Merge pull request #335 from Michael-F-Bryan/refactor-hbs-renderer

Refactor hbs renderer

src/renderer/html_handlebars/hbs_renderer.rs

@@ -1,8 +1,9 @@
 use renderer::html_handlebars::helpers;
 use renderer::Renderer;
 use book::MDBook;
-use book::bookitem::BookItem;
-use {utils, theme};
+use book::bookitem::{BookItem, Chapter};
+use utils;
+use theme::{self, Theme};
 use regex::{Regex, Captures};
 
 use std::ascii::AsciiExt;
@@ -25,197 +26,276 @@ impl HtmlHandlebars {
     pub fn new() -> Self {
         HtmlHandlebars
     }
+
+    fn render_item(&self, item: &BookItem, mut ctx: RenderItemContext, print_content: &mut String)
+        -> Result<(), Box<Error>> {
+        // FIXME: This should be made DRY-er and rely less on mutable state
+        match *item {
+            BookItem::Chapter(_, ref ch) |
+            BookItem::Affix(ref ch) => {
+                if ch.path != PathBuf::new() {
+
+                    let path = ctx.book.get_source().join(&ch.path);
+
+                    debug!("[*]: Opening file: {:?}", path);
+                    let mut f = File::open(&path)?;
+                    let mut content: String = String::new();
+
+                    debug!("[*]: Reading file");
+                    f.read_to_string(&mut content)?;
+
+                    // Parse for playpen links
+                    if let Some(p) = path.parent() {
+                        content = helpers::playpen::render_playpen(&content, p);
+                    }
+
+                    content = utils::render_markdown(&content, ctx.book.get_curly_quotes());
+                    print_content.push_str(&content);
+
+                    // Update the context with data for this file
+                    let path = ch.path.to_str().ok_or_else(|| {
+                        io::Error::new(io::ErrorKind::Other, "Could not convert path to str")
+                    })?;
+
+                    ctx.data.insert("path".to_owned(), json!(path));
+                    ctx.data.insert("content".to_owned(), json!(content));
+                    ctx.data.insert("chapter_title".to_owned(), json!(ch.name));
+                    ctx.data.insert(
+                        "path_to_root".to_owned(),
+                        json!(utils::fs::path_to_root(&ch.path)),
+                    );
+
+                    // Render the handlebars template with the data
+                    debug!("[*]: Render template");
+                    let rendered = ctx.handlebars.render("index", &ctx.data)?;
+                    let rendered = self.post_process(rendered);
+
+                    let filename = Path::new(&ch.path).with_extension("html");
+
+                    // Write to file
+                    info!("[*] Creating {:?} ✓", filename.display());
+                    ctx.book.write_file(filename, &rendered.into_bytes())?;
+
+                    if ctx.is_index {
+                        self.render_index(&ctx.book, ch, &ctx.destination)?;
+                    }
+                }
+            },
+            _ => {},
+        }
+
+        Ok(())
+    }
+
+    /// Create an index.html from the first element in SUMMARY.md
+    fn render_index(&self, book: &MDBook, ch: &Chapter, destination: &Path) -> Result<(), Box<Error>> {
+        debug!("[*]: index.html");
+
+        let mut content = String::new();
+
+        File::open(destination.join(&ch.path.with_extension("html")))?
+            .read_to_string(&mut content)?;
+
+        // This could cause a problem when someone displays
+        // code containing <base href=...>
+        // on the front page, however this case should be very very rare...
+        content = content
+            .lines()
+            .filter(|line| !line.contains("<base href="))
+            .collect::<Vec<&str>>()
+            .join("\n");
+
+        book.write_file("index.html", content.as_bytes())?;
+
+        info!(
+            "[*] Creating index.html from {:?} ✓",
+            book.get_destination()
+                .expect(
+                    "If the HTML renderer is called, one would assume the HtmlConfig is \
+                                            set... (4)",
+                )
