fix: preserve Rustdoc fragments in permalink links

crates/bin/docs_rs_web/src/handlers/rustdoc.rs

@@ -2823,6 +2823,36 @@ mod test {
         })
     }
 
+    #[test]
+    fn permalink_retains_rustdoc_fragment() {
+        async_wrapper(|env| async move {
+            env.fake_release()
+                .await
+                .name("testing")
+                .version("0.1.0")
+                .rustdoc_file("testing/index.html")
+                .create()
+                .await?;
+
+            let dom = kuchikiki::parse_html().one(
+                env.web_app()
+                    .await
+                    .get("/testing/latest/testing/index.html")
+                    .await?
+                    .text()
+                    .await?,
+            );
+
+            let permalink = dom.select_first("#permalink").expect("permalink link");
+            assert_eq!(
+                permalink.attributes.borrow().get("data-fragment"),
+                Some("retain")
+            );
+
+            Ok(())
+        })
+    }
+
     #[test]
     fn test_repository_link_in_topbar_dropdown_github() {
         async_wrapper(|env| async move {

crates/bin/docs_rs_web/templates/rustdoc/topbar.html

@@ -29,7 +29,7 @@
 
                     {%- if metadata.req_version.to_string() == "latest" -%}
                     <li class="pure-menu-item">
-                        <a href="{% if permalink_path is defined %}{{permalink_path|safe}}{% endif %}" class="pure-menu-link description" id="permalink" title="Get a link to this specific version">
+                        <a href="{% if permalink_path is defined %}{{permalink_path|safe}}{% endif %}" class="pure-menu-link description" id="permalink" data-fragment="retain" title="Get a link to this specific version">
                             {{- crate::icons::IconLink.render_solid(false, false, "") }} Permalink
                         </a>
                     </li>

gui-tests/permalink-fragment.goml

@@ -0,0 +1,10 @@
+// The permalink link must retain the fragment from the current rustdoc page.
+go-to: |DOC_PATH| + "/sysinfo/latest/sysinfo/index.html#section"
+wait-for: "#permalink"
+assert-document-property: ({"URL": "#section"}, ENDS_WITH)
+
+// The fragment is added on mouseover because browsers do not send it to the server.
+move-cursor-to: "#permalink"
+assert: "#permalink"
+click: "#permalink"
+assert-document-property: ({"URL": "#section"}, ENDS_WITH)