Fix up "index page" functionality

src/renderer/html_handlebars/hbs_renderer.rs

@@ -116,7 +116,7 @@ impl HtmlHandlebars {
         if ctx.is_index {
             ctx.data.insert("path".to_owned(), json!("index.md"));
             ctx.data.insert("path_to_root".to_owned(), json!(""));
-            ctx.data.insert("is_index".to_owned(), json!("true"));
+            ctx.data.insert("is_index".to_owned(), json!(true));
             let rendered_index = ctx.handlebars.render("index", &ctx.data)?;
             let rendered_index =
                 self.post_process(rendered_index, &ctx.html_config.playground, ctx.edition);
@@ -540,7 +540,8 @@ impl Renderer for HtmlHandlebars {
                 chapter_titles: &ctx.chapter_titles,
             };
             self.render_item(item, ctx, &mut print_content)?;
-            is_index = false;
+            // Only the first non-draft chapter item should be treated as the "index"
+            is_index &= !matches!(item, BookItem::Chapter(ch) if !ch.is_draft_chapter());
         }
 
         // Render 404 page

src/renderer/html_handlebars/helpers/toc.rs

@@ -57,6 +57,11 @@ impl HelperDef for RenderToc {
         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 {
             // Spacer
@@ -130,7 +135,8 @@ impl HelperDef for RenderToc {
                 out.write(&tmp)?;
                 out.write("\"")?;
 
-                if path == &current_path {
+                if path == &current_path || is_first_chapter {
+                    is_first_chapter = false;
                     out.write(" class=\"active\"")?;
                 }
 

tests/dummy_book/index_html_test/SUMMARY.md

@@ -0,0 +1,11 @@
+# Summary
+
+---
+
+- [None of these should be treated as the "index chapter"]()
+
+# Part 1
+
+- [Not this either]()
+- [Chapter 1](./chapter_1.md)
+- [And not this]()

tests/dummy_book/index_html_test/chapter_1.md

@@ -0,0 +1 @@
+# Chapter 1

tests/rendered_output.rs

@@ -467,6 +467,21 @@ fn by_default_mdbook_use_index_preprocessor_to_convert_readme_to_index() {
     assert_doesnt_contain_strings(&second_index, &unexpected_strings);
 }
 
+#[test]
+fn first_chapter_is_copied_as_index_even_if_not_first_elem() {
+    let temp = DummyBook::new().build().unwrap();
+    let mut cfg = Config::default();
+    cfg.set("book.src", "index_html_test")
+        .expect("Couldn't set config.book.src to \"index_html_test\"");
+    let md = MDBook::load_with_config(temp.path(), cfg).unwrap();
+    md.build().unwrap();
+
+    let root = temp.path().join("book");
+    let chapter = fs::read_to_string(root.join("chapter_1.html")).expect("read chapter 1");
+    let index = fs::read_to_string(root.join("index.html")).expect("read index");
+    pretty_assertions::assert_eq!(chapter, index);
+}
+
 #[test]
 fn theme_dir_overrides_work_correctly() {
     let book_dir = dummy_book::new_copy_of_example_book().unwrap();