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

2 files changed, 33 insertions, 0 deletions

diff --git a/django/db/migrations/autodetector.py b/django/db/migrations/autodetector.py
index 594658ce99..3276320a1e 100644
--- a/django/db/migrations/autodetector.py
+++ b/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(
diff --git a/django/db/migrations/questioner.py b/django/db/migrations/questioner.py
index 3891616ce0..349e35130e 100644
--- a/django/db/migrations/questioner.py
+++ b/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):