どうしても Next.js で Server Function から 400 を返したい者の悪あがき

action.ts

"use server";

import { mock } from 'node:test';

const httpAccessFallbackModule = await import("next/dist/client/components/http-access-fallback/http-access-fallback.js");

// ref: https://github.com/vercel/next.js/blob/6f763ecfd48acc3593f8a10328aef9358fdb7c75/packages/next/src/client/components/http-access-fallback/http-access-fallback.ts
mock.module('next/dist/client/components/http-access-fallback/http-access-fallback.js', {
  namedExports: {
    ...httpAccessFallbackModule,
    isHTTPAccessFallbackError: (error: unknown): error is any => {
      if (
        typeof error !== 'object' ||
        error === null ||
        !('digest' in error) ||
        typeof error.digest !== 'string'
      ) {
        return false
      }
      const [prefix] = error.digest.split(';');

      return (
        prefix === httpAccessFallbackModule.HTTP_ERROR_FALLBACK_ERROR_CODE
      );
    },
  },
});
function badRequest(): never {
  const digest = `${httpAccessFallbackModule.HTTP_ERROR_FALLBACK_ERROR_CODE};400`;
  const error = new Error(digest);
  // @ts-expect-error
  error.digest = digest;
  throw error;
}

export async function greet(name: string): Promise<string> {
  badRequest();
  return `Hello, ${name}!`;
}

result.md

• Turbopack の壁が立ちはだかり、無事敗北
  • 
• そもそも node:test をアプリケーションコードで使ってはならない
• モンキーパッチも極力避けるべき
  • モンキーパッチするよりは https://www.npmjs.com/package/patch-package や yarn patch, pnpm patch を使うほうがマシ
• 大人しく vercel/next.js#49302 の解決を待ちましょう