+                .join(&ch.path.with_extension("html"))
+        );
+
+        Ok(())
+    }
+
+    fn post_process(&self, rendered: String) -> String {
+        let rendered = build_header_links(rendered, "print.html");
+        let rendered = fix_anchor_links(rendered, "print.html");
+        let rendered = fix_code_blocks(rendered);
+        let rendered = add_playpen_pre(rendered);
+
+        rendered
+    }
+
+    fn copy_static_files(&self, book: &MDBook, theme: &Theme) -> Result<(), Box<Error>> {
+        book.write_file("book.js", &theme.js)?;
+        book.write_file("book.css", &theme.css)?;
+        book.write_file("favicon.png", &theme.favicon)?;
+        book.write_file("jquery.js", &theme.jquery)?;
+        book.write_file("highlight.css", &theme.highlight_css)?;
+        book.write_file(
+            "tomorrow-night.css",
+            &theme.tomorrow_night_css,
+        )?;
+        book.write_file(
+            "ayu-highlight.css",
+            &theme.ayu_highlight_css,
+        )?;
+        book.write_file("highlight.js", &theme.highlight_js)?;
+        book.write_file("clipboard.min.js", &theme.clipboard_js)?;
+        book.write_file("store.js", &theme.store_js)?;
+        book.write_file(
+            "_FontAwesome/css/font-awesome.css",
+            theme::FONT_AWESOME,
+        )?;
+        book.write_file(
+            "_FontAwesome/fonts/fontawesome-webfont.eot",
+            theme::FONT_AWESOME_EOT,
+        )?;
+        book.write_file(
+            "_FontAwesome/fonts/fontawesome-webfont.svg",
+            theme::FONT_AWESOME_SVG,
+        )?;
+        book.write_file(
+            "_FontAwesome/fonts/fontawesome-webfont.ttf",
+            theme::FONT_AWESOME_TTF,
+        )?;
+        book.write_file(
+            "_FontAwesome/fonts/fontawesome-webfont.woff",
+            theme::FONT_AWESOME_WOFF,
+        )?;
+        book.write_file(
+            "_FontAwesome/fonts/fontawesome-webfont.woff2",
+            theme::FONT_AWESOME_WOFF2,
+        )?;
+        book.write_file(
+            "_FontAwesome/fonts/FontAwesome.ttf",
+            theme::FONT_AWESOME_TTF,
+        )?;
+
+        Ok(())
+    }
+
+    /// Helper function to write a file to the build directory, normalizing 
+    /// the path to be relative to the book root.
+    fn write_custom_file(&self, custom_file: &Path, book: &MDBook) -> Result<(), Box<Error>> {
+        let mut data = Vec::new();
+        let mut f = File::open(custom_file)?;
+        f.read_to_end(&mut data)?;
+
+        let name = match custom_file.strip_prefix(book.get_root()) {
+            Ok(p) => p.to_str().expect("Could not convert to str"),
+            Err(_) => {
+                custom_file
+                    .file_name()
+                    .expect("File has a file name")
+                    .to_str()
+                    .expect("Could not convert to str")
+            },
+        };
+
+        book.write_file(name, &data)?;
+
+        Ok(())
+    }
+
+    /// Update the context with data for this file
+    fn configure_print_version(&self, data: &mut serde_json::Map<String, serde_json::Value>, print_content: &str) {
+        data.insert("path".to_owned(), json!("print.md"));
+        data.insert("content".to_owned(), json!(print_content));
+        data.insert("path_to_root".to_owned(), json!(utils::fs::path_to_root(Path::new("print.md"))));
+    }
+
+    fn register_hbs_helpers(&self, handlebars: &mut Handlebars) {
+        handlebars.register_helper("toc", Box::new(helpers::toc::RenderToc));
+        handlebars.register_helper("previous", Box::new(helpers::navigation::previous));
+        handlebars.register_helper("next", Box::new(helpers::navigation::next));
+    }
+
+    /// Copy across any additional CSS and JavaScript files which the book
+    /// has been configured to use.
+    fn copy_additional_css_and_js(&self, book: &MDBook) -> Result<(), Box<Error>> {
+        let custom_files = book.get_additional_css().iter().chain(
+            book.get_additional_js()
+                .iter(),
+        );
+
+        for custom_file in custom_files {
+            self.write_custom_file(custom_file, book)?;
+        }
+
+        Ok(())
+    }
 }
 
