Fix redirects in safari, by moving the redirect js script into the 404 page instead of checking if we're on 404 via the API.

404.rst

@@ -22,3 +22,33 @@ Page not found
         <a href="#" onclick="$('#rtd-search-form [name=\\'q\\']').focus()">Search docs</a>
         box on the left or <a href="/">go to the homepage</a>.
     </p>
+
+    <script>
+    // Check for redirects if on a currently invalid page.
+    // This is done in JavaScript, as we exceed Read the Docs' limit for the amount of redirects configurable.
+    // When testing this feature on a local web server, replace the URL below with just `/_static/redirects.csv`.
+    fetch("/en/latest/_static/redirects.csv")
+      .then(response => response.text())
+      .then(csvText => {
+        const lines = csvText.trim().split('\n');
+        for (const line of lines) {
+          if (!line.trim()) {
+            continue;
+          }
+          const [from, to] = line.split(',').map(s => s.trim());
+          if (from && to) {
+            if (window.location.pathname.endsWith(from)) {
+              if (to.startsWith('https://')) {
+                window.location.replace(to);
+              } else {
+                const newUrl = window.location.href.replace(window.location.pathname, to);
+                window.location.replace(newUrl);
+              }
+            }
+          }
+        }
+      })
+      .catch(err => {
+        console.error("Couldn't fetch redirects list:", err);
+      });
+    </script>

_static/js/custom.js

@@ -297,37 +297,6 @@ const registerGiscus = function () {
 };
 
 $(document).ready(() => {
-  const httpResponseStatus = window.performance.getEntries()[0].responseStatus;
-  if (httpResponseStatus === 404) {
-    // Check for redirects if on a currently invalid page.
-    // This is done in JavaScript, as we exceed Read the Docs' limit for the amount of redirects configurable.
-    // When testing this feature on a local web server, replace the URL below with just `/_static/redirects.csv`.
-    fetch("/en/latest/_static/redirects.csv")
-      .then(response => response.text())
-      .then(csvText => {
-        const lines = csvText.trim().split('\n');
-        for (const line of lines) {
-          if (!line.trim()) {
-            continue;
-          }
-          const [from, to] = line.split(',').map(s => s.trim());
-          if (from && to) {
-            if (window.location.pathname.endsWith(from)) {
-              if (to.startsWith('https://')) {
-                window.location.replace(to);
-              } else {
-                const newUrl = window.location.href.replace(window.location.pathname, to);
-                window.location.replace(newUrl);
-              }
-            }
-          }
-        }
-      })
-      .catch(err => {
-        console.error("Couldn't fetch redirects list:", err);
-      });
-  }
-
   // Remove the search match highlights from the page, and adjust the URL in the
   // navigation history.
   const url = new URL(location.href);