React Vendoring Agent Skill

React Vendoring

Use this skill for changes touching vendored React, react-server-dom-webpack/*, or react-server layer boundaries.

App Router Vendoring

React is NOT resolved from node_modules for App Router. It's vendored into packages/next/src/compiled/ during pnpm build (task: copy_vendor_react() in taskfile.js). Pages Router resolves React from node_modules normally.

• Two channels: stable (compiled/react/) and experimental (compiled/react-experimental/). The runtime bundle webpack config aliases to the correct channel via makeAppAliases({ experimental }).

entry-base.ts Boundary

Only entry-base.ts is compiled in rspack's (react-server) layer. ALL imports from react-server-dom-webpack/* (Flight server/static APIs) must go through entry-base.ts. Other files like stream-ops.node.ts or app-render.tsx must access Flight APIs via the ComponentMod parameter (which is the entry-base.ts module exposed through the app-page.ts build template).

Direct imports from react-server-dom-webpack/server.node or react-server-dom-webpack/static in files outside entry-base.ts will fail at runtime with "The react-server condition must be enabled". Dev mode may mask this error, but production workers fail immediately.

Type Declarations

packages/next/types/$$compiled.internal.d.ts contains declare module blocks for vendored React packages. When adding new APIs (e.g. renderToPipeableStream, prerenderToNodeStream), you must add type declarations here. The bare specifier types (e.g. declare module 'react-server-dom-webpack/server') are what source code in src/ imports against.

Adding Node.js-Only React APIs

These exist in .node builds but not in the type definitions. Steps:

• Add type declarations to $$compiled.internal.d.ts.
• Export the API from entry-base.ts behind a process.env guard.
• Access it via ComponentMod in other files.

// In entry-base.ts (react-server layer) only:
/* eslint-disable import/no-extraneous-dependencies */
export let renderToPipeableStream: ... | undefined
if (process.env.__NEXT_USE_NODE_STREAMS) {
  renderToPipeableStream = (
    require('react-server-dom-webpack/server.node') as typeof import('react-server-dom-webpack/server.node')
  ).renderToPipeableStream
} else {
  renderToPipeableStream = undefined
}
/* eslint-enable import/no-extraneous-dependencies */

// In other files, access via ComponentMod:
ComponentMod.renderToPipeableStream!(payload, clientModules, opts)

ESLint Practical Rule

For guarded runtime require() blocks that need import/no-extraneous-dependencies suppression, prefer scoped block disable/enable. If using eslint-disable-next-line, the comment must be on the line immediately before the require() call, NOT before the const declaration. When the const and require() are on different lines, this is error-prone.

Turbopack Remap

react-server-dom-webpack/* is silently remapped to react-server-dom-turbopack/* by Turbopack's import map. Code says "webpack" everywhere, but Turbopack gets its own bindings at runtime. This affects debugging: stack traces and error messages will reference the turbopack variant.

Related Skills

• $flags - flag wiring (config/schema/define-env/runtime env)
• $dce-edge - DCE-safe require patterns and edge constraints
• $runtime-debug - reproduction and verification workflow