Fixed #32350 -- Fixed showmigrations crash for applied squashed migrations.

[danielebra]

https://code.djangoproject.com/ticket/32350#ticket

Some migrations don't have an applied timestamp, this pull requests ensures a check takes place before attempting to show it.

[charettes]

Thanks for the adjustments @danielebra!

Per the documentation if replaces is used then the replaced migrations should still be around

You must then transition the squashed migration to a normal migration by:

• Deleting all the migration files it replaces.
• Updating all migrations that depend on the deleted migrations to depend on the squashed migration instead.
• Removing the replaces attribute in the Migration class of the squashed migration (this is how Django tells that it is a squashed migration).

So I'd add test_migrations_initial_squash/0001_initial.py and test_migrations_initial_squash/0002_replaced.py as well. I managed to reproduce even with these files around but at least we're sure not to test an unsupported setup.

I'll submit a PR to deal with the Running (pre/post)-migrate handlers for application migrations messages during test runs.

[danielebra]

Thanks for the feedback @charettes, apologies for the late reply.

I have added in the first and second migration steps. Please review when convenient.

[charettes]

Beyond the stylistic adjustments this LGTM. Thanks for the patch @danielebra!

[felixxm]

@danielebra Thanks for this patch 👍 Welcome aboard ⛵

I pushed small edits to tests and reused an existing set of migrations test_migrations_squashed.