Load the sidebar toc from a shared JS file or iframe

src/renderer/html_handlebars/hbs_renderer.rs

@@ -528,6 +528,11 @@ impl Renderer for HtmlHandlebars {
         debug!("Register the header handlebars template");
         handlebars.register_partial("header", String::from_utf8(theme.header.clone())?)?;
 
+        debug!("Register the toc handlebars template");
+        handlebars.register_template_string("toc_js", String::from_utf8(theme.toc_js.clone())?)?;
+        handlebars
+            .register_template_string("toc_html", String::from_utf8(theme.toc_html.clone())?)?;
+
         debug!("Register handlebars helpers");
         self.register_hbs_helpers(&mut handlebars, &html_config);
 
@@ -583,6 +588,18 @@ impl Renderer for HtmlHandlebars {
             debug!("Creating print.html ✓");
         }
 
+        debug!("Render toc");
+        {
+            let rendered_toc = handlebars.render("toc_js", &data)?;
+            utils::fs::write_file(destination, "toc.js", rendered_toc.as_bytes())?;
+            debug!("Creating toc.js ✓");
+            data.insert("is_toc_html".to_owned(), json!(true));
+            let rendered_toc = handlebars.render("toc_html", &data)?;
+            utils::fs::write_file(destination, "toc.html", rendered_toc.as_bytes())?;
+            debug!("Creating toc.html ✓");
+            data.remove("is_toc_html");
+        }
+
         debug!("Copy static files");
         self.copy_static_files(destination, &theme, &html_config)
             .with_context(|| "Unable to copy across static files")?;

src/renderer/html_handlebars/helpers/toc.rs

@@ -1,8 +1,7 @@
 use std::path::Path;
 use std::{cmp::Ordering, collections::BTreeMap};
 
-use crate::utils;
-use crate::utils::bracket_escape;
+use crate::utils::special_escape;
 
 use handlebars::{
     Context, Handlebars, Helper, HelperDef, Output, RenderContext, RenderError, RenderErrorReason,
@@ -32,21 +31,6 @@ impl HelperDef for RenderToc {
                     RenderErrorReason::Other("Could not decode the JSON data".to_owned()).into()
                 })
         })?;
-        let current_path = rc
-            .evaluate(ctx, "@root/path")?
-            .as_json()
-            .as_str()
-            .ok_or_else(|| {
-                RenderErrorReason::Other("Type error for `path`, string expected".to_owned())
-            })?
-            .replace('\"', "");
-
-        let current_section = rc
-            .evaluate(ctx, "@root/section")?
-            .as_json()
-            .as_str()
-            .map(str::to_owned)
-            .unwrap_or_default();
 
         let fold_enable = rc
             .evaluate(ctx, "@root/fold_enable")?
@@ -64,31 +48,27 @@ impl HelperDef for RenderToc {
                 RenderErrorReason::Other("Type error for `fold_level`, u64 expected".to_owned())
             })?;
 
+        // If true, then this is the iframe and we need target="_parent"
+        let is_toc_html = rc
+            .evaluate(ctx, "@root/is_toc_html")?
+            .as_json()
+            .as_bool()
+            .unwrap_or(false);
+
         out.write("<ol class=\"chapter\">")?;
 
         let mut current_level = 1;
-        // The "index" page, which has this attribute set, is supposed to alias the first chapter in
-        // the book, i.e. the first link. There seems to be no easy way to determine which chapter
-        // the "index" is aliasing from within the renderer, so this is used instead to force the
-        // first link to be active. See further below.
-        let mut is_first_chapter = ctx.data().get("is_index").is_some();
 
         for item in chapters {
-            let (section, level) = if let Some(s) = item.get("section") {
+            let (_section, level) = if let Some(s) = item.get("section") {
                 (s.as_str(), s.matches('.').count())
             } else {
                 ("", 1)
             };
 
