Migrations system: `sqlite_utils.Migrations` and `sqlite-utils migrate` command, ported from `sqlite-migrate`

[simonw]

The https://github.com/simonw/sqlite-migrate library is still in beta but it's been proving itself for 3 years now. It's time it became a feature of sqlite-utils.

[simonw]

My plan is to do a sqlite-migrate release that pins to <4, then publish sqlite-utils 4 with this new feature and straight after to a sqlite-migrate release than pins >=4 and imports stuff from the new home.

[simonw]

Actually since there are sqlite-utils 4.x alphas out there that do NOT have the migrate functionality in I think the correct pin for sqlite-migrate is:

dependencies = [
    "sqlite-utils!=4.0,<4.0.post0"
]

[simonw]

Spotted a design flaw in this command, inherited from sqlite-migrate:

sqlite-utils migrate creatures.db path/to/migrations.py --stop-before add_weight

That path/to/migrations.py file might actually contain more than one migration set. If they both have a migration called add_weight both will stop there. This is a little confusing.

I want to maintain backwards compatibility with sqlite-migrate so I think I'll solve that like this:

sqlite-utils migrate creatures.db path/to/migrations.py --stop-before creatures:add_weight --stop-before sales:drop_index

You can optionally namespace the stop before indicators - migration_set:name_of_migration - and you can pass more than one --stop-before.

The old form still works - if you don't include a : we match on name and ignore the migration set.