Allow makemigrations to skip database consistency checks

[Tom Forbes]

Currently makemigrations always requires an active database connection, due to it executing loader.check_consistent_history() here: ​https://github.com/django/django/blob/290d8471bba35980f3e228f9c171afc40f2550fa/django/core/management/commands/makemigrations.py#L93-L101

Sometimes you are making a change on a machine that doesn't have a database set up or is configured to use a database on a host that isn't resolvable (i.e a postgres host that's only resolvable within docker-compose). If you run makemigrations on such a machine it will fail while attempting to check the migrations consistency, which is quite annoying. The solution seems to either add a django.db.backends.dummy backend for such cases or start a database server locally.

I'd like to add a flag to skip the consistency check in these situations, or fail gracefully if the connection to the database isn't available.

[Carlton Gibson]

OK, this seems reasonable to me. (Others can shout if I missed something. :)

[wtkm11]

I added the --skip-consistency-check flag to allow skipping the inconsistent migration history check in the makemigrations command along with a unit test in tests.migrations.test_commands::MakeMigrationsTests.

[wtkm11]

​https://github.com/django/django/pull/12796

[Tom Forbes]

I've been thinking more about this - wouldn't it be preferable to gracefully fail if the check_consistent_history() method fails due to a connection error? Not sure what anyone else thinks, but your MR looks simple enough. Just make sure you add something to the release notes + documentation.

[Mariusz Felisiak]

I agree with Tom, this is quite niche so I would also prefer to fail gracefully. IMO we don't need a new option.

[wtkm11]

I updated the PR so that a CommandError describing the error that was encountered in check_consistent_history will be raised.

[wtkm11]

I just updated the PR again so that a warning describing the error that was encountered in check_consistent_history will be issued (and the command will be able to continue).

[Mariusz Felisiak <felisiak.mariusz@…>]

In 9756c334:

Fixed #31504 -- Allowed calling makemigrations without an active database connection.