Fix #5 Prevent MigrationAutoDetector removes the user unique email constraint

[trottomv]

Prevent MigrationAutoDetector removes the user unique email constraint.

After various tests and checks, it seems to me that the control on the presence of migration is a bit redundant and, indeed, could create other problems. So, I limited myself to adding a test and uncommenting the already existing line that acts on original_attrs["constraint"] without introducing the hypothesized control. Am I missing something?
Because it should be enough that "unique_user_email" is in the INSTALLED_APPS and avoid checking the presence of migrations.

[carltongibson]

I think that this will cause the auto-detector to create an auth migration when unique_user_email is installed but the migration is not run. ( maybe it won't... — I put this together interactively, so maybe the end result isn't the same as the half-way point…)

The comment you removed here was part of the longer comment beginning on ln12.

I think we should have tests for both that case and the issue here (which is that an auth migration is created after the unique_user_email migration is run).

[carltongibson]

Ah ha! It' looks like it doesn't 🕺

% ./manage.py showmigrations
admin
 [ ] 0001_initial
 [ ] 0002_logentry_remove_auto_add
 [ ] 0003_logentry_add_action_flag_choices
auth
 [ ] 0001_initial
 [ ] 0002_alter_permission_name_max_length
 [ ] 0003_alter_user_email_max_length
 [ ] 0004_alter_user_username_opts
 [ ] 0005_alter_user_last_login_null
 [ ] 0006_require_contenttypes_0002
 [ ] 0007_alter_validators_add_error_messages
 [ ] 0008_alter_user_username_max_length
 [ ] 0009_alter_user_last_name_max_length
 [ ] 0010_alter_group_name_max_length
 [ ] 0011_update_proxy_permissions
 [ ] 0012_alter_user_first_name_max_length
contenttypes
 [ ] 0001_initial
 [ ] 0002_remove_content_type_name
sessions
 [ ] 0001_initial
unique_user_email
 [ ] 0001_initial
% ./manage.py makemigrations auth
No changes detected in app 'auth'

OK, let me have a play over the weekend, and I'll get this out.

Thanks @trottomv 🎁

[trottomv]

for completenes:

(.venv) $ python manage.py showmigrations
admin
 [X] 0001_initial
 [X] 0002_logentry_remove_auto_add
 [X] 0003_logentry_add_action_flag_choices
auth
 [X] 0001_initial
 [X] 0002_alter_permission_name_max_length
 [X] 0003_alter_user_email_max_length
 [X] 0004_alter_user_username_opts
 [X] 0005_alter_user_last_login_null
 [X] 0006_require_contenttypes_0002
 [X] 0007_alter_validators_add_error_messages
 [X] 0008_alter_user_username_max_length
 [X] 0009_alter_user_last_name_max_length
 [X] 0010_alter_group_name_max_length
 [X] 0011_update_proxy_permissions
 [X] 0012_alter_user_first_name_max_length
contenttypes
 [X] 0001_initial
 [X] 0002_remove_content_type_name
sessions
 [X] 0001_initial
unique_user_email
 [ ] 0001_initial
(.venv) $ python manage.py makemigrations
No changes detected

[carltongibson]

OK, let's have this. Thanks @trottomv 🎁