
            }
        }
    }

    tests.set_position(position);
    unsafe {
        let ob = hoedown_buffer_new(DEF_OUNIT);
        let renderer = hoedown_html_renderer_new(0, 0);
        (*renderer).blockcode = Some(block);
        (*renderer).header = Some(header);
        (*((*renderer).opaque as *mut hoedown_html_renderer_state)).opaque
                = tests as *mut _ as *mut libc::c_void;

        let document = hoedown_document_new(renderer, HOEDOWN_EXTENSIONS, 16);
        hoedown_document_render(document, ob, doc.as_ptr(),
                                doc.len() as libc::size_t);
        hoedown_document_free(document);

        hoedown_html_renderer_free(renderer);
        hoedown_buffer_free(ob);
    }
}

pub fn find_testable_code(doc: &str, tests: &mut ::test::Collector, position: Span) {
    tests.set_position(position);

    let mut parser = Parser::new(doc);
    let mut prev_offset = 0;
    let mut nb_lines = 0;
    let mut register_header = None;
    'main: while let Some(event) = parser.next() {
        match event {
            Event::Start(Tag::CodeBlock(s)) => {
                let block_info = if s.is_empty() {
                    LangString::all_false()
                } else {
                    LangString::parse(&*s)
                };
                if !block_info.rust {
                    continue
                }
                let mut test_s = String::new();
                let mut offset = None;
                loop {
                    let event = parser.next();
                    if let Some(event) = event {
                        match event {
                            Event::End(Tag::CodeBlock(_)) => break,
                            Event::Text(ref s) => {
                                test_s.push_str(s);
                                if offset.is_none() {
                                    offset = Some(parser.get_offset());
                                }
                            }
                            _ => {}
                        }
                    } else {
                        break 'main;
                    }
                }
                let offset = offset.unwrap_or(0);
                let lines = test_s.lines().map(|l| map_line(l).for_code());
                let text = lines.collect::<Vec<&str>>().join("\n");
                nb_lines += doc[prev_offset..offset].lines().count();
                let line = tests.get_line() + (nb_lines - 1);
                let filename = tests.get_filename();
                tests.add_test(text.to_owned(),
                               block_info.should_panic, block_info.no_run,
                               block_info.ignore, block_info.test_harness,
                               block_info.compile_fail, block_info.error_codes,
                               line, filename, block_info.allow_fail);
                prev_offset = offset;
            }
            Event::Start(Tag::Header(level)) => {
                register_header = Some(level as u32);
            }
            Event::Text(ref s) if register_header.is_some() => {
                let level = register_header.unwrap();
                if s.is_empty() {
                    tests.register_header("", level);
                } else {
                    tests.register_header(s, level);
                }
                register_header = None;
            }
            _ => {}
        }
    }
}

#[derive(Eq, PartialEq, Clone, Debug)]
struct LangString {
    original: String,
    should_panic: bool,
    no_run: bool,
    ignore: bool,
    rust: bool,
    test_harness: bool,
    compile_fail: bool,
    error_codes: Vec<String>,
    allow_fail: bool,
}

impl LangString {
    fn all_false() -> LangString {
        LangString {
            original: String::new(),
            should_panic: false,
            no_run: false,
            ignore: false,
            rust: true,  // NB This used to be `notrust = false`
            test_harness: false,
            compile_fail: false,
            error_codes: Vec::new(),
            allow_fail: false,
        }
    }

    fn parse(string: &str) -> LangString {
        let mut seen_rust_tags = false;
        let mut seen_other_tags = false;
        let mut data = LangString::all_false();
        let mut allow_compile_fail = false;
        let mut allow_error_code_check = false;
        if UnstableFeatures::from_environment().is_nightly_build() {
            allow_compile_fail = true;
            allow_error_code_check = true;
        }

        data.original = string.to_owned();
        let tokens = string.split(|c: char|
            !(c == '_' || c == '-' || c.is_alphanumeric())
        );

