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.

Author: ehuss

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());

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">