Fixed #35162 -- Fixed crash when adding fields with db_default on MySQL.

MySQL doesn't allow literal DEFAULT values to be used for BLOB, TEXT,
GEOMETRY or JSON columns and requires expression to be used instead.

Regression in 7414704e88d73dafbcfbb85f9bc54cb6111439d3.

django/db/backends/base/schema.py

@@ -412,7 +412,11 @@ class BaseDatabaseSchemaEditor:
         """Return the sql and params for the field's database default."""
         from django.db.models.expressions import Value
 
-        sql = "%s" if isinstance(field.db_default, Value) else "(%s)"
+        sql = (
+            self._column_default_sql(field)
+            if isinstance(field.db_default, Value)
+            else "(%s)"
+        )
         query = Query(model=field.model)
         compiler = query.get_compiler(connection=self.connection)
         default_sql, params = compiler.compile(field.db_default)

docs/releases/5.0.2.txt

@@ -32,3 +32,7 @@ Bugfixes
 * Fixed a regression in Django 5.0 that caused the ``request_finished`` signal to
   sometimes not be fired when running Django through an ASGI server, resulting
   in potential resource leaks (:ticket:`35059`).
+
+* Fixed a bug in Django 5.0 that caused a migration crash on MySQL when adding
+  a ``BinaryField``, ``TextField``, ``JSONField``, or ``GeometryField`` with a
+  ``db_default`` (:ticket:`35162`).

tests/schema/tests.py

@@ -2303,6 +2303,19 @@ class SchemaTests(TransactionTestCase):
         columns = self.column_classes(Author)
         self.assertEqual(columns["birth_year"][1].default, "1988")
 
+    @isolate_apps("schema")
+    def test_add_text_field_with_db_default(self):
+        class Author(Model):
+            description = TextField(db_default="(missing)")
+
+            class Meta:
+                app_label = "schema"
+
+        with connection.schema_editor() as editor:
+            editor.create_model(Author)
+        columns = self.column_classes(Author)
+        self.assertIn("(missing)", columns["description"][1].default)
+
     @skipUnlessDBFeature(
         "supports_column_check_constraints", "can_introspect_check_constraints"
     )