Issue description

When defining an async datasource to use for migrations the typeorm CLI breaks

Expected Behavior

It should be possible to define async DataSource according to:
#8914

And use that for configuring TypeOrm.

Actual Behavior

When declaring an async data source as mentioned in the original issue #8914

const buildDataSource = async () => {
  await ConfigModule.envVariablesLoaded;

  return new DataSource({
    type: 'postgres',
    url: process.env.DATABASE_URL,
    entities: ['dist/domain/**/*.entity.js'],
    migrations: ['dist/database/migrations/*.js'],
  });
};

export default buildDataSource();

It fails with

Error during migration generation:
TypeError: dataSourceFileExports is not iterable
    at Function.loadDataSource (/Some/Path/backend/node_modules/src/commands/CommandUtils.ts:37:34)
    at async Object.handler ((/Some/Path/backend/node_modules/src/commands/MigrationGenerateCommand.ts:73:26)

I have tried numerous approaches to the export but they basically all fail.

Steps to reproduce

Define an async DataSource and run the migrate:generate or migrate:run command.

My Environment

Additional Context

After some debugging it turns out that the problem lies in the CommandUtils.ts - checking for someting instanceof Promise is not stable and it does not work on my machine ™️. The check fails and thus passes the promise up the chain to the InstanceChecker which naturally fails.

I have a PR coming.

Relevant Database Driver(s)

• aurora-mysql
• aurora-postgres
• better-sqlite3
• cockroachdb
• cordova
• expo
• mongodb
• mysql
• nativescript
• oracle
• postgres
• react-native
• sap
• spanner
• sqlite
• sqlite-abstract
• sqljs
• sqlserver

Are you willing to resolve this issue by submitting a Pull Request?

Yes, I have the time, and I know how to start.