[1.11.x] Refs #28876 -- Fixed incorrect class-based model index name generation for models with quoted db_table.

Thanks Simon Charette and Tim Graham for the review and Carlos E. C.
Leite for the report.

Backport of f79d9a322c6008e5fada1453aebfb56afc316cc8 from master

django/db/models/indexes.py

@@ -2,6 +2,7 @@ from __future__ import unicode_literals
 
 import hashlib
 
+from django.db.backends.utils import split_identifier
 from django.utils.encoding import force_bytes
 
 __all__ = [str('Index')]
@@ -101,7 +102,7 @@ class Index(object):
         (8 chars) and unique hash + suffix (10 chars). Each part is made to
         fit its size by truncating the excess length.
         """
-        table_name = model._meta.db_table
+        _, table_name = split_identifier(model._meta.db_table)
         column_names = [model._meta.get_field(field_name).column for field_name, order in self.fields_orders]
         column_names_with_order = [
             (('-%s' if order else '%s') % column_name)

docs/releases/1.11.9.txt

@@ -11,3 +11,6 @@ Bugfixes
 
 * Fixed a regression in Django 1.11 that added newlines between ``MultiWidget``'s
   subwidgets (:ticket:`28890`).
+
+* Fixed incorrect class-based model index name generation for models with
+  quoted ``db_table`` (:ticket:`28876`).

tests/model_indexes/tests.py

@@ -1,5 +1,6 @@
 from django.db import models
 from django.test import SimpleTestCase
+from django.test.utils import isolate_apps
 
 from .models import Book, ChildModel1, ChildModel2
 
@@ -69,6 +70,18 @@ class IndexesTests(SimpleTestCase):
         with self.assertRaisesMessage(AssertionError, msg):
             long_field_index.set_name_with_model(Book)
 
+    @isolate_apps('model_indexes')
+    def test_name_auto_generation_with_quoted_db_table(self):
+        class QuotedDbTable(models.Model):
+            name = models.CharField(max_length=50)
+
+            class Meta:
+                db_table = '"t_quoted"'
+
+        index = models.Index(fields=['name'])
+        index.set_name_with_model(QuotedDbTable)
+        self.assertEqual(index.name, 't_quoted_name_e4ed1b_idx')
+
     def test_deconstruction(self):
         index = models.Index(fields=['title'])
         index.set_name_with_model(Book)