From 59343b525df32141bdd5c6ac36ec3137b9f79129 Mon Sep 17 00:00:00 2001
From: Eric Huss <eric@huss.org>
Date: Thu, 30 Oct 2025 17:48:03 -0700
Subject: [PATCH 1/2] Add test for print relative for page that doesn't exist

An example where this can happen is a link to a page that was renamed
and redirected, or just a normal HTML file.
---
 tests/testsuite/print/relative_links/expected/print.html  | 4 ++++
 tests/testsuite/print/relative_links/src/second/nested.md | 5 +++++
 2 files changed, 9 insertions(+)

diff --git a/tests/testsuite/print/relative_links/expected/print.html b/tests/testsuite/print/relative_links/expected/print.html
index b1e181b7be..2dfbff2059 100644
--- a/tests/testsuite/print/relative_links/expected/print.html
+++ b/tests/testsuite/print/relative_links/expected/print.html
@@ -9,6 +9,10 @@ <h1 id="testing-relative-links-for-the-print-page"><a class="header" href="#test
 <p>A <a href="#some-section">fragment link</a> should work.</p>
 <p>Link <a href="../std/foo/bar.html">outside</a>.</p>
 <p>Link <a href="../std/foo/bar.html#panic">outside with anchor</a>.</p>
+<p>Link <a href="../first/alpha/beta.html">inside but doesn’t exist</a>.
+Link <a href="#anchor">inside but doesn’t exist with anchor</a>.
+Link <a href="../first/alpha/gamma.html">inside to html</a>.
+Link <a href="#anchor">inside to html with anchor</a>.</p>
 <p><img src="images/picture.png" alt="Some image"></p>
 <p><a href="#first-nested">HTML Link</a></p>
 <img src="images/picture.png" alt="raw html">
diff --git a/tests/testsuite/print/relative_links/src/second/nested.md b/tests/testsuite/print/relative_links/src/second/nested.md
index d888620391..443f00a22a 100644
--- a/tests/testsuite/print/relative_links/src/second/nested.md
+++ b/tests/testsuite/print/relative_links/src/second/nested.md
@@ -11,6 +11,11 @@ Link [outside](../../std/foo/bar.html).
 
 Link [outside with anchor](../../std/foo/bar.html#panic).
 
+Link [inside but doesn't exist](../first/alpha/beta.md).
+Link [inside but doesn't exist with anchor](../first/alpha/beta.md#anchor).
+Link [inside to html](../first/alpha/gamma.html).
+Link [inside to html with anchor](../first/alpha/gamma.html#anchor).
+
 ![Some image](../images/picture.png)
 
 <a href="../first/nested.md">HTML Link</a>

From 005f4d648aedfa3e3d42b7c13ce0694d386f4b78 Mon Sep 17 00:00:00 2001
From: Eric Huss <eric@huss.org>
Date: Thu, 30 Oct 2025 18:37:12 -0700
Subject: [PATCH 2/2] Fix print page links for internal links to non-chapters

This fixes links on the print page that go to an internal destination
that is not a chapter. The path would have the wrong relative
destination, and would be broken. The logic for detecting this was
incorrectly only checking if a link went outside the book, or didn't
have an html extension. This doesn't work for links to HTML files that
are inside the book, but not one of the chapters.
---
 crates/mdbook-html/src/html/print.rs          | 27 ++++++++++---------
 .../print/relative_links/expected/print.html  |  8 +++---
 2 files changed, 18 insertions(+), 17 deletions(-)

diff --git a/crates/mdbook-html/src/html/print.rs b/crates/mdbook-html/src/html/print.rs
index 3688a979c3..e325396fd9 100644
--- a/crates/mdbook-html/src/html/print.rs
+++ b/crates/mdbook-html/src/html/print.rs
@@ -9,7 +9,7 @@ use crate::html::{ChapterTree, Element, serialize};
 use crate::utils::{ToUrlPath, id_from_content, normalize_path, unique_id};
 use mdbook_core::static_regex;
 use std::collections::{HashMap, HashSet};
-use std::path::{Component, PathBuf};
+use std::path::PathBuf;
 
 /// Takes all the chapter trees, modifies them to be suitable to render for
 /// the print page, and returns an string of all the chapters rendered to a
@@ -166,13 +166,9 @@ fn rewrite_links(
                 {
                     lookup_key.pop();
                     lookup_key.push(href_path);
-                    let normalized = normalize_path(&lookup_key);
-                    // If this points outside of the book, don't modify it.
-                    let is_outside = matches!(
-                        normalized.components().next(),
-                        Some(Component::ParentDir | Component::RootDir)
-                    );
-                    if is_outside || !href_path.ends_with(".html") {
+                    lookup_key = normalize_path(&lookup_key);
+                    let is_a_chapter = path_to_root_id.contains_key(&lookup_key);
+                    if !is_a_chapter {
                         // Make the link relative to the print page location.
                         let mut rel_path = normalize_path(&base.join(href_path)).to_url_path();
                         if let Some(anchor) = caps.name("anchor") {
@@ -184,10 +180,7 @@ fn rewrite_links(
                     }
                 }
 
-                let lookup_key = normalize_path(&lookup_key);
-
-                let anchor = caps.name("anchor");
-                let id = match anchor {
+                let id = match caps.name("anchor") {
                     Some(anchor_id) => {
                         let anchor_id = anchor_id.as_str().to_string();
                         match id_remap.get(&lookup_key) {
@@ -204,7 +197,15 @@ fn rewrite_links(
                     }
                     None => match path_to_root_id.get(&lookup_key) {
                         Some(id) => id.to_string(),
-                        None => continue,
+                        None => {
+                            // This should be guaranteed that either the
+                            // chapter itself is in the map (for anchor-only
+                            // links), or the is_a_chapter check above.
+                            panic!(
+                                "internal error: expected `{lookup_key:?}` to be in \
+                                 root map (chapter path is `{html_path:?}`)"
+                            );
+                        }
                     },
                 };
                 el.insert_attr(attr, format!("#{id}").into());
diff --git a/tests/testsuite/print/relative_links/expected/print.html b/tests/testsuite/print/relative_links/expected/print.html
index 2dfbff2059..bff4ce1c65 100644
--- a/tests/testsuite/print/relative_links/expected/print.html
+++ b/tests/testsuite/print/relative_links/expected/print.html
@@ -9,10 +9,10 @@ <h1 id="testing-relative-links-for-the-print-page"><a class="header" href="#test
 <p>A <a href="#some-section">fragment link</a> should work.</p>
 <p>Link <a href="../std/foo/bar.html">outside</a>.</p>
 <p>Link <a href="../std/foo/bar.html#panic">outside with anchor</a>.</p>
-<p>Link <a href="../first/alpha/beta.html">inside but doesn’t exist</a>.
-Link <a href="#anchor">inside but doesn’t exist with anchor</a>.
-Link <a href="../first/alpha/gamma.html">inside to html</a>.
-Link <a href="#anchor">inside to html with anchor</a>.</p>
+<p>Link <a href="first/alpha/beta.html">inside but doesn’t exist</a>.
+Link <a href="first/alpha/beta.html#anchor">inside but doesn’t exist with anchor</a>.
+Link <a href="first/alpha/gamma.html">inside to html</a>.
+Link <a href="first/alpha/gamma.html#anchor">inside to html with anchor</a>.</p>
 <p><img src="images/picture.png" alt="Some image"></p>
 <p><a href="#first-nested">HTML Link</a></p>
 <img src="images/picture.png" alt="raw html">