update to next 16.2

Update Next.js from 15.1.12 to 16.2.0, React from ^19.0.0 to 19.2.4,
and ESLint from 7.x to ^9 with flat config migration.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: lukesandberg

.eslintignore

@@ -84,15 +84,19 @@ function parseExpectedErrorsEntries(rawEntries) {
 
   if (parsed && typeof parsed === 'object') {
     for (const [key, value] of Object.entries(parsed)) {
-      entries[key] = normalizeEntryValues(Array.isArray(value) ? value.flat() : value);
+      entries[key] = normalizeEntryValues(
+        Array.isArray(value) ? value.flat() : value
+      );
     }
   }
 
   return entries;
 }
 
 function parseExpectedErrorsToken(tokenText) {
-  const match = tokenText.match(/^\{\s*expectedErrors\s*:\s*(\{[\s\S]*\})\s*\}$/);
+  const match = tokenText.match(
+    /^\{\s*expectedErrors\s*:\s*(\{[\s\S]*\})\s*\}$/
+  );
   if (!match) {
     return null;
   }
@@ -103,7 +107,7 @@ function parseExpectedErrorsToken(tokenText) {
 
   try {
     entries = parseExpectedErrorsEntries(entriesSource);
-  } catch (error) {
+  } catch (_error) {
     parseError = true;
     entries = {};
   }
@@ -203,7 +207,9 @@ function cloneMetadata(metadata) {
 }
 
 function findExpectedErrorsToken(metadata) {
-  return metadata.tokens.find((token) => token.type === 'expectedErrors') || null;
+  return (
+    metadata.tokens.find((token) => token.type === 'expectedErrors') || null
+  );
 }
 
 function getCompilerExpectedLines(metadata) {

.eslintrc

@@ -82,7 +82,7 @@ function runReactCompiler(code, filename) {
       configFile: false,
       babelrc: false,
     });
-  } catch (error) {
+  } catch (_error) {
     return {...result, diagnostics: []};
   }
 
@@ -98,17 +98,19 @@ function runReactCompiler(code, filename) {
       continue;
     }
 
-    const loc = typeof detail.primaryLocation === 'function'
-      ? detail.primaryLocation()
-      : null;
+    const loc =
+      typeof detail.primaryLocation === 'function'
+        ? detail.primaryLocation()
+        : null;
 
     if (loc == null || typeof loc === 'symbol') {
       continue;
     }
 
-    const message = typeof detail.printErrorMessage === 'function'
-      ? detail.printErrorMessage(result.sourceCode, {eslint: true})
-      : detail.description || 'Unknown React Compiler error';
+    const message =
+      typeof detail.printErrorMessage === 'function'
+        ? detail.printErrorMessage(result.sourceCode, {eslint: true})
+        : detail.description || 'Unknown React Compiler error';
 
