NestJS CLI tool to dump openapi.json

gen-openapi.ts

// Help: https://stackoverflow.com/questions/72852736/generating-swagger-json-file-without-running-nest-js-server
// NestJS 11
import * as path from 'path';
import { writeFileSync } from 'fs';
import { DataType, newDb } from 'pg-mem';
import { DataSource } from 'typeorm';
import { DocumentBuilder, SwaggerModule } from '@nestjs/swagger';
import { Test } from '@nestjs/testing';
import { AppModule } from '../src/app.module';

async function dumpSwagger() {
  // Setup in-memory Postgres
  const db = newDb();
  db.public.registerFunction({
    name: 'current_database',
    args: [],
    returns: DataType.text,
    implementation: () => 'localdb',
  });
  db.public.registerFunction({
    name: 'version',
    args: [],
    returns: DataType.text,
    implementation: () => '1',
  });

  const datasource = (await db.adapters.createTypeormDataSource({
    type: 'postgres',
    autoLoadEntities: true,
    synchronize: true,
  })) as DataSource;

  await datasource.initialize();
  await datasource.synchronize();

  const moduleFixture = await Test.createTestingModule({
      imports: [AppModule],
    })
      .overrideProvider(DataSource)
      .useValue(datasource)
      .compile();

  let app = moduleFixture.createNestApplication();

  // Create Swagger
  const config = new DocumentBuilder()
    .setTitle('NestJS App')
    .setDescription('NestJS App description')
    .setVersion('1.0')
    .build();

  const document = SwaggerModule.createDocument(app, config);

  await app.close();
  
  return document;
}

dumpSwagger().then(document => {
  const jsonContent = JSON.stringify(document, null, 2);
  
  const outputFilePath = process.argv[2];
  if (outputFilePath) {
    // Write to specified file
    const resolvedPath = path.resolve(process.cwd(), outputFilePath);
    writeFileSync(resolvedPath, jsonContent, 'utf8');
    console.log(`Swagger JSON dumped to ${resolvedPath}`);
  } else {
    // Dump to stdout
    console.log(jsonContent);
  }
}).catch(err => {
  console.error(err);
  process.exit(1);
});