-            let is_expanded =
-                if !fold_enable || (!section.is_empty() && current_section.starts_with(section)) {
-                    // Expand if folding is disabled, or if the section is an
-                    // ancestor or the current section itself.
-                    true
-                } else {
-                    // Levels that are larger than this would be folded.
-                    level - 1 < fold_level as usize
-                };
+            // Expand if folding is disabled, or if levels that are larger than this would not
+            // be folded.
+            let is_expanded = !fold_enable || level - 1 < (fold_level as usize);
 
             match level.cmp(&current_level) {
                 Ordering::Greater => {
@@ -121,7 +101,7 @@ impl HelperDef for RenderToc {
             // Part title
             if let Some(title) = item.get("part") {
                 out.write("<li class=\"part-title\">")?;
-                out.write(&bracket_escape(title))?;
+                out.write(&special_escape(title))?;
                 out.write("</li>")?;
                 continue;
             }
@@ -139,16 +119,12 @@ impl HelperDef for RenderToc {
                         .replace('\\', "/");
 
                     // Add link
-                    out.write(&utils::fs::path_to_root(&current_path))?;
                     out.write(&tmp)?;
-                    out.write("\"")?;
-
-                    if path == &current_path || is_first_chapter {
-                        is_first_chapter = false;
-                        out.write(" class=\"active\"")?;
-                    }
-
-                    out.write(">")?;
+                    out.write(if is_toc_html {
+                        "\" target=\"_parent\">"
+                    } else {
+                        "\">"
+                    })?;
                     path_exists = true;
                 }
                 _ => {
@@ -167,7 +143,7 @@ impl HelperDef for RenderToc {
             }
 
             if let Some(name) = item.get("name") {
-                out.write(&bracket_escape(name))?
+                out.write(&special_escape(name))?
             }
 
             if path_exists {

src/theme/css/chrome.css

@@ -399,6 +399,22 @@ ul#searchresults span.teaser em {
     background-color: var(--sidebar-bg);
     color: var(--sidebar-fg);
 }
+.sidebar-iframe-inner {
+    background-color: var(--sidebar-bg);
+    color: var(--sidebar-fg);
+    padding: 10px 10px;
+    margin: 0;
+    font-size: 1.4rem;
+}
+.sidebar-iframe-outer {
+    border: none;
+    height: 100%;
+    position: absolute;
+    top: 0;
+    bottom: 0;
+    left: 0;
+    right: 0;
+}
 [dir=rtl] .sidebar { left: unset; right: 0; }
 .sidebar-resizing {
     -moz-user-select: none;

src/theme/index.hbs

@@ -109,35 +109,17 @@
         </script>
 
         <nav id="sidebar" class="sidebar" aria-label="Table of contents">
-            <div class="sidebar-scrollbox">
-                {{#toc}}{{/toc}}
-            </div>
+            <!-- populated by js -->
+            <div class="sidebar-scrollbox"></div>
+            <noscript>
+                <iframe class="sidebar-iframe-outer" src="{{ path_to_root }}toc.html"></iframe>
+            </noscript>
             <div id="sidebar-resize-handle" class="sidebar-resize-handle">
                 <div class="sidebar-resize-indicator"></div>
             </div>
         </nav>
 
-        <!-- Track and set sidebar scroll position -->
-        <script>
-            var sidebarScrollbox = document.querySelector('#sidebar .sidebar-scrollbox');
-            sidebarScrollbox.addEventListener('click', function(e) {
-                if (e.target.tagName === 'A') {
-                    sessionStorage.setItem('sidebar-scroll', sidebarScrollbox.scrollTop);
-                }
-            }, { passive: true });
-            var sidebarScrollTop = sessionStorage.getItem('sidebar-scroll');
-            sessionStorage.removeItem('sidebar-scroll');
-            if (sidebarScrollTop) {
-                // preserve sidebar scroll position when navigating via links within sidebar
-                sidebarScrollbox.scrollTop = sidebarScrollTop;
-            } else {
-                // scroll sidebar to current active section when navigating via "next/previous chapter" buttons
-                var activeSection = document.querySelector('#sidebar .active');
-                if (activeSection) {
-                    activeSection.scrollIntoView({ block: 'center' });
-                }
-            }
-        </script>
+        <script async src="{{ path_to_root }}toc.js"></script>
 
         <div id="page-wrapper" class="page-wrapper">
 

src/theme/mod.rs

@@ -17,6 +17,8 @@ pub static INDEX: &[u8] = include_bytes!("index.hbs");
 pub static HEAD: &[u8] = include_bytes!("head.hbs");
 pub static REDIRECT: &[u8] = include_bytes!("redirect.hbs");
 pub static HEADER: &[u8] = include_bytes!("header.hbs");
+pub static TOC_JS: &[u8] = include_bytes!("toc.js.hbs");
+pub static TOC_HTML: &[u8] = include_bytes!("toc.html.hbs");
 pub static CHROME_CSS: &[u8] = include_bytes!("css/chrome.css");
 pub static GENERAL_CSS: &[u8] = include_bytes!("css/general.css");
 pub static PRINT_CSS: &[u8] = include_bytes!("css/print.css");
@@ -50,6 +52,8 @@ pub struct Theme {
     pub head: Vec<u8>,
     pub redirect: Vec<u8>,
     pub header: Vec<u8>,
+    pub toc_js: Vec<u8>,
+    pub toc_html: Vec<u8>,
     pub chrome_css: Vec<u8>,
     pub general_css: Vec<u8>,
     pub print_css: Vec<u8>,
@@ -85,6 +89,8 @@ impl Theme {
                 (theme_dir.join("head.hbs"), &mut theme.head),
                 (theme_dir.join("redirect.hbs"), &mut theme.redirect),
                 (theme_dir.join("header.hbs"), &mut theme.header),
+                (theme_dir.join("toc.js.hbs"), &mut theme.toc_js),
+                (theme_dir.join("toc.html.hbs"), &mut theme.toc_html),
                 (theme_dir.join("book.js"), &mut theme.js),
                 (theme_dir.join("css/chrome.css"), &mut theme.chrome_css),
                 (theme_dir.join("css/general.css"), &mut theme.general_css),
@@ -174,6 +180,8 @@ impl Default for Theme {
             head: HEAD.to_owned(),
             redirect: REDIRECT.to_owned(),
             header: HEADER.to_owned(),
+            toc_js: TOC_JS.to_owned(),
+            toc_html: TOC_HTML.to_owned(),
             chrome_css: CHROME_CSS.to_owned(),
             general_css: GENERAL_CSS.to_owned(),
             print_css: PRINT_CSS.to_owned(),
@@ -232,6 +240,8 @@ mod tests {
             "head.hbs",
             "redirect.hbs",
             "header.hbs",
+            "toc.js.hbs",
+            "toc.html.hbs",
             "favicon.png",
             "favicon.svg",
             "css/chrome.css",
@@ -263,6 +273,8 @@ mod tests {
             head: Vec::new(),
             redirect: Vec::new(),
             header: Vec::new(),
+            toc_js: Vec::new(),
+            toc_html: Vec::new(),
             chrome_css: Vec::new(),
             general_css: Vec::new(),
             print_css: Vec::new(),

