Migrate to Next.js 16, React 19, and Fumadocs v16

- Updated Next.js from 15.1.0 to 16.0.7
- Updated React to 19.2.1 (latest)
- Updated Fumadocs packages from v14 to v16.2.3
- Updated Tailwind CSS to v4.1.17 with new PostCSS plugin
- Fixed breaking changes:
  - Updated async request APIs (params already awaited)
  - Fixed Fumadocs provider imports
  - Updated theme toggle to use next-themes directly
  - Fixed sidebar components API changes
  - Updated source imports and exports
  - Removed deprecated patch file
- Updated all dev dependencies to latest versions

Author: oscartbeaumont

app/(home)/Navbar.tsx

@@ -1,8 +1,18 @@
-import { ThemeToggle } from "fumadocs-ui/components/layout/theme-toggle";
+"use client";
+
 import { SiteLogo } from "./SiteLogo";
 import Link from "next/link";
+import { useTheme } from "next-themes";
+import { useEffect, useState } from "react";
 
 export function Navbar() {
+  const { theme, setTheme } = useTheme();
+  const [mounted, setMounted] = useState(false);
+
+  useEffect(() => {
+    setMounted(true);
+  }, []);
+
   return (
     <>
       <div className="backdrop-blur-sm w-full h-16 px-4 flex items-center justify-between fixed top-0">
@@ -11,7 +21,14 @@ export function Navbar() {
         </Link>
 
         <div className="flex items-center space-x-4">
-          <ThemeToggle />
+          {mounted && (
+            <button
+              onClick={() => setTheme(theme === "dark" ? "light" : "dark")}
+              className="p-2 rounded-md hover:bg-gray-200 dark:hover:bg-gray-700"
+            >
+              {theme === "dark" ? "🌞" : "🌙"}
+            </button>
+          )}
         </div>
       </div>
     </>

app/docs/SidebarItem.tsx

@@ -1,11 +1,10 @@
 "use client";
 
 import { CratesIoLogo, NpmLogo } from "@/lib/logos";
-import { type SidebarComponents } from "fumadocs-ui/layouts/docs/shared";
-import { SidebarItem } from "fumadocs-ui/layouts/docs/sidebar";
+import { SidebarItem } from "fumadocs-ui/components/sidebar/base";
 
-export const components: Partial<SidebarComponents> = {
-  Item: ({ item }) => {
+export const components = {
+  Item: ({ item }: any) => {
     // TODO: generalise this and configure it for all revelant links
     if (item.url === "/docs/rspc/client/vanilla") {
       return (

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

@@ -21,12 +21,11 @@ export default async function Page(props: {
     <DocsPage
       toc={page.data.toc}
       full={page.data.full}
-      lastUpdate={page.data.lastModified}
       editOnGithub={{
         repo: "website",
         owner: "specta-rs",
         sha: "main",
-        path: `content/docs/${page.file.path}`,
+        path: `content/docs/${page.slugs.join('/')}`,
       }}
     >
       <DocsTitle>{page.data.title}</DocsTitle>

app/layout.tsx

@@ -1,4 +1,4 @@
-import { RootProvider } from "fumadocs-ui/provider";
+import { RootProvider } from "fumadocs-ui/provider/next";
 import { Metadata } from "next";
 import { Inter } from "next/font/google";
 import type { ReactNode } from "react";

lib/source.ts

@@ -1,13 +1,13 @@
-import { docs, meta } from "@/.source";
+import { docs, meta } from "../.source/server";
+import { toFumadocsSource } from "fumadocs-mdx/runtime/server";
 import Image from "next/image";
-import { createMDXSource } from "fumadocs-mdx";
 import { loader } from "fumadocs-core/source";
 import { createElement } from "react";
 import { CratesIoLogo, NpmLogo } from "./logos";
 
 export const source = loader({
   baseUrl: "/docs",
-  source: createMDXSource(docs, meta),
+  source: toFumadocsSource(docs, meta),
   icon(icon) {
     if (!icon) return;
 

package.json

@@ -14,10 +14,12 @@
     "fumadocs-ui": "16.2.3",
     "next": "16.0.7",
     "next-sitemap": "^4.2.3",
+    "next-themes": "^0.4.6",
     "react": "^19.2.1",
     "react-dom": "^19.2.1"
   },
   "devDependencies": {
+    "@tailwindcss/postcss": "^4.1.17",
     "@types/mdx": "^2.0.13",
     "@types/node": "24.10.1",
     "@types/react": "^19.2.7",
@@ -30,8 +32,5 @@
     "typescript": "^5.9.3"
   },
   "pnpm": {
-    "patchedDependencies": {
-      "fumadocs-ui": "patches/fumadocs-ui.patch"
-    }
   }
 }