[Django] #28803: When renaming foreign key indexes don't get renamed which breaks next migrations

[Django]

#28803: When renaming foreign key indexes don't get renamed which breaks next
migrations
-----------------------------------------+------------------------
               Reporter:  Jacek Bzdak    |          Owner:  nobody
                   Type:  Uncategorized  |         Status:  new
              Component:  Migrations     |        Version:  1.11
               Severity:  Normal         |       Keywords:
           Triage Stage:  Unreviewed     |      Has patch:  0
    Needs documentation:  0              |    Needs tests:  0
Patch needs improvement:  0              |  Easy pickings:  0
                  UI/UX:  0              |
-----------------------------------------+------------------------
 Here is what I did. I have following models:

 {{{
 class ReferencedModel(models.Model):
    pass


 class SecondReferencedModel(models.Model):
    pass


 class ReferenceeModel(models.Model):
   child = models.ForeignKey(ReferencedModel, default=None,
 on_delete=models.CASCADE)
 }}}

 I want to swichch ``ReferenceeModel.child`` to ``SecondReferencedModel``.

 I want to do it by:

 1) Renaming ``ReferenceeModel.child_old``
 2) Adding ``ReferenceeModel.child`` that points to proper model
 3) Some RunPython magic
 4) Delete  ``ReferenceeModel.child_old``

 Actual bug:

 {{{

 class Migration(migrations.Migration):

     initial = True

     dependencies = [
     ]

     operations = [
         migrations.CreateModel(
             name='ReferencedModel',
             fields=[
                 ('id', models.AutoField(auto_created=True,
 primary_key=True, serialize=False, verbose_name='ID')),
             ],
         ),
         migrations.CreateModel(
             name='SecondReferencedModel',
             fields=[
                 ('id', models.AutoField(auto_created=True,
 primary_key=True, serialize=False, verbose_name='ID')),
             ],
         ),
         migrations.CreateModel(
             name='ReferenceeModel',
             fields=[
                 ('id', models.AutoField(auto_created=True,
 primary_key=True, serialize=False, verbose_name='ID')),
                 ('child',
 models.ForeignKey(on_delete=django.db.models.deletion.CASCADE,
 to='index_error.ReferencedModel')),
             ],
         ),
     ]

 class Migration(migrations.Migration):

     dependencies = [
         ('index_error', '0001_initial'),
     ]

     operations = [
         migrations.RenameField(
             model_name='referenceemodel',
             old_name='child',
             new_name='child_copy',
         ),
     ]


 class Migration(migrations.Migration):

     dependencies = [
         ('index_error', '0002_auto_20171116_1505'),
     ]

     operations = [
         migrations.AddField(
             model_name='referenceemodel',
             name='child',
             field=models.ForeignKey(default=None,
 on_delete=django.db.models.deletion.CASCADE,
 to='index_error.SecondReferencedModel'),
         ),
     ]

 }}}

 Third migration explodes with following error:

 {{{django.db.utils.ProgrammingError: relation
 "index_error_referenceemodel_child_id_59ba6fc6" already exist }}}

 Which is due to the

 1) Field `` child = models.ForeignKey(ReferencedModel, ...)`` generates
 postgresql index named ``index_error_referenceemodel_child_id_59ba6fc6``
 2) RenameField operation doesn't update index name (but changes field
 name)
 3) When I try to create new field index names clash.

 My setup:

 * Django 1.11 (also broken in 2.0)
 * postgresql database

-- 
Ticket URL: <https://code.djangoproject.com/ticket/28803>
Django <https://code.djangoproject.com/>
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