Fixed #27935 -- Fixed crash with BrinIndex name > 30 characters.

django/contrib/postgres/indexes.py

+from django.db import connection
 from django.db.models import Index
+from django.utils.functional import cached_property
 
 __all__ = ['BrinIndex', 'GinIndex']
 
@@ -34,6 +36,14 @@ class BrinIndex(Index):
                 schema_editor.quote_value(self.pages_per_range)) + parameters['extra']
         return parameters
 
+    @cached_property
+    def max_name_length(self):
+        # Allow an index name longer than 30 characters since the suffix
+        # is 4 characters (usual limit is 3). Since this index can only be
+        # used on PostgreSQL, the 30 character limit for cross-database
+        # compatibility isn't applicable.
+        return connection.ops.max_name_length()
+
 
 class GinIndex(Index):
     suffix = 'gin'

django/db/models/indexes.py

@@ -4,12 +4,12 @@ from django.utils.encoding import force_bytes
 
 __all__ = ['Index']
 
-# The max length of the names of the indexes (restricted to 30 due to Oracle)
-MAX_NAME_LENGTH = 30
-
 
 class Index:
     suffix = 'idx'
+    # The max length of the name of the index (restricted to 30 for
+    # cross-database compatibility with Oracle)
+    max_name_length = 30
 
     def __init__(self, fields=[], name=None):
         if not isinstance(fields, list):
@@ -25,8 +25,8 @@ class Index:
         self.name = name or ''
         if self.name:
             errors = self.check_name()
-            if len(self.name) > MAX_NAME_LENGTH:
-                errors.append('Index names cannot be longer than %s characters.' % MAX_NAME_LENGTH)
+            if len(self.name) > self.max_name_length:
+                errors.append('Index names cannot be longer than %s characters.' % self.max_name_length)
             if errors:
                 raise ValueError(errors)
 
@@ -100,13 +100,15 @@ class Index:
             (('-%s' if order else '%s') % column_name)
             for column_name, (field_name, order) in zip(column_names, self.fields_orders)
         ]
+        # The length of the parts of the name is based on the default max
+        # length of 30 characters.
         hash_data = [table_name] + column_names_with_order + [self.suffix]
         self.name = '%s_%s_%s' % (
             table_name[:11],
             column_names[0][:7],
             '%s_%s' % (self._hash_generator(*hash_data), self.suffix),
         )
-        assert len(self.name) <= MAX_NAME_LENGTH, (
+        assert len(self.name) <= self.max_name_length, (
             'Index too long for multiple database support. Is self.suffix '
             'longer than 3 characters?'
         )

tests/postgres_tests/test_indexes.py

@@ -3,7 +3,7 @@ from django.db import connection
 from django.test import skipUnlessDBFeature
 
 from . import PostgreSQLTestCase
-from .models import CharFieldModel, IntegerArrayModel
+from .models import CharFieldModel, DateTimeArrayModel, IntegerArrayModel
 
 
 @skipUnlessDBFeature('has_brin_index_support')
@@ -23,6 +23,17 @@ class BrinIndexTests(PostgreSQLTestCase):
         index_with_page_range = BrinIndex(fields=['title'], pages_per_range=16)
         self.assertNotEqual(index, index_with_page_range)
 
+    def test_name_auto_generation(self):
+        """
+        A name longer than 30 characters (since len(BrinIndex.suffix) is 4
+        rather than usual limit of 3) is okay for PostgreSQL. For this test,
+        the name of the field ('datetimes') must be at least 7 characters to
+        generate a name longer than 30 characters.
+        """
+        index = BrinIndex(fields=['datetimes'])
+        index.set_name_with_model(DateTimeArrayModel)
+        self.assertEqual(index.name, 'postgres_te_datetim_abf104_brin')
+
     def test_deconstruction(self):
         index = BrinIndex(fields=['title'], name='test_title_brin')
         path, args, kwargs = index.deconstruct()