Django "Ghost Migrations" Issue

You've raised an interesting point about Django's migration system not warning about migrations that exist in the database but are no longer present in the code (what you call "ghost migrations").

Based on the available Django documentation, there isn't a built-in feature specifically addressing this issue in the core framework. However, there are some related features worth noting:

Current Migration Checking in Django

Django 1.7 introduced the built-in schema migrations system, replacing South. The system includes:

• The migrate command which replaced syncdb
• The makemigrations command for detecting model changes
• Various signals and router methods for migration handling

Potential Solution Using Custom Commands

One approach would be to create a custom management command that checks for these ghost migrations. Django's BaseCommand class provides a foundation for this:

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from django.core.management.base import BaseCommand
from django.db.migrations.recorder import MigrationRecorder
from django.db.migrations.loader import MigrationLoader

class Command(BaseCommand):
    help = 'Checks for ghost migrations in the database'

    def handle(self, *args, **options):
        # Get migrations from the database
        recorder = MigrationRecorder(connection)
        applied_migrations = recorder.migration_qs.all()
        
        # Get migrations from the filesystem
        loader = MigrationLoader(connection)
        
        # Check for migrations in DB but not in code
        ghost_migrations = []
        for migration in applied_migrations:
            app_label = migration.app
            name = migration.name
            if (app_label, name) not in loader.disk_migrations:
                ghost_migrations.append((app_label, name))
        
        if ghost_migrations:
            self.stdout.write(self.style.WARNING(
                'Found ghost migrations in the database:'))
            for app, name in ghost_migrations:
                self.stdout.write(f'  {app}.{name}')

Regarding Deprecation Warnings

It's worth noting that Django's approach to warnings has changed over time. In Django 1.11, deprecation warnings were made less prominent by default (no longer displayed), aligning with Python's default behavior. This was done to allow third-party apps to support multiple Django versions without showing excessive warnings.

Migration Checks in Commands

Django does have a requires_migrations_checks attribute for BaseCommand that, when set to True, will warn about migration mismatches between disk and database. However, based on the documentation, this appears to focus on unapplied migrations rather than ghost migrations:

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class Command(BaseCommand):
    requires_migrations_checks = True
    # rest of command implementation

Conclusion

Your suggestion to implement a ghost migration check seems reasonable and could be valuable to the Django community. Since this isn't currently part of Django's core functionality, you might consider:

1. Creating a standalone package that provides this functionality
2. Submitting a feature proposal to the Django project
3. Implementing it as a custom management command for your own projects

The approach of scanning the migrations table for entries that don't exist in the code is conceptually sound, though as you noted, there would be complexities around uninstalled apps and squashed migrations.