Fixed #33246 -- Made squashmigrations raise CommandError when squashed_name already exists.

2 files changed, 15 insertions, 0 deletions

diff --git a/django/core/management/commands/squashmigrations.py b/django/core/management/commands/squashmigrations.py
index 65da95a19b..80fdc0cbc1 100644
--- a/django/core/management/commands/squashmigrations.py
+++ b/django/core/management/commands/squashmigrations.py
@@ -1,3 +1,5 @@
+import os
+
 from django.apps import apps
 from django.conf import settings
 from django.core.management.base import BaseCommand, CommandError
@@ -184,6 +186,10 @@ class Command(BaseCommand):
 
         # Write out the new migration file
         writer = MigrationWriter(new_migration, include_header)
+        if os.path.exists(writer.path):
+            raise CommandError(
+                f'Migration {new_migration.name} already exists. Use a different name.'
+            )
         with open(writer.path, "w", encoding='utf-8') as fh:
             fh.write(writer.as_string())
 
diff --git a/tests/migrations/test_commands.py b/tests/migrations/test_commands.py
index 02e2a1ee11..9755af9f6d 100644
--- a/tests/migrations/test_commands.py
+++ b/tests/migrations/test_commands.py
@@ -2082,6 +2082,15 @@ class SquashMigrationsTests(MigrationTestBase):
             squashed_migration_file = os.path.join(migration_dir, '0001_%s.py' % squashed_name)
             self.assertTrue(os.path.exists(squashed_migration_file))
 
+    def test_squashed_name_exists(self):
+        msg = 'Migration 0001_initial already exists. Use a different name.'
+        with self.temporary_migration_module(module='migrations.test_migrations'):
+            with self.assertRaisesMessage(CommandError, msg):
+                call_command(
+                    'squashmigrations', 'migrations', '0001', '0002',
+                    squashed_name='initial', interactive=False, verbosity=0,
+                )
+
 
 class AppLabelErrorTests(TestCase):
     """