Add a test that checks for missing migrations

If there are any outstanding model changes that have no migrations, the
tests will fail. Migrations *must* be up-to-date before any code changes
are accepted, or before a new version is released. If they are not, it
causes havoc for all users.

The bulk of the test code is taken from the Django 1.7 `makemigrations`
command, and the South `schemamigration` command.

wagtail/wagtailcore/tests/test_migrations.py

@@ -0,0 +1,121 @@
+"""
+Check that all changes to Wagtail models have had migrations created. If there
+are outstanding model changes that need migrations, fail the tests.
+"""
+
+from django import VERSION
+from django.test import TransactionTestCase
+
+from django.utils.six import iteritems
+import south.management.commands.schemamigration
+
+try:
+    from unittest import skipIf, skipUnless
+except ImportError:
+    from django.utils.unittest import skipIf, skipUnless
+
+
+class TestForMigrations(TransactionTestCase):
+
+    @skipIf(VERSION < (1, 7), "Migrations introduced in Django 1.7")
+    def test_django_17_migrations(self):
+
+        from django.apps import apps
+        from django.db.migrations.loader import MigrationLoader
+        from django.db.migrations.autodetector import MigrationAutodetector
+        from django.db.migrations.state import ProjectState
+        from django.db.migrations.questioner import MigrationQuestioner
+        app_labels = set(app.label for app in apps.get_app_configs()
+                         if app.name.startswith('wagtail.'))
+        for app_label in app_labels:
+            apps.get_app_config(app_label.split('.')[-1])
+        loader = MigrationLoader(None, ignore_no_migrations=True)
+
+        conflicts = dict(
+            (app_label, conflict)
+            for app_label, conflict in iteritems(loader.detect_conflicts())
+            if app_label in app_labels
+        )
+
+        if conflicts:
+            name_str = "; ".join("%s in %s" % (", ".join(names), app)
+                                 for app, names in conflicts.items())
+            self.fail("Conflicting migrations detected (%s)." % name_str)
+
+        autodetector = MigrationAutodetector(
+            loader.project_state(),
+            ProjectState.from_apps(apps),
+            MigrationQuestioner(specified_apps=app_labels, dry_run=True),
+        )
+
+        changes = autodetector.changes(
+            graph=loader.graph,
+            trim_to_apps=app_labels or None,
+            convert_apps=app_labels or None,
+        )
+
+        if changes:
+            apps = ', '.join(apps.get_app_config(label).name
+                             for label in changes.keys())
+            self.fail('Model changes with no migrations detected in apps: %s' % (apps,))
+
+    @skipUnless(VERSION < (1, 7), "South migrations used for Django < 1.7")
+    def test_south_migrations(self):
+
+        from django.core.exceptions import ImproperlyConfigured
+        from django.conf import settings
+        from django.db import models
+
+        from south.migration import Migrations, migrate_app
+        from south.models import MigrationHistory
+        from south.exceptions import NoMigrations
+        from south.creator import changes, actions, freezer
+        from south.management.commands.datamigration import Command as DataCommand
+
+        apps = [app for app in settings.INSTALLED_APPS
+                if app.startswith('wagtail.')]
+        failing_apps = []
+        for app_name in apps:
+            app = app_name.split('.')[-1]
+            try:
+                models.get_app(app)
+            except ImproperlyConfigured:
+                # This module fails to load, probably because it has no
+                # models.py. Ignore it and move on
+                continue
+
+            try:
+                migrations = Migrations(app, force_creation=False, verbose_creation=False)
+                last_migration = migrations[-1]
+            except (NoMigrations, IndexError):
+                # No migrations for this app, probably doesnt have models
+                continue
+
+            if migrations.app_label() not in getattr(last_migration.migration_class(), "complete_apps", []):
+                self.fail("Automatic migrations checking failed, since the previous migration does not have this whole app frozen.\nEither make migrations using '--freeze %s' or set 'SOUTH_AUTO_FREEZE_APP = True' in your settings.py." % migrations.app_label())
+
+            # Alright, construct two model dicts to run the differ on.
+            old_defs = dict(
+                (k, v) for k, v in last_migration.migration_class().models.items()
+                if k.split(".")[0] == migrations.app_label()
+            )
+            new_defs = dict(
+                (k, v) for k, v in freezer.freeze_apps([migrations.app_label()]).items()
+                if k.split(".")[0] == migrations.app_label()
+            )
+            change_source = changes.AutoChanges(
+                migrations = migrations,
+                old_defs = old_defs,
+                old_orm = last_migration.orm(),
+                new_defs = new_defs,
+            )
+
+            name = 'test'
+
+            # Get the actions, and then insert them into the actions lists
+            if list(change_source.get_changes()):
+                failing_apps.append(app_name)
+
+        if failing_apps:
+            self.fail('Model changes with no South migration detected in apps: %s' % (
+                ', '.join(failing_apps)))