Add Custom commands

[cleder]

I'd like to add a custom command to alembic that produces a data migration.

Gemini and chatGPT hallucinate something about:

Create a custom Alembic command by subclassing Command from Alembic's commands module.

so this may have been possible with a previous version.

[zzzeek]

sure, it's CommandLine and it's right here: https://github.com/sqlalchemy/alembic/blob/main/alembic/config.py#L347 source code is straightforward

[cleder]

Sure, I can maintain a fork the question was more if it is possible with a plugin like system.

[CaselIT]

Not right now. I'm not sure if there could be something simple that we could support.
You could likely subclass CommandLine to add the new option and generate a script that uses the new class.

Your would not need to maintain a fork, but I think another command name other than alembic would be needed

[mikeroll]

My proposal for improving such a use case: #1611