From 897605a111d14dae274f5f7006ab9477633ed0e3 Mon Sep 17 00:00:00 2001
From: Maciej Sopylo <me@klh.io>
Date: Tue, 18 Nov 2025 21:50:02 +0100
Subject: [PATCH] Fix built html saved outside build directory

The fix reconstructs the directory tree inside the build path so links
still work the same.
---
 .../src/html_handlebars/hbs_renderer.rs       | 27 +++++++++++++++++--
 tests/testsuite/rendering.rs                  | 15 +++++++++++
 .../parent/src/SUMMARY.md                     |  1 +
 .../parent/test.md                            |  1 +
 4 files changed, 42 insertions(+), 2 deletions(-)
 create mode 100644 tests/testsuite/rendering/including_files_from_parent_directories_works/parent/src/SUMMARY.md
 create mode 100644 tests/testsuite/rendering/including_files_from_parent_directories_works/parent/test.md

diff --git a/crates/mdbook-html/src/html_handlebars/hbs_renderer.rs b/crates/mdbook-html/src/html_handlebars/hbs_renderer.rs
index 8edac3cace..27e3952ca9 100644
--- a/crates/mdbook-html/src/html_handlebars/hbs_renderer.rs
+++ b/crates/mdbook-html/src/html_handlebars/hbs_renderer.rs
@@ -12,7 +12,8 @@ use mdbook_core::utils::fs;
 use mdbook_renderer::{RenderContext, Renderer};
 use serde_json::json;
 use std::collections::{BTreeMap, HashMap};
-use std::path::{Path, PathBuf};
+use std::iter::{repeat, zip};
+use std::path::{Component, Path, PathBuf};
 use tracing::error;
 use tracing::{debug, info, trace, warn};
 
@@ -119,8 +120,30 @@ impl HtmlHandlebars {
         debug!("Render template");
         let rendered = ctx.handlebars.render("index", &ctx.data)?;
 
+        // Calculate an output path that's contained in the specified destination
+        // This is required to be able to reference files in the parent directory
+        // without putting the HTML files there
+        let out_path = ctx.destination.join(
+            &filepath
+                .parent()
+                .context("filepath points to a directory")?,
+        );
+        fs::create_dir_all(&out_path).context("could not create output directories")?;
+        let fixed_path: PathBuf = zip(
+            ctx.destination
+                .components()
+                // padding destination because it's always shorter
+                .chain(repeat(Component::CurDir)),
+            std::fs::canonicalize(&out_path)?.components(),
+        )
+        .skip_while(|(out, canonicalized)| out == canonicalized)
+        .map(|(_, canonicalized)| canonicalized)
+        .collect();
+        let out_path = ctx
+            .destination
+            .join(fixed_path)
+            .join(filepath.file_name().context("filepath points to parent")?);
         // Write to file
-        let out_path = ctx.destination.join(filepath);
         fs::write(&out_path, rendered)?;
 
         if prev_ch.is_none() {
diff --git a/tests/testsuite/rendering.rs b/tests/testsuite/rendering.rs
index 421aa5d45c..08855d4c31 100644
--- a/tests/testsuite/rendering.rs
+++ b/tests/testsuite/rendering.rs
@@ -304,3 +304,18 @@ HTML tags must be closed before exiting a markdown element.
             str![[r##"<h3 id="option"><a class="header" href="#option">Option<t></t></a></h3>"##]],
         );
 }
+
+#[test]
+fn including_files_from_parent_directories_works() {
+    let mut test =
+        BookTest::from_dir("rendering/including_files_from_parent_directories_works/parent");
+    test.check_main_file(
+        "book/index.html",
+        str![[r##"<h1 id="test"><a class="header" href="#test">Test!</a></h1>"##]],
+    );
+
+    assert!(
+        !std::fs::exists(test.dir.join("../test.html")).unwrap(),
+        "test.html was rendered outside build directory"
+    );
+}
diff --git a/tests/testsuite/rendering/including_files_from_parent_directories_works/parent/src/SUMMARY.md b/tests/testsuite/rendering/including_files_from_parent_directories_works/parent/src/SUMMARY.md
new file mode 100644
index 0000000000..9427acaf9a
--- /dev/null
+++ b/tests/testsuite/rendering/including_files_from_parent_directories_works/parent/src/SUMMARY.md
@@ -0,0 +1 @@
+[test](../test.md)
diff --git a/tests/testsuite/rendering/including_files_from_parent_directories_works/parent/test.md b/tests/testsuite/rendering/including_files_from_parent_directories_works/parent/test.md
new file mode 100644
index 0000000000..ef93b2403f
--- /dev/null
+++ b/tests/testsuite/rendering/including_files_from_parent_directories_works/parent/test.md
@@ -0,0 +1 @@
+# Test!