+
 impl Renderer for HtmlHandlebars {
     fn render(&self, book: &MDBook) -> Result<(), Box<Error>> {
         debug!("[fn]: render");
         let mut handlebars = Handlebars::new();
 
-        // Load theme
         let theme = theme::Theme::new(book.get_theme_path());
 
-        // Register template
         debug!("[*]: Register handlebars template");
-        handlebars
-            .register_template_string("index", String::from_utf8(theme.index)?)?;
+        handlebars.register_template_string(
+            "index",
+            String::from_utf8(theme.index.clone())?,
+        )?;
 
-        // Register helpers
         debug!("[*]: Register handlebars helpers");
-        handlebars.register_helper("toc", Box::new(helpers::toc::RenderToc));
-        handlebars.register_helper("previous", Box::new(helpers::navigation::previous));
-        handlebars.register_helper("next", Box::new(helpers::navigation::next));
+        self.register_hbs_helpers(&mut handlebars);
 
         let mut data = make_data(book)?;
 
         // Print version
-        let mut print_content: String = String::new();
+        let mut print_content = String::new();
+
+        let destination = book.get_destination().expect(
+            "If the HTML renderer is called, one would assume the HtmlConfig is set... (2)",
+        );
 
-        // Check if dest directory exists
         debug!("[*]: Check if destination directory exists");
-        if fs::create_dir_all(book.get_destination().expect("If the HTML renderer is called, one would assume the HtmlConfig is set... (2)")).is_err() {
-            return Err(Box::new(io::Error::new(io::ErrorKind::Other,
-                                               "Unexpected error when constructing destination path")));
+        if fs::create_dir_all(&destination).is_err() {
+            return Err(Box::new(
+                io::Error::new(io::ErrorKind::Other, "Unexpected error when constructing destination path"),
+            ));
         }
 
-        // Render a file for every entry in the book
-        let mut index = true;
-        for item in book.iter() {
-
-            match *item {
-                BookItem::Chapter(_, ref ch) |
-                BookItem::Affix(ref ch) => {
-                    if ch.path != PathBuf::new() {
-
-                        let path = book.get_source().join(&ch.path);
-
-                        debug!("[*]: Opening file: {:?}", path);
-                        let mut f = File::open(&path)?;
-                        let mut content: String = String::new();
-
-                        debug!("[*]: Reading file");
-                        f.read_to_string(&mut content)?;
-
-                        // Parse for playpen links
-                        if let Some(p) = path.parent() {
-                            content = helpers::playpen::render_playpen(&content, p);
-                        }
-
-                        // Render markdown using the pulldown-cmark crate
-                        content = utils::render_markdown(&content, book.get_curly_quotes());
-                        print_content.push_str(&content);
-
-                        // Update the context with data for this file
-                        let path =
-                            ch.path
-                                .to_str()
-                                .ok_or_else(|| io::Error::new(io::ErrorKind::Other, "Could not convert path to str"))?;
-                        data.insert("path".to_owned(), json!(path));
-                        data.insert("content".to_owned(), json!(content));
-                        data.insert("chapter_title".to_owned(), json!(ch.name));
-                        data.insert("path_to_root".to_owned(), json!(utils::fs::path_to_root(&ch.path)));
-
-                        // Render the handlebars template with the data
-                        debug!("[*]: Render template");
-                        let rendered = handlebars.render("index", &data)?;
-
-                        let filename = Path::new(&ch.path).with_extension("html");
-
-                        // Do several kinds of post-processing
-                        let rendered = build_header_links(rendered, filename.to_str().unwrap_or(""));
-                        let rendered = fix_anchor_links(rendered, filename.to_str().unwrap_or(""));
-                        let rendered = fix_code_blocks(rendered);
-                        let rendered = add_playpen_pre(rendered);
-
-                        // Write to file
-                        info!("[*] Creating {:?} ✓", filename.display());
-                        book.write_file(filename, &rendered.into_bytes())?;
-
-                        // Create an index.html from the first element in SUMMARY.md
-                        if index {
-                            debug!("[*]: index.html");
-
-                            let mut content = String::new();
-
-                            let _source = File::open(
-                                book.get_destination()
-                                    .expect("If the HTML renderer is called, one would assume the HtmlConfig is set... (3)")
-                                    .join(&ch.path.with_extension("html"))
-                            )?.read_to_string(&mut content);
-
-                            // This could cause a problem when someone displays
-                            // code containing <base href=...>
-                            // on the front page, however this case should be very very rare...
-                            content = content
-                                .lines()
-                                .filter(|line| !line.contains("<base href="))
-                                .collect::<Vec<&str>>()
-                                .join("\n");
-
-                            book.write_file("index.html", content.as_bytes())?;
-
-                            info!("[*] Creating index.html from {:?} ✓",
-                                  book.get_destination()
-                                      .expect("If the HTML renderer is called, one would assume the HtmlConfig is set... (4)")
-                                      .join(&ch.path.with_extension("html"))
-                            );
-                            index = false;
-                        }
-                    }
-                },
-                _ => {},
-            }
+        for (i, item) in book.iter().enumerate() {
+            let ctx = RenderItemContext {
+                book: book,
+                handlebars: &handlebars,
+                destination: destination.to_path_buf(),
+                data: data.clone(),
+                is_index: i == 0,
+            };
+            self.render_item(item, ctx, &mut print_content)?;
         }
 
