Fixed #33670 -- Fixed altering primary key on SQLite.

django/db/backends/sqlite3/schema.py

@@ -217,7 +217,12 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
             alter_field and getattr(alter_field[1], "primary_key", False)
         ):
             for name, field in list(body.items()):
-                if field.primary_key:
+                if field.primary_key and not (
+                    # Do not remove the old primary key when an altered field
+                    # that introduces a primary key is the same field.
+                    alter_field
+                    and name == alter_field[1].name
+                ):
                     field.primary_key = False
                     restore_pk_field = field
                     if field.auto_created:

tests/schema/tests.py

@@ -3584,6 +3584,21 @@ class SchemaTests(TransactionTestCase):
         )
         self.assertEqual(self.get_primary_key(Tag._meta.db_table), "slug")
 
+    def test_alter_primary_key_the_same_name(self):
+        with connection.schema_editor() as editor:
+            editor.create_model(Thing)
+
+        old_field = Thing._meta.get_field("when")
+        new_field = CharField(max_length=2, primary_key=True)
+        new_field.set_attributes_from_name("when")
+        new_field.model = Thing
+        with connection.schema_editor() as editor:
+            editor.alter_field(Thing, old_field, new_field, strict=True)
+        self.assertEqual(self.get_primary_key(Thing._meta.db_table), "when")
+        with connection.schema_editor() as editor:
+            editor.alter_field(Thing, new_field, old_field, strict=True)
+        self.assertEqual(self.get_primary_key(Thing._meta.db_table), "when")
+
     def test_context_manager_exit(self):
         """
         Ensures transaction is correctly closed when an error occurs