[5.0.x] Fixed #35006 -- Fixed migrations crash when altering Meta.db_…

…table_comment on SQLite.

Thanks Юрий for the report.

Regression in 78f163a.
Backport of 37fc832 from main

django/db/backends/base/schema.py

@@ -671,13 +671,14 @@ def alter_db_table(self, model, old_db_table, new_db_table):
                 sql.rename_table_references(old_db_table, new_db_table)
 
     def alter_db_table_comment(self, model, old_db_table_comment, new_db_table_comment):
-        self.execute(
-            self.sql_alter_table_comment
-            % {
-                "table": self.quote_name(model._meta.db_table),
-                "comment": self.quote_value(new_db_table_comment or ""),
-            }
-        )
+        if self.sql_alter_table_comment and self.connection.features.supports_comments:
+            self.execute(
+                self.sql_alter_table_comment
+                % {
+                    "table": self.quote_name(model._meta.db_table),
+                    "comment": self.quote_value(new_db_table_comment or ""),
+                }
+            )
 
     def alter_db_tablespace(self, model, old_db_tablespace, new_db_tablespace):
         """Move a model's table between tablespaces."""

django/db/backends/sqlite3/schema.py

@@ -19,6 +19,8 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
     sql_delete_column = "ALTER TABLE %(table)s DROP COLUMN %(column)s"
     sql_create_unique = "CREATE UNIQUE INDEX %(name)s ON %(table)s (%(columns)s)"
     sql_delete_unique = "DROP INDEX %(name)s"
+    sql_alter_table_comment = None
+    sql_alter_column_comment = None
 
     def __enter__(self):
         # Some SQLite schema alterations need foreign key constraints to be

docs/releases/4.2.8.txt

@@ -35,3 +35,6 @@ Bugfixes
 * Fixed a regression in Django 4.2 where the admin's read-only password widget
   and some help texts were incorrectly aligned at tablet widths
   (:ticket:`34982`).
+
+* Fixed a regression in Django 4.2 that caused a migration crash on SQLite when
+  altering unsupported ``Meta.db_table_comment`` (:ticket:`35006`).

tests/schema/tests.py

@@ -4870,6 +4870,23 @@ class Meta:
             [None, ""],
         )
 
+    @isolate_apps("schema")
+    @skipIfDBFeature("supports_comments")
+    def test_db_comment_table_unsupported(self):
+        class ModelWithDbTableComment(Model):
+            class Meta:
+                app_label = "schema"
+                db_table_comment = "Custom table comment"
+
+        # Table comments are ignored on databases that don't support them.
+        with connection.schema_editor() as editor, self.assertNumQueries(1):
+            editor.create_model(ModelWithDbTableComment)
+        self.isolated_local_models = [ModelWithDbTableComment]
+        with connection.schema_editor() as editor, self.assertNumQueries(0):
+            editor.alter_db_table_comment(
+                ModelWithDbTableComment, "Custom table comment", "New table comment"
+            )
+
     @isolate_apps("schema")
     @skipUnlessDBFeature("supports_comments", "supports_foreign_keys")
     def test_db_comments_from_abstract_model(self):