         // Print version
-
-        // Update the context with data for this file
-        data.insert("path".to_owned(), json!("print.md"));
-        data.insert("content".to_owned(), json!(print_content));
-        data.insert("path_to_root".to_owned(), json!(utils::fs::path_to_root("print.md")));
+        self.configure_print_version(&mut data, &print_content);
 
         // Render the handlebars template with the data
         debug!("[*]: Render template");
 
         let rendered = handlebars.render("index", &data)?;
+        let rendered = self.post_process(rendered);
 
-        // do several kinds of post-processing
-        let rendered = build_header_links(rendered, "print.html");
-        let rendered = fix_anchor_links(rendered, "print.html");
-        let rendered = fix_code_blocks(rendered);
-        let rendered = add_playpen_pre(rendered);
-
-        book.write_file(Path::new("print").with_extension("html"), &rendered.into_bytes())?;
+        book.write_file(
+            Path::new("print").with_extension("html"),
+            &rendered.into_bytes(),
+        )?;
         info!("[*] Creating print.html ✓");
 
         // Copy static files (js, css, images, ...)
-
         debug!("[*] Copy static files");
-        book.write_file("book.js", &theme.js)?;
-        book.write_file("book.css", &theme.css)?;
-        book.write_file("favicon.png", &theme.favicon)?;
-        book.write_file("jquery.js", &theme.jquery)?;
-        book.write_file("highlight.css", &theme.highlight_css)?;
-        book.write_file("tomorrow-night.css", &theme.tomorrow_night_css)?;
-        book.write_file("ayu-highlight.css", &theme.ayu_highlight_css)?;
-        book.write_file("highlight.js", &theme.highlight_js)?;
-        book.write_file("clipboard.min.js", &theme.clipboard_js)?;
-        book.write_file("store.js", &theme.store_js)?;
-        book.write_file("_FontAwesome/css/font-awesome.css", theme::FONT_AWESOME)?;
-        book.write_file("_FontAwesome/fonts/fontawesome-webfont.eot", theme::FONT_AWESOME_EOT)?;
-        book.write_file("_FontAwesome/fonts/fontawesome-webfont.svg", theme::FONT_AWESOME_SVG)?;
-        book.write_file("_FontAwesome/fonts/fontawesome-webfont.ttf", theme::FONT_AWESOME_TTF)?;
-        book.write_file("_FontAwesome/fonts/fontawesome-webfont.woff", theme::FONT_AWESOME_WOFF)?;
-        book.write_file("_FontAwesome/fonts/fontawesome-webfont.woff2", theme::FONT_AWESOME_WOFF2)?;
-        book.write_file("_FontAwesome/fonts/FontAwesome.ttf", theme::FONT_AWESOME_TTF)?;
-
-        for custom_file in book.get_additional_css()
-                .iter()
-                .chain(book.get_additional_js().iter()) {
-            let mut data = Vec::new();
-            let mut f = File::open(custom_file)?;
-            f.read_to_end(&mut data)?;
-
-            let name = match custom_file.strip_prefix(book.get_root()) {
-                Ok(p) => p.to_str().expect("Could not convert to str"),
-                Err(_) => {
-                    custom_file
-                        .file_name()
-                        .expect("File has a file name")
-                        .to_str()
-                        .expect("Could not convert to str")
-                }
-            };
-
-            book.write_file(name, &data)?;
-        }
+        self.copy_static_files(book, &theme)?;
+        self.copy_additional_css_and_js(book)?;
 
         // Copy all remaining files
-        utils::fs::copy_files_except_ext(
-            book.get_source(), 
-            book.get_destination()
-                .expect("If the HTML renderer is called, one would assume the HtmlConfig is set... (5)"), true, &["md"]
-        )?;
+        utils::fs::copy_files_except_ext(book.get_source(), &destination, true, &["md"])?;
 
