Rollup merge of #55080 - thanatos:fix-localstorage-crash, r=GuillaumeGomez

Detect if access to localStorage is forbidden by the user's browser

If the user's cookie/persistent storage setting forbid access to `localStorage`, catch the exception and abort the access.

Currently, attempting to use the expand/contract links at the top of the page for structs/consts/etc. fails due to an unhandled error while accessing `localStorage`, if such access is forbidden, as the exception from the failed access propagates all the way out, interrupting the expand/contract. Instead, I would like to degrade gracefully; the access won't happen (the collapse/expand state won't get persisted) but the actual expanding/contracting of the item will go on to succeed.

Fixes #55079

src/librustdoc/html/static/storage.js

@@ -26,8 +26,26 @@ function onEach(arr, func) {
     return false;
 }
 
+function usableLocalStorage() {
+    // Check if the browser supports localStorage at all:
+    if (typeof(Storage) === "undefined") {
+        return false;
+    }
+    // Check if we can access it; this access will fail if the browser
+    // preferences deny access to localStorage, e.g., to prevent storage of
+    // "cookies" (or cookie-likes, as is the case here).
+    try {
+        window.localStorage;
+    } catch(err) {
+        // Storage is supported, but browser preferences deny access to it.
+        return false;
+    }
+
+    return true;
+}
+
 function updateLocalStorage(name, value) {
-    if (typeof(Storage) !== "undefined") {
+    if (usableLocalStorage()) {
         localStorage[name] = value;
     } else {
         // No Web Storage support so we do nothing
@@ -35,7 +53,7 @@ function updateLocalStorage(name, value) {
 }
 
 function getCurrentValue(name) {
-    if (typeof(Storage) !== "undefined" && localStorage[name] !== undefined) {
+    if (usableLocalStorage() && localStorage[name] !== undefined) {
         return localStorage[name];
     }
     return null;