        for token in tokens {
            match token.trim() {
                "" => {},
                "should_panic" => {
                    data.should_panic = true;
                    seen_rust_tags = seen_other_tags == false;
                }
                "no_run" => { data.no_run = true; seen_rust_tags = !seen_other_tags; }
                "ignore" => { data.ignore = true; seen_rust_tags = !seen_other_tags; }
                "allow_fail" => { data.allow_fail = true; seen_rust_tags = !seen_other_tags; }
                "rust" => { data.rust = true; seen_rust_tags = true; }
                "test_harness" => {
                    data.test_harness = true;
                    seen_rust_tags = !seen_other_tags || seen_rust_tags;
                }
                "compile_fail" if allow_compile_fail => {
                    data.compile_fail = true;
                    seen_rust_tags = !seen_other_tags || seen_rust_tags;
                    data.no_run = true;
                }
                x if allow_error_code_check && x.starts_with("E") && x.len() == 5 => {
                    if let Ok(_) = x[1..].parse::<u32>() {
                        data.error_codes.push(x.to_owned());
                        seen_rust_tags = !seen_other_tags || seen_rust_tags;
                    } else {
                        seen_other_tags = true;
                    }
                }
                _ => { seen_other_tags = true }
            }
        }

        data.rust &= !seen_other_tags || seen_rust_tags;

        data
    }
}

impl<'a> fmt::Display for Markdown<'a> {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        let Markdown(md, render_type) = *self;

        // This is actually common enough to special-case
        if md.is_empty() { return Ok(()) }
        if render_type == RenderType::Hoedown {
            render(fmt, md, false, 0)
        } else {
            let mut opts = Options::empty();
            opts.insert(OPTION_ENABLE_TABLES);
            opts.insert(OPTION_ENABLE_FOOTNOTES);

            let p = Parser::new_ext(md, opts);

            let mut s = String::with_capacity(md.len() * 3 / 2);

            html::push_html(&mut s,
                            Footnotes::new(CodeBlocks::new(HeadingLinks::new(p, None))));

            fmt.write_str(&s)
        }
    }
}

impl<'a> fmt::Display for MarkdownWithToc<'a> {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        let MarkdownWithToc(md, render_type) = *self;

        if render_type == RenderType::Hoedown {
            render(fmt, md, true, 0)
        } else {
            let mut opts = Options::empty();
            opts.insert(OPTION_ENABLE_TABLES);
            opts.insert(OPTION_ENABLE_FOOTNOTES);

            let p = Parser::new_ext(md, opts);

            let mut s = String::with_capacity(md.len() * 3 / 2);

            let mut toc = TocBuilder::new();

            html::push_html(&mut s,
                            Footnotes::new(CodeBlocks::new(HeadingLinks::new(p, Some(&mut toc)))));

            write!(fmt, "<nav id=\"TOC\">{}</nav>", toc.into_toc())?;

            fmt.write_str(&s)
        }
    }
}

impl<'a> fmt::Display for MarkdownHtml<'a> {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        let MarkdownHtml(md, render_type) = *self;

        // This is actually common enough to special-case
        if md.is_empty() { return Ok(()) }
        if render_type == RenderType::Hoedown {
            render(fmt, md, false, HOEDOWN_HTML_ESCAPE)
        } else {
            let mut opts = Options::empty();
            opts.insert(OPTION_ENABLE_TABLES);
            opts.insert(OPTION_ENABLE_FOOTNOTES);

            let p = Parser::new_ext(md, opts);

