Fixed #23408 -- Added migrations questioner prompt for adding unique fields with a callable default.

django/db/migrations/autodetector.py

@@ -880,6 +880,12 @@ class MigrationAutodetector:
                 field.default = self.questioner.ask_auto_now_add_addition(field_name, model_name)
             else:
                 field.default = self.questioner.ask_not_null_addition(field_name, model_name)
+        if (
+            field.unique and
+            field.default is not models.NOT_PROVIDED and
+            callable(field.default)
+        ):
+            self.questioner.ask_unique_callable_default_addition(field_name, model_name)
         self.add_operation(
             app_label,
             operations.AddField(

django/db/migrations/questioner.py

@@ -6,6 +6,7 @@ import sys
 from django.apps import apps
 from django.db.models import NOT_PROVIDED
 from django.utils import timezone
+from django.utils.version import get_docs_version
 
 from .loader import MigrationLoader
 
@@ -79,6 +80,11 @@ class MigrationQuestioner:
         # None means quit
         return None
 
+    def ask_unique_callable_default_addition(self, field_name, model_name):
+        """Adding a unique field with a callable default."""
+        # None means continue.
+        return None
+
 
 class InteractiveMigrationQuestioner(MigrationQuestioner):
 
@@ -229,6 +235,27 @@ class InteractiveMigrationQuestioner(MigrationQuestioner):
                 return self._ask_default(default='timezone.now')
         return None
 
+    def ask_unique_callable_default_addition(self, field_name, model_name):
+        """Adding a unique field with a callable default."""
+        if not self.dry_run:
+            version = get_docs_version()
+            choice = self._choice_input(
+                f'Callable default on unique field {model_name}.{field_name} '
+                f'will not generate unique values upon migrating.\n'
+                f'Please choose how to proceed:\n',
+                [
+                    f'Continue making this migration as the first step in '
+                    f'writing a manual migration to generate unique values '
+                    f'described here: '
+                    f'https://docs.djangoproject.com/en/{version}/howto/'
+                    f'writing-migrations/#migrations-that-add-unique-fields.',
+                    'Quit and edit field options in models.py.',
+                ],
+            )
+            if choice == 2:
+                sys.exit(3)
+        return None
+
 
 class NonInteractiveMigrationQuestioner(MigrationQuestioner):
 

tests/migrations/test_commands.py

@@ -17,6 +17,8 @@ from django.db.migrations.exceptions import InconsistentMigrationHistory
 from django.db.migrations.recorder import MigrationRecorder
 from django.test import TestCase, override_settings, skipUnlessDBFeature
 from django.test.utils import captured_stdout
+from django.utils import timezone
+from django.utils.version import get_docs_version
 
 from .models import UnicodeModel, UnserializableModel
 from .routers import TestRouter
@@ -1870,6 +1872,57 @@ class MakeMigrationsTests(MigrationTestBase):
                 with self.assertRaises(SystemExit):
                     call_command('makemigrations', 'migrations', interactive=True)
 
+    def test_makemigrations_interactive_unique_callable_default_addition(self):
+        """
+        makemigrations prompts the user when adding a unique field with
+        a callable default.
+        """
+        class Book(models.Model):
+            created = models.DateTimeField(unique=True, default=timezone.now)
+
+            class Meta:
+                app_label = 'migrations'
+
+        version = get_docs_version()
+        input_msg = (
+            f'Callable default on unique field book.created will not generate '
+            f'unique values upon migrating.\n'
+            f'Please choose how to proceed:\n\n'
+            f' 1) Continue making this migration as the first step in writing '
+            f'a manual migration to generate unique values described here: '
+            f'https://docs.djangoproject.com/en/{version}/howto/'
+            f'writing-migrations/#migrations-that-add-unique-fields.\n'
+            f' 2) Quit and edit field options in models.py.\n'
+        )
+        with self.temporary_migration_module(module='migrations.test_migrations'):
+            # 2 - quit.
+            with mock.patch('builtins.input', return_value='2'):
+                with captured_stdout() as out, self.assertRaises(SystemExit):
+                    call_command('makemigrations', 'migrations', interactive=True)
+            out_value = out.getvalue()
+            self.assertIn(input_msg, out_value)
+            self.assertNotIn('Add field created to book', out_value)
+            # 1 - continue.
+            with mock.patch('builtins.input', return_value='1'):
+                with captured_stdout() as out:
+                    call_command('makemigrations', 'migrations', interactive=True)
+            out_value = out.getvalue()
+            self.assertIn(input_msg, out_value)
+            self.assertIn('Add field created to book', out_value)
+
+    def test_makemigrations_non_interactive_unique_callable_default_addition(self):
+        class Book(models.Model):
+            created = models.DateTimeField(unique=True, default=timezone.now)
+
+            class Meta:
+                app_label = 'migrations'
+
+        with self.temporary_migration_module(module='migrations.test_migrations'):
+            with captured_stdout() as out:
+                call_command('makemigrations', 'migrations', interactive=False)
+            out_value = out.getvalue()
+            self.assertIn('Add field created to book', out_value)
+
 
 class SquashMigrationsTests(MigrationTestBase):
     """