rust-lang · Dylan-DPC-zz · Oct 19, 2019 · Sep 15, 2019 · Sep 15, 2019 · Sep 15, 2019
diff --git a/book-example/src/format/config.md b/book-example/src/format/config.md
@@ -166,13 +166,21 @@ The following configuration options are available:
 - **no-section-label:** mdBook by defaults adds section label in table of
   contents column. For example, "1.", "2.1". Set this option to true to disable
   those labels. Defaults to `false`.
+- **fold:** A subtable for configuring sidebar section-folding behavior.
 - **playpen:** A subtable for configuring various playpen settings.
 - **search:** A subtable for configuring the in-browser search functionality.
   mdBook must be compiled with the `search` feature enabled (on by default).
 - **git-repository-url:**  A url to the git repository for the book. If provided
   an icon link will be output in the menu bar of the book.
 - **git-repository-icon:** The FontAwesome icon class to use for the git
   repository link. Defaults to `fa-github`.
+
+Available configuration options for the `[output.html.fold]` table:
+
+- **enable:** Enable section-folding. When off, all folds are open.
+  Defaults to `false`.
+- **level:** The higher the more folded regions are open. When level is 0, all
+  folds are closed. Defaults to `0`.
 
 Available configuration options for the `[output.html.playpen]` table:
 
@@ -225,6 +233,10 @@ no-section-label = false
 git-repository-url = "https://github.com/rust-lang-nursery/mdBook"
 git-repository-icon = "fa-github"
 
+[output.html.fold]
+enable = false
+level = 0
+
 [output.html.playpen]
 editable = false
 copy-js = true

diff --git a/src/config.rs b/src/config.rs
@@ -431,16 +431,10 @@ pub struct HtmlConfig {
     /// Additional JS scripts to include at the bottom of the rendered page's
     /// `<body>`.
     pub additional_js: Vec<PathBuf>,
+    /// Fold settings.
+    pub fold: Fold,
     /// Playpen settings.
     pub playpen: Playpen,
-    /// This is used as a bit of a workaround for the `mdbook serve` command.
-    /// Basically, because you set the websocket port from the command line, the
-    /// `mdbook serve` command needs a way to let the HTML renderer know where
-    /// to point livereloading at, if it has been enabled.
-    ///
-    /// This config item *should not be edited* by the end user.
-    #[doc(hidden)]
-    pub livereload_url: Option<String>,
     /// Don't render section labels.
     pub no_section_label: bool,
     /// Search settings. If `None`, the default will be used.
@@ -450,6 +444,14 @@ pub struct HtmlConfig {
     /// FontAwesome icon class to use for the Git repository link.
     /// Defaults to `fa-github` if `None`.
     pub git_repository_icon: Option<String>,
+    /// This is used as a bit of a workaround for the `mdbook serve` command.
+    /// Basically, because you set the websocket port from the command line, the
+    /// `mdbook serve` command needs a way to let the HTML renderer know where
+    /// to point livereloading at, if it has been enabled.
+    ///
+    /// This config item *should not be edited* by the end user.
+    #[doc(hidden)]
+    pub livereload_url: Option<String>,
 }
 
 impl HtmlConfig {
@@ -463,6 +465,18 @@ impl HtmlConfig {
     }
 }
 
+/// Configuration for how to fold chapters of sidebar.
+#[derive(Default, Debug, Clone, PartialEq, Serialize, Deserialize)]
+#[serde(default, rename_all = "kebab-case")]
+pub struct Fold {
+    /// When off, all folds are open. Default: `false`.
+    pub enable: bool,
+    /// The higher the more folded regions are open. When level is 0, all folds
+    /// are closed.
+    /// Default: `0`.
+    pub level: u8,
+}
+
 /// Configuration for tweaking how the the HTML renderer handles the playpen.
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 #[serde(default, rename_all = "kebab-case")]

diff --git a/src/renderer/html_handlebars/hbs_renderer.rs b/src/renderer/html_handlebars/hbs_renderer.rs
@@ -71,6 +71,10 @@ impl HtmlHandlebars {
                 "path_to_root".to_owned(),
                 json!(utils::fs::path_to_root(&ch.path)),
             );
+            if let Some(ref section) = ch.number {
+                ctx.data
+                    .insert("section".to_owned(), json!(section.to_string()));
+            }
 
