Showmigrations applied timestamp can cause runtime error

[Daniel Ebrahimian]

The functionality of showmigrations --verbosity 2 will show the applied timestamps for migrations.

In certain scenarios, a timestamp isn't available and will cause a run time error of

AttributeError: 'Migration' object has no attribute 'applied'.

An example of this is having social_django migrations in a project.

Proposed solution: Safely check for the applied timestamp to exist before logging it.

Current workaround: Don't use --verbosity 2

Logs

This shows the type for the applied_migration

<class 'django.db.migrations.recorder.MigrationRecorder.Migration.<locals>.Migration'>
 [X] 0045_auto_20201125_0810 (applied at 2021-01-13 23:39:40)
<class 'django.db.migrations.recorder.MigrationRecorder.Migration.<locals>.Migration'>
 [X] 0046_auto_20201218_0440 (applied at 2021-01-13 23:39:42)
sessions
<class 'django.db.migrations.recorder.MigrationRecorder.Migration.<locals>.Migration'>
 [X] 0001_initial (applied at 2021-01-13 23:40:46)
social_django
<class 'social_django.migrations.0001_initial.Migration'>
Traceback (most recent call last):
  File "real_manage.py", line 23, in <module>
    execute_from_command_line(sys.argv)
  File "/usr/local/lib/python3.8/site-packages/django/core/management/__init__.py", line 401, in execute_from_command_line
    utility.execute()
  File "/usr/local/lib/python3.8/site-packages/django/core/management/__init__.py", line 395, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/local/lib/python3.8/site-packages/django/core/management/base.py", line 328, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/usr/local/lib/python3.8/site-packages/django/core/management/base.py", line 369, in execute
    output = self.handle(*args, **options)
  File "/usr/local/lib/python3.8/site-packages/django/core/management/commands/showmigrations.py", line 52, in handle
    return self.show_list(connection, options['app_label'])
  File "/usr/local/lib/python3.8/site-packages/django/core/management/commands/showmigrations.py", line 97, in show_list
    output += ' (applied at %s)' % applied_migration.applied.strftime('%Y-%m-%d %H:%M:%S')
AttributeError: 'Migration' object has no attribute 'applied'

This is after the proposed pull request

 [X] 0045_auto_20201125_0810 (applied at 2021-01-13 23:39:40)
<class 'django.db.migrations.recorder.MigrationRecorder.Migration.<locals>.Migration'>
 [X] 0046_auto_20201218_0440 (applied at 2021-01-13 23:39:42)
sessions
<class 'django.db.migrations.recorder.MigrationRecorder.Migration.<locals>.Migration'>
 [X] 0001_initial (applied at 2021-01-13 23:40:46)
social_django
<class 'social_django.migrations.0001_initial.Migration'>
 [X] 0001_initial (2 squashed migrations)
<class 'social_django.migrations.0002_add_related_name.Migration'>
 [X] 0002_add_related_name (2 squashed migrations)

​https://github.com/django/django/pull/13890