Fix NextLink prefetch side effect on unsigned claims persistance (#4325)

Author: spastorelli

packages/gitbook/src/components/primitives/Link.tsx

@@ -157,9 +157,14 @@ export function Link(props: LinkProps) {
         );
     }
 
-    // Not sure why yet, but it seems necessary to force prefetch to true
-    // default behavior doesn't seem to properly use the client router cache.
-    const _prefetch = prefetch === null || prefetch === undefined ? true : prefetch;
+    // Not sure why yet, but forcing prefetch to true seems necessary for the
+    // client router cache to be used properly.
+    //
+    // However, we need to disable prefetch for links with query params that
+    // can trigger server-side side effects, such as persisting visitor claims in a
+    // cookie or starting the assistant. Automatic RSC prefetch requests can otherwise
+    // trigger those effects without user intent.
+    const _prefetch = hasSideEffectQueryParams(href) ? false : (prefetch ?? true);
 
     return (
         <NextLink
@@ -175,6 +180,31 @@ export function Link(props: LinkProps) {
     );
 }
 
+/**
+ * Whether the given href carries query params that have a server-side side effect when fetched:
+ *   - `visitor.*` params persist unsigned visitor claims into the `gitbook-visitor-public` cookie.
+ *   - `ask` triggers the assistant & `q` the search.
+ *
+ * NextLink automatically prefetches links (RSC requests) on hover/viewport, which would fire those
+ * side effects without any user intent, so such links should not be prefetched.
+ */
+function hasSideEffectQueryParams(href: string): boolean {
+    const baseURL = typeof window !== 'undefined' ? window.location.origin : 'http://localhost';
+    const linkURL = URL.canParse(href) ? new URL(href) : new URL(href, baseURL);
+
+    if (linkURL.searchParams.get('ask') !== null || linkURL.searchParams.get('q') !== null) {
+        return true;
+    }
+
+    for (const key of linkURL.searchParams.keys()) {
+        if (key.startsWith('visitor.')) {
+            return true;
+        }
+    }
+
+    return false;
+}
+
 /**
  * A box used to contain a link overlay.
  * It is used to create a clickable area that can contain other elements.