         Ok(())
     }
@@ -244,7 +324,15 @@ fn make_data(book: &MDBook) -> Result<serde_json::Map<String, serde_json::Value>
         for style in book.get_additional_css() {
             match style.strip_prefix(book.get_root()) {
                 Ok(p) => css.push(p.to_str().expect("Could not convert to str")),
-                Err(_) => css.push(style.file_name().expect("File has a file name").to_str().expect("Could not convert to str")),
+                Err(_) => {
+                    css.push(
+                        style
+                            .file_name()
+                            .expect("File has a file name")
+                            .to_str()
+                            .expect("Could not convert to str"),
+                    )
+                },
             }
         }
         data.insert("additional_css".to_owned(), json!(css));
@@ -256,7 +344,15 @@ fn make_data(book: &MDBook) -> Result<serde_json::Map<String, serde_json::Value>
         for script in book.get_additional_js() {
             match script.strip_prefix(book.get_root()) {
                 Ok(p) => js.push(p.to_str().expect("Could not convert to str")),
-                Err(_) => js.push(script.file_name().expect("File has a file name").to_str().expect("Could not convert to str")),
+                Err(_) => {
+                    js.push(
+                        script
+                            .file_name()
+                            .expect("File has a file name")
+                            .to_str()
+                            .expect("Could not convert to str"),
+                    )
+                },
             }
         }
         data.insert("additional_js".to_owned(), json!(js));
@@ -271,17 +367,17 @@ fn make_data(book: &MDBook) -> Result<serde_json::Map<String, serde_json::Value>
         match *item {
             BookItem::Affix(ref ch) => {
                 chapter.insert("name".to_owned(), json!(ch.name));
-                let path = ch.path
-                    .to_str()
-                    .ok_or_else(|| io::Error::new(io::ErrorKind::Other, "Could not convert path to str"))?;
+                let path = ch.path.to_str().ok_or_else(|| {
+                    io::Error::new(io::ErrorKind::Other, "Could not convert path to str")
+                })?;
                 chapter.insert("path".to_owned(), json!(path));
             },
             BookItem::Chapter(ref s, ref ch) => {
                 chapter.insert("section".to_owned(), json!(s));
                 chapter.insert("name".to_owned(), json!(ch.name));
-                let path = ch.path
-                    .to_str()
-                    .ok_or_else(|| io::Error::new(io::ErrorKind::Other, "Could not convert path to str"))?;
+                let path = ch.path.to_str().ok_or_else(|| {
+                    io::Error::new(io::ErrorKind::Other, "Could not convert path to str")
+                })?;
                 chapter.insert("path".to_owned(), json!(path));
             },
             BookItem::Spacer => {
@@ -299,61 +395,83 @@ fn make_data(book: &MDBook) -> Result<serde_json::Map<String, serde_json::Value>
     Ok(data)
 }
 
+/// Goes through the rendered HTML, making sure all header tags are wrapped in
+/// an anchor so people can link to sections directly.
 fn build_header_links(html: String, filename: &str) -> String {
     let regex = Regex::new(r"<h(\d)>(.*?)</h\d>").unwrap();
     let mut id_counter = HashMap::new();
 
     regex
         .replace_all(&html, |caps: &Captures| {
-            let level = &caps[1];
-            let text = &caps[2];
-            let mut id = text.to_string();
-            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 level = caps[1].parse().expect(
+                "Regex should ensure we only ever get numbers here",
+            );
 
-            let id_count = *id_counter.get(&id).unwrap_or(&0);
-            id_counter.insert(id.clone(), id_count + 1);
-
-            let id = if id_count > 0 {
-                format!("{}-{}", id, id_count)
-            } else {
-                id
-            };
-
-            format!("<a class=\"header\" href=\"{filename}#{id}\" id=\"{id}\"><h{level}>{text}</h{level}></a>",
-                    level = level,
-                    id = id,
-                    text = text,
-                    filename = filename)
+            wrap_header_with_link(level, &caps[2], &mut id_counter, filename)
         })
         .into_owned()
 }
 
