[3.2.x] Fixed #32832 -- Fixed adding BLOB/TEXT nullable field with de…

…fault on MySQL 8.0.13+.

Regression in d4ac23b.

Thanks Omkar Deshpande for the report.

Backport of fa0433d from main

django/db/backends/base/schema.py

@@ -225,7 +225,14 @@ def column_sql(self, model, field, include_default=False):
         # Work out nullability
         null = field.null
         # If we were told to include a default value, do so
-        include_default = include_default and not self.skip_default(field)
+        include_default = (
+            include_default and
+            not self.skip_default(field) and
+            # Don't include a default value if it's a nullable field and the
+            # default cannot be dropped in the ALTER COLUMN statement (e.g.
+            # MySQL longtext and longblob).
+            not (null and self.skip_default_on_alter(field))
+        )
         if include_default:
             default_value = self.effective_default(field)
             column_default = ' DEFAULT ' + self._column_default_sql(field)
@@ -515,7 +522,7 @@ def add_field(self, model, field):
         self.execute(sql, params)
         # Drop the default if we need to
         # (Django usually does not use in-database defaults)
-        if not self.skip_default(field) and self.effective_default(field) is not None:
+        if not self.skip_default_on_alter(field) and self.effective_default(field) is not None:
             changes_sql, params = self._alter_column_default_sql(model, None, field, drop=True)
             sql = self.sql_alter_column % {
                 "table": self.quote_name(model._meta.db_table),

docs/releases/3.2.5.txt

@@ -16,3 +16,7 @@ Bugfixes
 * Fixed a bug in Django 3.2 that caused a migration crash on MySQL 8.0.13+ when
   altering ``BinaryField``, ``JSONField``, or ``TextField`` to non-nullable
   (:ticket:`32503`).
+
+* Fixed a regression in Django 3.2 that caused a migration crash on MySQL
+  8.0.13+ when adding nullable ``BinaryField``, ``JSONField``, or ``TextField``
+  with a default value (:ticket:`32832`).

tests/schema/tests.py

@@ -3131,6 +3131,33 @@ def test_add_field_default_nullable(self):
             if connection.features.can_introspect_default:
                 self.assertIn(field.default, ['NULL', None])
 
+    def test_add_textfield_default_nullable(self):
+        with connection.schema_editor() as editor:
+            editor.create_model(Author)
+        # Add new nullable TextField with a default.
+        new_field = TextField(blank=True, null=True, default='text')
+        new_field.set_attributes_from_name('description')
+        with connection.schema_editor() as editor:
+            editor.add_field(Author, new_field)
+        Author.objects.create(name='Anonymous1')
+        with connection.cursor() as cursor:
+            cursor.execute('SELECT description FROM schema_author;')
+            item = cursor.fetchall()[0]
+            self.assertIsNone(item[0])
+            field = next(
+                f
+                for f in connection.introspection.get_table_description(
+                    cursor,
+                    'schema_author',
+                )
+                if f.name == 'description'
+            )
+            # Field is still nullable.
+            self.assertTrue(field.null_ok)
+            # The database default is no longer set.
+            if connection.features.can_introspect_default:
+                self.assertIn(field.default, ['NULL', None])
+
     def test_alter_field_default_dropped(self):
         # Create the table
         with connection.schema_editor() as editor: