From 34dc0a88358e37c45aee46deceb905579bd5d057 Mon Sep 17 00:00:00 2001
From: Michael Howell <michael@notriddle.com>
Date: Tue, 16 Jul 2024 12:23:26 -0700
Subject: [PATCH] Make the sidebar work without JS

Uses an iframe instead. The downside of iframes comes from them
not necessarily being same-origin as the main page (particularly
with `file:///` URLs), which can cause themes to fall out of sync,
but that's not a problem here since themes don't work without JS
anyway.
---
 src/renderer/html_handlebars/hbs_renderer.rs | 10 +++--
 src/theme/css/chrome.css                     | 16 ++++++++
 src/theme/index.hbs                          |  3 ++
 src/theme/mod.rs                             | 16 +++++---
 src/theme/toc.html.hbs                       | 43 ++++++++++++++++++++
 5 files changed, 80 insertions(+), 8 deletions(-)
 create mode 100644 src/theme/toc.html.hbs

diff --git a/src/renderer/html_handlebars/hbs_renderer.rs b/src/renderer/html_handlebars/hbs_renderer.rs
index a591e86ffe..64bfd85cc0 100644
--- a/src/renderer/html_handlebars/hbs_renderer.rs
+++ b/src/renderer/html_handlebars/hbs_renderer.rs
@@ -529,7 +529,8 @@ impl Renderer for HtmlHandlebars {
         handlebars.register_partial("header", String::from_utf8(theme.header.clone())?)?;
 
         debug!("Register the toc handlebars template");
-        handlebars.register_template_string("toc", String::from_utf8(theme.toc.clone())?)?;
+        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);
@@ -586,11 +587,14 @@ impl Renderer for HtmlHandlebars {
             debug!("Creating print.html ✓");
         }
 
-        debug!("Render toc.js");
+        debug!("Render toc");
         {
-            let rendered_toc = handlebars.render("toc", &data)?;
+            let rendered_toc = handlebars.render("toc_js", &data)?;
             utils::fs::write_file(destination, "toc.js", rendered_toc.as_bytes())?;
             debug!("Creating toc.js ✓");
+            let rendered_toc = handlebars.render("toc_html", &data)?;
+            utils::fs::write_file(destination, "toc.html", rendered_toc.as_bytes())?;
+            debug!("Creating toc.html ✓");
         }
 
         debug!("Copy static files");
diff --git a/src/theme/css/chrome.css b/src/theme/css/chrome.css
index 83b7969bce..e62056b053 100644
--- a/src/theme/css/chrome.css
+++ b/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;
diff --git a/src/theme/index.hbs b/src/theme/index.hbs
index fb6c10b2b8..97f59a1325 100644
--- a/src/theme/index.hbs
+++ b/src/theme/index.hbs
@@ -111,6 +111,9 @@
         <nav id="sidebar" class="sidebar" aria-label="Table of contents">
             <!-- 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>
diff --git a/src/theme/mod.rs b/src/theme/mod.rs
index bbaeaa4442..b173bd4a19 100644
--- a/src/theme/mod.rs
+++ b/src/theme/mod.rs
@@ -17,7 +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: &[u8] = include_bytes!("toc.js.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");
@@ -51,7 +52,8 @@ pub struct Theme {
     pub head: Vec<u8>,
     pub redirect: Vec<u8>,
     pub header: Vec<u8>,
-    pub toc: 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>,
@@ -87,7 +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),
+                (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),
@@ -177,7 +180,8 @@ impl Default for Theme {
             head: HEAD.to_owned(),
             redirect: REDIRECT.to_owned(),
             header: HEADER.to_owned(),
-            toc: TOC.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(),
@@ -237,6 +241,7 @@ mod tests {
             "redirect.hbs",
             "header.hbs",
             "toc.js.hbs",
+            "toc.html.hbs",
             "favicon.png",
             "favicon.svg",
             "css/chrome.css",
@@ -268,7 +273,8 @@ mod tests {
             head: Vec::new(),
             redirect: Vec::new(),
             header: Vec::new(),
-            toc: Vec::new(),
+            toc_js: Vec::new(),
+            toc_html: Vec::new(),
             chrome_css: Vec::new(),
             general_css: Vec::new(),
             print_css: Vec::new(),
diff --git a/src/theme/toc.html.hbs b/src/theme/toc.html.hbs
new file mode 100644
index 0000000000..f8fca87353
--- /dev/null
+++ b/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>