             // Render the handlebars template with the data
             debug!("Render template");
@@ -444,6 +448,9 @@ fn make_data(
         data.insert("playpen_js".to_owned(), json!(true));
     }
 
+    data.insert("fold_enable".to_owned(), json!((html_config.fold.enable)));
+    data.insert("fold_level".to_owned(), json!((html_config.fold.level)));
+
     let search = html_config.search.clone();
     if cfg!(feature = "search") {
         let search = search.unwrap_or_default();
@@ -463,6 +470,7 @@ fn make_data(
     if let Some(ref git_repository_url) = html_config.git_repository_url {
         data.insert("git_repository_url".to_owned(), json!(git_repository_url));
     }
+
     let git_repository_icon = match html_config.git_repository_icon {
         Some(ref git_repository_icon) => git_repository_icon,
         None => "fa-github",
@@ -481,6 +489,11 @@ fn make_data(
                     chapter.insert("section".to_owned(), json!(section.to_string()));
                 }
 
+                chapter.insert(
+                    "has_sub_items".to_owned(),
+                    json!((!ch.sub_items.is_empty()).to_string()),
+                );
+
                 chapter.insert("name".to_owned(), json!(ch.name));
                 let path = ch
                     .path

diff --git a/src/renderer/html_handlebars/helpers/toc.rs b/src/renderer/html_handlebars/helpers/toc.rs
@@ -28,13 +28,36 @@ impl HelperDef for RenderToc {
             serde_json::value::from_value::<Vec<BTreeMap<String, String>>>(c.as_json().clone())
                 .map_err(|_| RenderError::new("Could not decode the JSON data"))
         })?;
-        let current = rc
+        let current_path = rc
             .evaluate(ctx, "@root/path")?
             .as_json()
             .as_str()
-            .ok_or_else(|| RenderError::new("Type error for `path`, string expected"))?
+            .ok_or(RenderError::new("Type error for `path`, string expected"))?
             .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")?
+            .as_json()
+            .as_bool()
+            .ok_or(RenderError::new(
+                "Type error for `fold_enable`, bool expected",
+            ))?;
+
+        let fold_level = rc
+            .evaluate(ctx, "@root/fold_level")?
+            .as_json()
+            .as_u64()
+            .ok_or(RenderError::new(
+                "Type error for `fold_level`, u64 expected",
+            ))?;
+
         out.write("<ol class=\"chapter\">")?;
 
         let mut current_level = 1;
@@ -46,10 +69,23 @@ impl HelperDef for RenderToc {
                 continue;
             }
 
-            let level = if let Some(s) = item.get("section") {
-                s.matches('.').count()
+            let (section, level) = if let Some(s) = item.get("section") {
+                (s.as_str(), s.matches('.').count())
             } else {
-                1
+                ("", 1)
+            };
+
+            let is_expanded = {
+                if !fold_enable {
+                    // Disable fold. Expand all chapters.
+                    true
+                } else if !section.is_empty() && current_section.starts_with(section) {
+                    // The section is ancestor or the current section itself.
+                    true
+                } else {
+                    // Levels that are larger than this would be folded.
+                    level - 1 < fold_level as usize
+                }
             };
 
             if level > current_level {
@@ -58,20 +94,16 @@ impl HelperDef for RenderToc {
                     out.write("<ol class=\"section\">")?;
                     current_level += 1;
                 }
-                out.write("<li>")?;
+                write_li_open_tag(out, is_expanded, false)?;
             } else if level < current_level {
                 while level < current_level {
                     out.write("</ol>")?;
                     out.write("</li>")?;
                     current_level -= 1;
                 }
-                out.write("<li>")?;
+                write_li_open_tag(out, is_expanded, false)?;
             } else {
-                out.write("<li")?;
-                if item.get("section").is_none() {
-                    out.write(" class=\"affix\"")?;
-                }
-                out.write(">")?;
+                write_li_open_tag(out, is_expanded, item.get("section").is_none())?;
             }
 
             // Link
@@ -87,11 +119,11 @@ impl HelperDef for RenderToc {
                         .replace("\\", "/");
 