     diagnostics.push({detail, loc, message});
   }

eslint-local-rules/rules/metadata.js

@@ -0,0 +1,87 @@
+import nextCoreWebVitals from "eslint-config-next/core-web-vitals";
+import reactCompiler from "eslint-plugin-react-compiler";
+import localRules from "eslint-plugin-local-rules";
+import globals from "globals";
+import tsParser from "@typescript-eslint/parser";
+import parser from "./eslint-local-rules/parser.js";
+
+// Extract plugin instances from next's config to avoid
+// "Cannot redefine plugin" errors in flat config.
+function getNextPlugin(name) {
+    return nextCoreWebVitals.find((c) => c.plugins?.[name])?.plugins[name];
+}
+const tsPlugin = getNextPlugin("@typescript-eslint");
+const reactHooksPlugin = getNextPlugin("react-hooks");
+
+export default [
+    {
+        ignores: [
+            "**/scripts",
+            "**/plugins",
+            "**/next.config.js",
+            "**/.claude/",
+            "**/worker-bundle.dist.js",
+        ],
+    },
+    ...nextCoreWebVitals,
+    {
+        plugins: {
+            "@typescript-eslint": tsPlugin,
+            "react-hooks": reactHooksPlugin,
+            "react-compiler": reactCompiler,
+            "local-rules": localRules,
+        },
+
+        languageOptions: {
+            globals: Object.fromEntries(
+                Object.entries({
+                    ...globals.node,
+                    ...globals.commonjs,
+                    ...globals.browser,
+                }).map(([key, value]) => [key.trim(), value])
+            ),
+
+            parser: tsParser,
+        },
+
+        rules: {
+            "no-unused-vars": "off",
+
+            "@typescript-eslint/no-unused-vars": ["error", {
+                varsIgnorePattern: "^_",
+                caughtErrorsIgnorePattern: "^_",
+            }],
+
+            "react-hooks/exhaustive-deps": "error",
+
+            "react/no-unknown-property": ["error", {
+                ignore: ["meta"],
+            }],
+
+            // New rules in react-hooks plugin — pre-existing patterns need refactoring
+            "react-hooks/set-state-in-effect": "warn",
+            "react-hooks/refs": "warn",
+
+            "react-compiler/react-compiler": "error",
+            "local-rules/lint-markdown-code-blocks": "error",
+        },
+    },
+    {
+        files: ["src/content/**/*.md"],
+
+        languageOptions: {
+            parser: parser,
+            ecmaVersion: 5,
+            sourceType: "module",
+        },
+
+        rules: {
+            "no-unused-vars": "off",
+            "@typescript-eslint/no-unused-vars": "off",
+            "react-hooks/exhaustive-deps": "off",
+            "react/no-unknown-property": "off",
+            "react-compiler/react-compiler": "off",
+            "local-rules/lint-markdown-code-blocks": "error",
+        },
+    },
+];

eslint-local-rules/rules/react-compiler.js

@@ -1,5 +1,6 @@
 /// <reference types="next" />
 /// <reference types="next/image-types/global" />
+import './.next/types/routes.d.ts';
 
 // NOTE: This file should not be edited
 // see https://nextjs.org/docs/pages/api-reference/config/typescript for more information.

eslint.config.mjs

@@ -13,12 +13,29 @@
  * @type {import('next').NextConfig}
  **/
 const nextConfig = {
+  turbopack: {
+    resolveAlias: {
+      // Don't bundle the shim unnecessarily.
+      'use-sync-external-store/shim': 'react',
+      // ESLint depends on the CommonJS version of esquery,
+      // but Webpack loads the ESM version by default. This
+      // alias ensures the correct version is used.
+      //
+      // More info:
+      // https://github.com/reactjs/react.dev/pull/8115
+      esquery: 'esquery/dist/esquery.min.js',
+      // Replace transitive dependencies with lightweight shims.
+      raf: './src/utils/rafShim.js',
+      process: './src/utils/processShim.js',
+    },
+  },
   pageExtensions: ['jsx', 'js', 'ts', 'tsx', 'mdx', 'md'],
   reactStrictMode: true,
   experimental: {
     scrollRestoration: true,
-    reactCompiler: true,
+    turbopackImportTypeText: true,
   },
+  reactCompiler: true,
   async rewrites() {
     return {
       beforeFiles: [
@@ -44,58 +61,6 @@ const nextConfig = {
     };
   },
   env: {},
-  webpack: (config, {dev, isServer, ...options}) => {
-    if (process.env.ANALYZE) {
-      const {BundleAnalyzerPlugin} = require('webpack-bundle-analyzer');
-      config.plugins.push(
-        new BundleAnalyzerPlugin({
-          analyzerMode: 'static',
-          reportFilename: options.isServer
-            ? '../analyze/server.html'
-            : './analyze/client.html',
-        })
-      );
-    }
-
-    // Don't bundle the shim unnecessarily.
-    config.resolve.alias['use-sync-external-store/shim'] = 'react';
-
-    // ESLint depends on the CommonJS version of esquery,
-    // but Webpack loads the ESM version by default. This
-    // alias ensures the correct version is used.
-    //
-    // More info:
-    // https://github.com/reactjs/react.dev/pull/8115
-    config.resolve.alias['esquery'] = 'esquery/dist/esquery.min.js';
-
-    const {IgnorePlugin, NormalModuleReplacementPlugin} = require('webpack');
-    config.plugins.push(
-      new NormalModuleReplacementPlugin(
-        /^raf$/,
-        require.resolve('./src/utils/rafShim.js')
-      ),
-      new NormalModuleReplacementPlugin(
-        /^process$/,
-        require.resolve('./src/utils/processShim.js')
-      ),
-      new IgnorePlugin({
-        checkResource(resource, context) {
-          if (
-            /\/eslint\/lib\/rules$/.test(context) &&
-            /\.\/[\w-]+(\.js)?$/.test(resource)
-          ) {
-            // Skips imports of built-in rules that ESLint
-            // tries to carry into the bundle by default.
-            // We only want the engine and the React rules.
-            return true;
-          }
-          return false;
-        },
-      })
-    );
-
-    return config;
-  },
 };
 
