From 37fc832a54ad37e75a898a2c8f9ab0820617c4af Mon Sep 17 00:00:00 2001
From: Mariusz Felisiak <felisiak.mariusz@gmail.com>
Date: Thu, 30 Nov 2023 10:10:27 +0100
Subject: [PATCH] Fixed #35006 -- Fixed migrations crash when altering
 Meta.db_table_comment on SQLite.
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Thanks Юрий for the report.

Regression in 78f163a4fb3937aca2e71786fbdd51a0ef39629e.
---
 django/db/backends/base/schema.py    | 15 ++++++++-------
 django/db/backends/sqlite3/schema.py |  2 ++
 docs/releases/4.2.8.txt              |  3 +++
 tests/schema/tests.py                | 17 +++++++++++++++++
 4 files changed, 30 insertions(+), 7 deletions(-)

diff --git a/django/db/backends/base/schema.py b/django/db/backends/base/schema.py
index ef859907de8c..aeb3cde9a4df 100644
--- a/django/db/backends/base/schema.py
+++ b/django/db/backends/base/schema.py
@@ -670,13 +670,14 @@ 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."""
diff --git a/django/db/backends/sqlite3/schema.py b/django/db/backends/sqlite3/schema.py
index 64cf0188d2bc..d27a8bbd65d7 100644
--- a/django/db/backends/sqlite3/schema.py
+++ b/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
diff --git a/docs/releases/4.2.8.txt b/docs/releases/4.2.8.txt
index 0550e026bb64..1cce9030ec37 100644
--- a/docs/releases/4.2.8.txt
+++ b/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`).
diff --git a/tests/schema/tests.py b/tests/schema/tests.py
index 46d16e9fdb6b..d1d18bab176d 100644
--- a/tests/schema/tests.py
+++ b/tests/schema/tests.py
@@ -4741,6 +4741,23 @@ 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):