                     // Add link
-                    out.write(&utils::fs::path_to_root(&current))?;
+                    out.write(&utils::fs::path_to_root(&current_path))?;
                     out.write(&tmp)?;
                     out.write("\"")?;
 
-                    if path == &current {
+                    if path == &current_path {
                         out.write(" class=\"active\"")?;
                     }
 
@@ -134,6 +166,13 @@ impl HelperDef for RenderToc {
                 out.write("</a>")?;
             }
 
+            // Render expand/collapse toggle
+            if let Some(flag) = item.get("has_sub_items") {
+                let has_sub_items = flag.parse::<bool>().unwrap_or_default();
+                if fold_enable && has_sub_items {
+                    out.write("<a class=\"toggle\"><div>❱</div></a>")?;
+                }
+            }
             out.write("</li>")?;
         }
         while current_level > 1 {
@@ -146,3 +185,19 @@ impl HelperDef for RenderToc {
         Ok(())
     }
 }
+
+fn write_li_open_tag(
+    out: &mut dyn Output,
+    is_expanded: bool,
+    is_affix: bool,
+) -> Result<(), std::io::Error> {
+    let mut li = String::from("<li class=\"");
+    if is_expanded {
+        li.push_str("expanded ");
+    }
+    if is_affix {
+        li.push_str("affix ");
+    }
+    li.push_str("\">");
+    out.write(&li)
+}
diff --git a/src/theme/book.js b/src/theme/book.js
@@ -451,6 +451,17 @@ function playpen_text(playpen) {
         try { localStorage.setItem('mdbook-sidebar', 'visible'); } catch (e) { }
     }
 
+
+    var sidebarAnchorToggles = document.querySelectorAll('#sidebar a.toggle');
+
+    function toggleSection(ev) {
+        ev.currentTarget.parentElement.classList.toggle('expanded');
+    }
+
+    Array.from(sidebarAnchorToggles).forEach(function (el) {
+        el.addEventListener('click', toggleSection);
+    });
+
     function hideSidebar() {
         html.classList.remove('sidebar-visible')
         html.classList.add('sidebar-hidden');

diff --git a/src/theme/css/chrome.css b/src/theme/css/chrome.css
@@ -376,7 +376,13 @@ ul#searchresults span.teaser em {
     padding-left: 0;
     line-height: 2.2em;
 }
+
+.chapter ol {
+    width: 100%;
+}
+
 .chapter li {
+    display: flex;
     color: var(--sidebar-non-existant);
 }
 .chapter li a {
@@ -390,10 +396,32 @@ ul#searchresults span.teaser em {
     color: var(--sidebar-active);
 }
 
-.chapter li .active {
+.chapter li a.active {
     color: var(--sidebar-active);
 }
 
+.chapter li > a.toggle {
+    cursor: pointer;
+    display: block;
+    margin-left: auto;
+    padding: 0 10px;
+    user-select: none;
+    opacity: 0.68;
+}
+
+.chapter li > a.toggle div {
+    transition: transform 0.5s;
+}
+
+/* collapse the section */
+.chapter li:not(.expanded) + li > ol {
+    display: none;
+}
+
+.chapter li.expanded > a.toggle div {
+    transform: rotate(90deg);
+}
+
 .spacer {
     width: 100%;
     height: 3px;

diff --git a/tests/rendered_output.rs b/tests/rendered_output.rs
@@ -235,7 +235,12 @@ fn check_second_toc_level() {
     let mut should_be = Vec::from(TOC_SECOND_LEVEL);
     should_be.sort();
 
-    let pred = descendants!(Class("chapter"), Name("li"), Name("li"), Name("a"));
+    let pred = descendants!(
+        Class("chapter"),
+        Name("li"),
+        Name("li"),
+        Name("a").and(Class("toggle").not())
+    );
 
     let mut children_of_children: Vec<_> = doc
         .find(pred)
@@ -254,7 +259,11 @@ fn check_first_toc_level() {
     should_be.extend(TOC_SECOND_LEVEL);
     should_be.sort();
 
-    let pred = descendants!(Class("chapter"), Name("li"), Name("a"));
+    let pred = descendants!(
+        Class("chapter"),
+        Name("li"),
+        Name("a").and(Class("toggle").not())
+    );
 
     let mut children: Vec<_> = doc
         .find(pred)