Fixed #21497 -- Forced conversion to bytes for very long index names

Author: jbohman

Diff for: AUTHORS

@@ -123,6 +123,7 @@ answer newbie questions, and generally made Django that much better:
     David Blewett <[email protected]>
     Artem Gnilov <[email protected]>
     Eric Boersma <[email protected]>
+    Joel Bohman <[email protected]>
     Matías Bordese
     Nate Bragg <[email protected]>
     Sean Brant

Diff for: django/db/backends/schema.py

@@ -5,6 +5,7 @@
 from django.db.backends.utils import truncate_name
 from django.db.models.fields.related import ManyToManyField
 from django.db.transaction import atomic
+from django.utils.encoding import force_bytes
 from django.utils.log import getLogger
 from django.utils.six.moves import reduce
 from django.utils.six import callable
@@ -703,7 +704,7 @@ def _create_index_name(self, model, column_names, suffix=""):
             index_name = index_name[1:]
         # If it's STILL too long, just hash it down
         if len(index_name) > self.connection.features.max_index_name_length:
-            index_name = hashlib.md5(index_name).hexdigest()[:self.connection.features.max_index_name_length]
+            index_name = hashlib.md5(force_bytes(index_name)).hexdigest()[:self.connection.features.max_index_name_length]
         # It can't start with a number on Oracle, so prepend D if we need to
         if index_name[0].isdigit():
             index_name = "D%s" % index_name[:-1]

Diff for: tests/schema/models.py

@@ -95,3 +95,10 @@ class UniqueTest(models.Model):
     class Meta:
         app_cache = new_app_cache
         unique_together = ["year", "slug"]
+
+
+class BookWithLongName(models.Model):
+    author_foreign_key_with_really_long_field_name = models.ForeignKey(Author)
+
+    class Meta:
+        app_cache = new_app_cache

Diff for: tests/schema/tests.py

@@ -7,7 +7,9 @@
 from django.db.models.fields import IntegerField, TextField, CharField, SlugField
 from django.db.models.fields.related import ManyToManyField, ForeignKey
 from django.db.transaction import atomic
-from .models import Author, AuthorWithM2M, Book, BookWithSlug, BookWithM2M, Tag, TagIndexed, TagM2MTest, TagUniqueRename, UniqueTest
+from .models import (Author, AuthorWithM2M, Book, BookWithLongName,
+    BookWithSlug, BookWithM2M, Tag, TagIndexed, TagM2MTest, TagUniqueRename,
+    UniqueTest)
 
 
 class SchemaTests(TransactionTestCase):
@@ -21,7 +23,10 @@ class SchemaTests(TransactionTestCase):
 
     available_apps = []
 
-    models = [Author, AuthorWithM2M, Book, BookWithSlug, BookWithM2M, Tag, TagIndexed, TagM2MTest, TagUniqueRename, UniqueTest]
+    models = [
+        Author, AuthorWithM2M, Book, BookWithLongName, BookWithSlug,
+        BookWithM2M, Tag, TagIndexed, TagM2MTest, TagUniqueRename, UniqueTest,
+    ]
 
     # Utility functions
 
@@ -659,3 +664,18 @@ class SomeError(Exception):
                 raise SomeError
         except SomeError:
             self.assertFalse(connection.in_atomic_block)
+
+    def test_foreign_key_index_long_names_regression(self):
+        """
+        Regression test for #21497. Only affects databases that supports
+        foreign keys.
+        """
+        # Create the table
+        with connection.schema_editor() as editor:
+            editor.create_model(Author)
+            editor.create_model(BookWithLongName)
+        # Ensure the table is there and has the right index
+        self.assertIn(
+            "author_foreign_key_with_really_long_field_name_id",
+            connection.introspection.get_indexes(connection.cursor(), BookWithLongName._meta.db_table),
+        )