Add CI check to validate externals doc (#62968)

This avoids the need to manually check when these get out of sync by
having an automated check to keep them in sync when one or the other is
updated.

x-ref: #62966

Closes NEXT-2734

package.json

@@ -30,7 +30,8 @@
     "lint-typescript": "turbo run typescript",
     "lint-eslint": "eslint . --ext js,jsx,ts,tsx --max-warnings=0 --config .eslintrc.json --no-eslintrc",
     "lint-no-typescript": "run-p prettier-check lint-eslint lint-language",
-    "types-and-precompiled": "run-p lint-typescript check-precompiled",
+    "types-and-precompiled": "run-p lint-typescript check-precompiled validate-externals-doc",
+    "validate-externals-doc": "node ./scripts/validate-externals-doc.js",
     "lint": "run-p test-types lint-typescript prettier-check lint-eslint lint-language",
     "lint-fix": "pnpm prettier-fix && eslint . --ext js,jsx,ts,tsx --fix --max-warnings=0 --config .eslintrc.json --no-eslintrc",
     "lint-language": "alex .",

scripts/validate-externals-doc.js

@@ -0,0 +1,45 @@
+const fs = require('fs')
+const path = require('path')
+
+const serverExternals = require('../packages/next/src/lib/server-external-packages.json')
+
+const docPath = `docs/02-app/02-api-reference/05-next-config-js/serverComponentsExternalPackages.mdx`
+const docContent = fs.readFileSync(path.join(__dirname, '..', docPath), 'utf8')
+
+const docPkgs = []
+const extraPkgs = []
+const missingPkgs = []
+
+for (let docPkg of docContent.split('opt-ed out:').pop().split('\n')) {
+  docPkg = docPkg.split('`')[1]
+
+  if (!docPkg) {
+    continue
+  }
+  docPkgs.push(docPkg)
+
+  if (!serverExternals.includes(docPkg)) {
+    extraPkgs.push(docPkg)
+  }
+}
+
+for (const pkg of serverExternals) {
+  if (!docPkgs.includes(pkg)) {
+    missingPkgs.push(pkg)
+  }
+}
+
+if (extraPkgs.length || missingPkgs.length) {
+  console.log(
+    'server externals doc out of sync!\n' +
+      `Extra packages included: ` +
+      JSON.stringify(extraPkgs, null, 2) +
+      '\n' +
+      `Missing packages: ` +
+      JSON.stringify(missingPkgs, null, 2) +
+      '\n' +
+      `doc path: ${docPath}`
+  )
+  process.exit(1)
+}
+console.log('server externals doc is in sync')