From 1f9c86967e582d96b5e0e75bbbf40706acbcced5 Mon Sep 17 00:00:00 2001
From: Travis Cross <tc@traviscross.com>
Date: Thu, 4 Sep 2025 10:34:50 +0000
Subject: [PATCH] Enable folding of chapter listing in navigation sidebar

We have many chapters and subchapters.  Listing all of the subchapters
in the navigation sidebar by default can make it difficult to see the
high level structure of the Reference and can inhibit rapid navigation
based on that hierarchical structure.

Fortunately, mdbook has an option to fold the chapter listing.  This
causes only the top-level chapters to be shown by default while giving
the user the ability to unfold individual chapters.  Let's turn on
that option.
---
 book.toml | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/book.toml b/book.toml
index c2cd24d0b2..bf8f63ef29 100644
--- a/book.toml
+++ b/book.toml
@@ -10,6 +10,10 @@ git-repository-url = "https://github.com/rust-lang/reference/"
 edit-url-template = "https://github.com/rust-lang/reference/edit/master/{path}"
 smart-punctuation = true
 
+[output.html.fold]
+enable = true
+level = 0
+
 [output.html.search.chapter]
 "test-summary.md" = { enable = false }
 "grammar.md" = { enable = false }