            // Treat inline HTML as plain text.
            let p = p.map(|event| match event {
                Event::Html(text) | Event::InlineHtml(text) => Event::Text(text),
                _ => event
            });

            let mut s = String::with_capacity(md.len() * 3 / 2);

            html::push_html(&mut s,
                            Footnotes::new(CodeBlocks::new(HeadingLinks::new(p, None))));

            fmt.write_str(&s)
        }
    }
}

impl<'a> fmt::Display for MarkdownSummaryLine<'a> {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        let MarkdownSummaryLine(md) = *self;
        // This is actually common enough to special-case
        if md.is_empty() { return Ok(()) }

        let p = Parser::new(md);

        let mut s = String::new();

        html::push_html(&mut s, SummaryLine::new(p));

        fmt.write_str(&s)
    }
}

pub fn plain_summary_line(md: &str) -> String {
    struct ParserWrapper<'a> {
        inner: Parser<'a>,
        is_in: isize,
        is_first: bool,
    }

    impl<'a> Iterator for ParserWrapper<'a> {
        type Item = String;

        fn next(&mut self) -> Option<String> {
            let next_event = self.inner.next();
            if next_event.is_none() {
                return None
            }
            let next_event = next_event.unwrap();
            let (ret, is_in) = match next_event {
                Event::Start(Tag::Paragraph) => (None, 1),
                Event::Start(Tag::Code) => (Some("`".to_owned()), 1),
                Event::End(Tag::Code) => (Some("`".to_owned()), -1),
                Event::Start(Tag::Header(_)) => (None, 1),
                Event::Text(ref s) if self.is_in > 0 => (Some(s.as_ref().to_owned()), 0),
                Event::End(Tag::Paragraph) | Event::End(Tag::Header(_)) => (None, -1),
                _ => (None, 0),
            };
            if is_in > 0 || (is_in < 0 && self.is_in > 0) {
                self.is_in += is_in;
            }
            if ret.is_some() {
                self.is_first = false;
                ret
            } else {
                Some(String::new())
            }
        }
    }
    let mut s = String::with_capacity(md.len() * 3 / 2);
    let mut p = ParserWrapper {
        inner: Parser::new(md),
        is_in: 0,
        is_first: true,
    };
    while let Some(t) = p.next() {
        if !t.is_empty() {
            s.push_str(&t);
        }
    }
    s
}

#[cfg(test)]
mod tests {
    use super::{LangString, Markdown, MarkdownHtml};
    use super::plain_summary_line;
    use super::RenderType;
    use html::render::reset_ids;

    #[test]
    fn test_lang_string_parse() {
        fn t(s: &str,
            should_panic: bool, no_run: bool, ignore: bool, rust: bool, test_harness: bool,
            compile_fail: bool, allow_fail: bool, error_codes: Vec<String>) {
            assert_eq!(LangString::parse(s), LangString {
                should_panic: should_panic,
                no_run: no_run,
                ignore: ignore,
                rust: rust,
                test_harness: test_harness,
                compile_fail: compile_fail,
                error_codes: error_codes,
                original: s.to_owned(),
                allow_fail: allow_fail,
            })
        }

        fn v() -> Vec<String> {
            Vec::new()
        }

        // marker                | should_panic| no_run| ignore| rust | test_harness| compile_fail
        //                       | allow_fail | error_codes
        t("",                      false,        false,  false,  true,  false, false, false, v());
        t("rust",                  false,        false,  false,  true,  false, false, false, v());
        t("sh",                    false,        false,  false,  false, false, false, false, v());
        t("ignore",                false,        false,  true,   true,  false, false, false, v());
        t("should_panic",          true,         false,  false,  true,  false, false, false, v());
        t("no_run",                false,        true,   false,  true,  false, false, false, v());
        t("test_harness",          false,        false,  false,  true,  true,  false, false, v());
        t("compile_fail",          false,        true,   false,  true,  false, true,  false, v());
        t("allow_fail",            false,        false,  false,  true,  false, false, true,  v());
        t("{.no_run .example}",    false,        true,   false,  true,  false, false, false, v());
        t("{.sh .should_panic}",   true,         false,  false,  false, false, false, false, v());
        t("{.example .rust}",      false,        false,  false,  true,  false, false, false, v());
        t("{.test_harness .rust}", false,        false,  false,  true,  true,  false, false, v());
        t("text, no_run",          false,        true,   false,  false, false, false, false, v());
        t("text,no_run",           false,        true,   false,  false, false, false, false, v());
    }

