add 404 page and sitemap

app/(docs)/[[...slug]]/page.tsx

@@ -5,8 +5,8 @@ import {
   DocsPage,
   DocsTitle,
   MarkdownCopyButton,
-  ViewOptionsPopover,
 } from 'fumadocs-ui/layouts/notebook/page';
+import { ViewOptionsPopover } from '@/components/view-options';
 import { notFound } from 'next/navigation';
 import { getMDXComponents } from '@/components/mdx';
 import type { Metadata } from 'next';
@@ -77,7 +77,10 @@ export async function generateMetadata(props: PageProps<'/[[...slug]]'>): Promis
     description: page.data.description,
     alternates: {
       canonical: page.url,
-      types: { 'text/markdown': getPageMarkdownUrl(page).url },
+      types: {
+        'text/markdown': getPageMarkdownUrl(page).url,
+        'application/xml': '/sitemap.xml',
+      },
     },
     openGraph: {
       images: '/images/home-social-graph.png',

app/(docs)/not-found.tsx

@@ -0,0 +1,30 @@
+import type { Metadata } from 'next';
+import type { ReactNode } from 'react';
+import type * as PageTree from 'fumadocs-core/page-tree';
+import { NotFoundPage, type NotFoundLink } from '@/components/not-found';
+import { getNavigationTree } from '@/lib/navigation';
+
+export const metadata: Metadata = {
+  title: 'Page Not Found',
+};
+
+function label(name: ReactNode) {
+  return typeof name === 'string' ? name : null;
+}
+
+function flatten(nodes: PageTree.Node[]): NotFoundLink[] {
+  const links: NotFoundLink[] = [];
+  for (const node of nodes) {
+    if (node.type === 'page') {
+      const title = label(node.name);
+      if (title && node.url) links.push({ title, url: node.url });
+      continue;
+    }
+    if (node.type === 'folder') links.push(...flatten(node.children));
+  }
+  return links;
+}
+
+export default function NotFound() {
+  return <NotFoundPage pages={flatten(getNavigationTree().children)} />;
+}