GeneratedField alteration fail on SQLite due table remake data insertion

[Moshe Dicker]

A migration where I added an index to a generated column resulted in a migrations that fails with

django.db.utils.OperationalError: cannot INSERT into generated column "effectivePrice"

[Simon Charette]

Thank you for your report, a traceback and a description of the backend you are using would have been appreciated.

This looks like a problem isolated to SQLite due to the way _remake_table doesn't exclude generated fields from its INSERT INTO new_table SELECT ... FROM old_table at table rename time (a necessary step since SQLite doesn't support most table alterations).

django/db/backends/sqlite3/schema.py

@@ -150 +150 @@
             body.pop(old_field.name, None)
             mapping.pop(old_field.column, None)
             body[new_field.name] = new_field
-            if old_field.null and not new_field.null:
+            if new_field.generated:
+                pass
+            elif old_field.null and not new_field.null:
                 if new_field.db_default is NOT_PROVIDED:
                     default = self.prepare_default(self.effective_default(new_field))
                 else:

[Sarah Boyce <42296566+sarahboyce@…>]

In d048f0d:

Fixed #35373 -- Fixed a crash when indexing a generated field on SQLite.

Generated fields have to be excluded from the INSERT query against the remade
table including the index.

Thanks Moshe Dicker for the report, David Sanders and Mariusz Felisiak for the
review.

[Sarah Boyce <42296566+sarahboyce@…>]

In 9d79714:

[5.0.x] Fixed #35373 -- Fixed a crash when indexing a generated field on SQLite.

Generated fields have to be excluded from the INSERT query against the remade
table including the index.

Thanks Moshe Dicker for the report, David Sanders and Mariusz Felisiak for the
review.

Backport of d048f0d311cc9cb9578d687968f2d24a0a9efddb from main.