    #[test]
    fn issue_17736() {
        let markdown = "# title";
        format!("{}", Markdown(markdown, RenderType::Pulldown));
        reset_ids(true);
    }

    #[test]
    fn test_header() {
        fn t(input: &str, expect: &str) {
            let output = format!("{}", Markdown(input, RenderType::Pulldown));
            assert_eq!(output, expect, "original: {}", input);
            reset_ids(true);
        }

        t("# Foo bar", "<h1 id=\"foo-bar\" class=\"section-header\">\
          <a href=\"#foo-bar\">Foo bar</a></h1>");
        t("## Foo-bar_baz qux", "<h2 id=\"foo-bar_baz-qux\" class=\"section-\
          header\"><a href=\"#foo-bar_baz-qux\">Foo-bar_baz qux</a></h2>");
        t("### **Foo** *bar* baz!?!& -_qux_-%",
          "<h3 id=\"foo-bar-baz--qux-\" class=\"section-header\">\
          <a href=\"#foo-bar-baz--qux-\"><strong>Foo</strong> \
          <em>bar</em> baz!?!&amp; -<em>qux</em>-%</a></h3>");
        t("#### **Foo?** & \\*bar?!*  _`baz`_ ❤ #qux",
          "<h4 id=\"foo--bar--baz--qux\" class=\"section-header\">\
          <a href=\"#foo--bar--baz--qux\"><strong>Foo?</strong> &amp; *bar?!*  \
          <em><code>baz</code></em> ❤ #qux</a></h4>");
    }

    #[test]
    fn test_header_ids_multiple_blocks() {
        fn t(input: &str, expect: &str) {
            let output = format!("{}", Markdown(input, RenderType::Pulldown));
            assert_eq!(output, expect, "original: {}", input);
        }

        let test = || {
            t("# Example", "<h1 id=\"example\" class=\"section-header\">\
              <a href=\"#example\">Example</a></h1>");
            t("# Panics", "<h1 id=\"panics\" class=\"section-header\">\
              <a href=\"#panics\">Panics</a></h1>");
            t("# Example", "<h1 id=\"example-1\" class=\"section-header\">\
              <a href=\"#example-1\">Example</a></h1>");
            t("# Main", "<h1 id=\"main-1\" class=\"section-header\">\
              <a href=\"#main-1\">Main</a></h1>");
            t("# Example", "<h1 id=\"example-2\" class=\"section-header\">\
              <a href=\"#example-2\">Example</a></h1>");
            t("# Panics", "<h1 id=\"panics-1\" class=\"section-header\">\
              <a href=\"#panics-1\">Panics</a></h1>");
        };
        test();
        reset_ids(true);
        test();
    }

    #[test]
    fn test_plain_summary_line() {
        fn t(input: &str, expect: &str) {
            let output = plain_summary_line(input);
            assert_eq!(output, expect, "original: {}", input);
        }

        t("hello [Rust](https://www.rust-lang.org) :)", "hello Rust :)");
        t("hello [Rust](https://www.rust-lang.org \"Rust\") :)", "hello Rust :)");
        t("code `let x = i32;` ...", "code `let x = i32;` ...");
        t("type `Type<'static>` ...", "type `Type<'static>` ...");
        t("# top header", "top header");
        t("## header", "header");
    }

    #[test]
    fn test_markdown_html_escape() {
        fn t(input: &str, expect: &str) {
            let output = format!("{}", MarkdownHtml(input, RenderType::Pulldown));
            assert_eq!(output, expect, "original: {}", input);
        }

        t("`Struct<'a, T>`", "<p><code>Struct&lt;'a, T&gt;</code></p>\n");
        t("Struct<'a, T>", "<p>Struct&lt;'a, T&gt;</p>\n");
        t("Struct<br>", "<p>Struct&lt;br&gt;</p>\n");
    }
}