Rollup merge of #25551 - cllns:add-active-class-to-rustbook-toc, r=alexcrichton

Currently the table of contents for `rustbook` doesn't signify which page you are on.

This PR adds an 'active' class to the link for the current page, and defines the CSS rule for that class to make the link underlined and bold.

Not sure about two things:
1) Is `current_page` is a good name for the function parameter? At first I thought `current_item` would be good, but then in the `walk_item` function, you'd have `item` and `current_item`.

2) For the CSS, is both bold and underline too much? At first I had it just be underlined, but that's also how the links look when they're hovered over.

Author: Manishearth

src/rustbook/build.rs

@@ -37,27 +37,34 @@ pub fn parse_cmd(name: &str) -> Option<Box<Subcommand>> {
     }
 }
 
-fn write_toc(book: &Book, path_to_root: &Path, out: &mut Write) -> io::Result<()> {
+fn write_toc(book: &Book, current_page: &BookItem, out: &mut Write) -> io::Result<()> {
     fn walk_items(items: &[BookItem],
                   section: &str,
-                  path_to_root: &Path,
+                  current_page: &BookItem,
                   out: &mut Write) -> io::Result<()> {
         for (i, item) in items.iter().enumerate() {
-            try!(walk_item(item, &format!("{}{}.", section, i + 1)[..], path_to_root, out));
+            try!(walk_item(item, &format!("{}{}.", section, i + 1)[..], current_page, out));
         }
         Ok(())
     }
     fn walk_item(item: &BookItem,
                  section: &str,
-                 path_to_root: &Path,
+                 current_page: &BookItem,
                  out: &mut Write) -> io::Result<()> {
-        try!(writeln!(out, "<li><a href='{}'><b>{}</b> {}</a>",
-                 path_to_root.join(&item.path.with_extension("html")).display(),
+        let class_string = if item.path == current_page.path {
+          "class='active'"
+        } else {
+        ""
+        };
+
+        try!(writeln!(out, "<li><a {} href='{}'><b>{}</b> {}</a>",
+                 class_string,
+                 item.path_to_root.join(&item.path.with_extension("html")).display(),
                  section,
                  item.title));
         if !item.children.is_empty() {
             try!(writeln!(out, "<ul class='section'>"));
-            let _ = walk_items(&item.children[..], section, path_to_root, out);
+            let _ = walk_items(&item.children[..], section, current_page, out);
             try!(writeln!(out, "</ul>"));
         }
         try!(writeln!(out, "</li>"));
@@ -67,7 +74,7 @@ fn write_toc(book: &Book, path_to_root: &Path, out: &mut Write) -> io::Result<()
 
     try!(writeln!(out, "<div id='toc' class='mobile-hidden'>"));
     try!(writeln!(out, "<ul class='chapter'>"));
-    try!(walk_items(&book.chapters[..], "", path_to_root, out));
+    try!(walk_items(&book.chapters[..], "", &current_page, out));
     try!(writeln!(out, "</ul>"));
     try!(writeln!(out, "</div>"));
 
@@ -115,7 +122,7 @@ fn render(book: &Book, tgt: &Path) -> CliResult<()> {
                   <span class="bar"></span>
                 </button>
               </div>"#));
-            let _ = write_toc(book, &item.path_to_root, &mut toc);
+            let _ = write_toc(book, &item, &mut toc);
             try!(writeln!(&mut toc, "<div id='page-wrapper'>"));
             try!(writeln!(&mut toc, "<div id='page'>"));
         }

src/rustbook/css.rs

@@ -97,6 +97,11 @@ body {
     color: #000000;
 }
 
+.chapter li a.active {
+    text-decoration: underline;
+    font-weight: bold;
+}
+
 #toggle-nav {
     height: 20px;
     width:  30px;