A command to check if migrations need to be generated

[edigaryev]

I'm trying to improve CI pipeline to prevent situations where SQLAlchemy models are added or changed, but no Alembic migration is written or generated by the commit author from hitting the production branch.

alembic --help doesn't seem to provide any helpful commands for this case, yet it already has all the metadata required (target_metadata variable) and the database credentials in env.py to make this happen.

It would be nice to have this functionality as a separate Alembic command, e.g. alembic check.

(copied and slightly edited from my StackOverflow question: https://stackoverflow.com/questions/61374525/how-do-i-check-if-alembic-migrations-need-to-be-generated)

[zzzeek]

the https://pypi.org/project/alembic-autogen-check/ tool does this. there's discussion over this tool as well as how to do this internally over at #724. As the maintainer of autogen-check does not appear to be responsive we can look to integrate the recipe given in #724.