src/theme/toc.html.hbs

@@ -0,0 +1,43 @@
+<!DOCTYPE HTML>
+<html lang="{{ language }}" class="{{ default_theme }}" dir="{{ text_direction }}">
+    <head>
+        <!-- sidebar iframe generated using mdBook
+
+        This is a frame, and not included directly in the page, to control the total size of the
+        book. The TOC contains an entry for each page, so if each page includes a copy of the TOC,
+        the total size of the page becomes O(n**2).
+
+        The frame is only used as a fallback when JS is turned off. When it's on, the sidebar is
+        instead added to the main page by `toc.js` instead. The JavaScript mode is better
+        because, when running in a `file:///` URL, the iframed page would not be Same-Origin as
+        the rest of the page, so the sidebar and the main page theme would fall out of sync.
+        -->
+        <meta charset="UTF-8">
+        <meta name="robots" content="noindex">
+        {{#if base_url}}
+        <base href="{{ base_url }}">
+        {{/if}}
+        <!-- Custom HTML head -->
+        {{> head}}
+        <meta name="viewport" content="width=device-width, initial-scale=1">
+        <meta name="theme-color" content="#ffffff">
+        <link rel="stylesheet" href="{{ path_to_root }}css/variables.css">
+        <link rel="stylesheet" href="{{ path_to_root }}css/general.css">
+        <link rel="stylesheet" href="{{ path_to_root }}css/chrome.css">
+        {{#if print_enable}}
+        <link rel="stylesheet" href="{{ path_to_root }}css/print.css" media="print">
+        {{/if}}
+        <!-- Fonts -->
+        <link rel="stylesheet" href="{{ path_to_root }}FontAwesome/css/font-awesome.css">
+        {{#if copy_fonts}}
+        <link rel="stylesheet" href="{{ path_to_root }}fonts/fonts.css">
+        {{/if}}
+        <!-- Custom theme stylesheets -->
+        {{#each additional_css}}
+        <link rel="stylesheet" href="{{ ../path_to_root }}{{ this }}">
+        {{/each}}
+    </head>
+    <body class="sidebar-iframe-inner">
+        {{#toc}}{{/toc}}
+    </body>
+</html>

src/theme/toc.js.hbs

@@ -0,0 +1,54 @@
+// Populate the sidebar
+//
+// This is a script, and not included directly in the page, to control the total size of the book.
+// The TOC contains an entry for each page, so if each page includes a copy of the TOC,
+// the total size of the page becomes O(n**2).
+var sidebarScrollbox = document.querySelector("#sidebar .sidebar-scrollbox");
+sidebarScrollbox.innerHTML = '{{#toc}}{{/toc}}';
+(function() {
+    let current_page = document.location.href.toString();
+    if (current_page.endsWith("/")) {
+        current_page += "index.html";
+    }
+    var links = sidebarScrollbox.querySelectorAll("a");
+    var l = links.length;
+    for (var i = 0; i < l; ++i) {
+        var link = links[i];
+        var href = link.getAttribute("href");
+        if (href && !href.startsWith("#") && !/^(?:[a-z+]+:)?\/\//.test(href)) {
+            link.href = path_to_root + href;
+        }
+        // The "index" page is supposed to alias the first chapter in the book.
+        if (link.href === current_page || (i === 0 && path_to_root === "" && current_page.endsWith("/index.html"))) {
+            link.classList.add("active");
+            var parent = link.parentElement;
+            while (parent) {
+                if (parent.tagName === "LI" && parent.previousElementSibling) {
+                    if (parent.previousElementSibling.classList.contains("chapter-item")) {
+                        parent.previousElementSibling.classList.add("expanded");
+                    }
+                }
+                parent = parent.parentElement;
+            }
+        }
+    }
+})();
+
+// Track and set sidebar scroll position
+sidebarScrollbox.addEventListener('click', function(e) {
+    if (e.target.tagName === 'A') {
+        sessionStorage.setItem('sidebar-scroll', sidebarScrollbox.scrollTop);
+    }
+}, { passive: true });
+var sidebarScrollTop = sessionStorage.getItem('sidebar-scroll');
+sessionStorage.removeItem('sidebar-scroll');
+if (sidebarScrollTop) {
+    // preserve sidebar scroll position when navigating via links within sidebar
+    sidebarScrollbox.scrollTop = sidebarScrollTop;
+} else {
+    // scroll sidebar to current active section when navigating via "next/previous chapter" buttons
+    var activeSection = document.querySelector('#sidebar .active');
+    if (activeSection) {
+        activeSection.scrollIntoView({ block: 'center' });
+    }
+}