 module.exports = nextConfig;

next-env.d.ts

@@ -4,12 +4,11 @@
   "private": true,
   "license": "CC",
   "scripts": {
-    "analyze": "ANALYZE=true next build",
+    "analyze": "next experimental-analyze",
     "dev": "next-remote-watch ./src/content",
-    "prebuild:rsc": "node scripts/buildRscWorker.mjs",
     "build": "node scripts/buildRscWorker.mjs && next build && node --experimental-modules ./scripts/downloadFonts.mjs",
-    "lint": "next lint && eslint \"src/content/**/*.md\"",
-    "lint:fix": "next lint --fix && eslint \"src/content/**/*.md\" --fix",
+    "lint": "eslint . && eslint \"src/content/**/*.md\"",
+    "lint:fix": "eslint --fix . && eslint \"src/content/**/*.md\" --fix",
     "format:source": "prettier --config .prettierrc --write \"{plugins,src}/**/*.{js,ts,jsx,tsx,css}\"",
     "nit:source": "prettier --config .prettierrc --list-different \"{plugins,src}/**/*.{js,ts,jsx,tsx,css}\"",
     "prettier": "yarn format:source",
@@ -36,13 +35,12 @@
     "classnames": "^2.2.6",
     "debounce": "^1.2.1",
     "github-slugger": "^1.3.0",
-    "next": "15.1.12",
+    "next": "16.2.0",
     "next-remote-watch": "^1.0.0",
     "parse-numeric-range": "^1.2.0",
-    "raw-loader": "^4.0.2",
-    "react": "^19.0.0",
+    "react": "19.2.4",
     "react-collapsed": "4.0.4",
-    "react-dom": "^19.0.0",
+    "react-dom": "19.2.4",
     "remark-frontmatter": "^4.0.1",
     "remark-gfm": "^3.0.1"
   },
@@ -58,8 +56,9 @@
     "@types/mdx-js__react": "^1.5.2",
     "@types/node": "^14.6.4",
     "@types/parse-numeric-range": "^0.0.1",
-    "@types/react": "^19.0.0",
-    "@types/react-dom": "^19.0.0",
+    "@types/prop-types": "^15.7.15",
+    "@types/react": "19.2.14",
+    "@types/react-dom": "19.2.3",
     "@typescript-eslint/eslint-plugin": "^5.36.2",
     "@typescript-eslint/parser": "^5.36.2",
     "asyncro": "^3.0.0",
@@ -68,8 +67,8 @@
     "babel-plugin-react-compiler": "^1.0.0",
     "chalk": "4.1.2",
     "esbuild": "^0.24.0",
-    "eslint": "7.x",
-    "eslint-config-next": "12.0.3",
+    "eslint": "^9",
+    "eslint-config-next": "16.2.0",
     "eslint-config-react-app": "^5.2.1",
     "eslint-plugin-flowtype": "4.x",
     "eslint-plugin-import": "2.x",
@@ -104,20 +103,18 @@
     "rss": "^1.2.2",
     "tailwindcss": "^3.4.1",
     "typescript": "^5.7.2",
-    "unist-util-visit": "^2.0.3",
-    "webpack-bundle-analyzer": "^4.5.0"
+    "unist-util-visit": "^2.0.3"
   },
   "engines": {
     "node": ">=16.8.0"
   },
-  "nextBundleAnalysis": {
-    "budget": null,
-    "budgetPercentIncreaseRed": 10,
-    "showDetails": true
-  },
   "lint-staged": {
     "*.{js,ts,jsx,tsx,css}": "yarn prettier",
     "src/**/*.md": "yarn fix-headings"
   },
-  "packageManager": "yarn@1.22.22"
+  "packageManager": "yarn@1.22.22",
+  "resolutions": {
+    "@types/react": "19.2.14",
+    "@types/react-dom": "19.2.3"
+  }
 }