+/// Wraps a single header tag with a link, making sure each tag gets its own
+/// unique ID by appending an auto-incremented number (if necessary).
+fn wrap_header_with_link(level: usize, content: &str, id_counter: &mut HashMap<String, usize>, filename: &str)
+    -> String {
+    let raw_id = id_from_content(content);
+
+    let id_count = id_counter.entry(raw_id.clone()).or_insert(0);
+
+    let id = match *id_count {
+        0 => raw_id,
+        other => format!("{}-{}", raw_id, other),
+    };
+
+    *id_count += 1;
+
+    format!(
+        r#"<a class="header" href="{filename}#{id}" id="{id}"><h{level}>{text}</h{level}></a>"#,
+        level = level,
+        id = id,
+        text = content,
+        filename = filename
+    )
+}
+
+/// Generate an id for use with anchors which is derived from a "normalised"
+/// string.
+fn id_from_content(content: &str) -> String {
+    let mut content = content.to_string();
+
+    // Skip any tags or html-encoded stuff
+    let repl_sub = vec![
+        "<em>",
+        "</em>",
+        "<code>",
+        "</code>",
+        "<strong>",
+        "</strong>",
+        "&lt;",
+        "&gt;",
+        "&amp;",
+        "&#39;",
+        "&quot;",
+    ];
+    for sub in repl_sub {
+        content = content.replace(sub, "");
+    }
+
+    let mut id = String::new();
+
+    for c in content.chars() {
+        if c.is_alphanumeric() || c == '-' || c == '_' {
+            id.push(c.to_ascii_lowercase());
+        } else if c.is_whitespace() {
+            id.push(c);
+        }
+    }
+
+    id
+}
+
 // anchors to the same page (href="#anchor") do not work because of
 // <base href="../"> pointing to the root folder. This function *fixes*
 // that in a very inelegant way
@@ -365,11 +483,13 @@ fn fix_anchor_links(html: String, filename: &str) -> String {
             let anchor = &caps[2];
             let after = &caps[3];
 
-            format!("<a{before}href=\"{filename}#{anchor}\"{after}>",
-                    before = before,
-                    filename = filename,
-                    anchor = anchor,
-                    after = after)
+            format!(
+                "<a{before}href=\"{filename}#{anchor}\"{after}>",
+                before = before,
+                filename = filename,
+                anchor = anchor,
+                after = after
+            )
         })
         .into_owned()
 }
@@ -391,7 +511,7 @@ fn fix_code_blocks(html: String) -> String {
             let classes = &caps[2].replace(",", " ");
             let after = &caps[3];
 
-            format!("<code{before}class=\"{classes}\"{after}>", before = before, classes = classes, after = after)
+            format!(r#"<code{before}class="{classes}"{after}>"#, before = before, classes = classes, after = after)
         })
         .into_owned()
 }
@@ -412,14 +532,16 @@ fn add_playpen_pre(html: String) -> String {
                 } else {
                     // we need to inject our own main
                     let (attrs, code) = partition_source(code);
-                    format!("<pre class=\"playpen\"><code class=\"{}\"># #![allow(unused_variables)]
+                    format!(
+                        "<pre class=\"playpen\"><code class=\"{}\"># #![allow(unused_variables)]
 {}#fn main() {{
 \
                              {}
 #}}</code></pre>",
-                            classes,
-                            attrs,
-                            code)
+                        classes,
+                        attrs,
+                        code
+                    )
                 }
             } else {
                 // not language-rust, so no-op
@@ -449,3 +571,37 @@ fn partition_source(s: &str) -> (String, String) {
 
     (before, after)
 }
+
+
+struct RenderItemContext<'a> {
+    handlebars: &'a Handlebars,
+    book: &'a MDBook,
+    destination: PathBuf,
+    data: serde_json::Map<String, serde_json::Value>,
+    is_index: bool,
+}
+
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn original_build_header_links() {
+        let inputs = vec![
+            ("blah blah <h1>Foo</h1>", r#"blah blah <a class="header" href="bar.rs#foo" id="foo"><h1>Foo</h1></a>"#),
+            ("<h1>Foo</h1>", r#"<a class="header" href="bar.rs#foo" id="foo"><h1>Foo</h1></a>"#),
+            ("<h3>Foo^bar</h3>", r#"<a class="header" href="bar.rs#foobar" id="foobar"><h3>Foo^bar</h3></a>"#),
+            ("<h4></h4>", r#"<a class="header" href="bar.rs#" id=""><h4></h4></a>"#),
+            ("<h4><em>Hï</em></h4>", r#"<a class="header" href="bar.rs#hï" id="hï"><h4><em>Hï</em></h4></a>"#),
+            ("<h1>Foo</h1><h3>Foo</h3>", 
+                r#"<a class="header" href="bar.rs#foo" id="foo"><h1>Foo</h1></a><a class="header" href="bar.rs#foo-1" id="foo-1"><h3>Foo</h3></a>"#),
+        ];
+
+        for (src, should_be) in inputs {
+            let got = build_header_links(src.to_string(), "bar.rs");
+            assert_eq!(got, should_be);
+        }
+    }
+}