Postgres 16.2 with _iexact leads to psycopg2.errors.IndeterminateCollation

[Aldalen]

There is something up with how "_iexact" GeneratedField expressions are turned into SQL for postgres 16.2. This does not occur with 16.1. This leads to a "psycopg2.errors.IndeterminateCollation: could not determine which collation to use for upper() function" error. This was caught in our CI/CD env when I revved it to 16.2. Existing / old migrations failed. This is a reduced examples from our code, with exception paths redacted where necessary.

Model Definition:

class TestModel(models.Model):
     test = models.CharField(max_length=254, blank=True)
     test_gen = models.GeneratedField(expression=models.Q(test__iexact='yes'), output_field=models.BooleanField(), db_persist=True)

Migration content:

migrations.AddField(
            model_name='testmodel',
            name='test_gen',
            field=models.GeneratedField(db_persist=True, expression=models.Q(("test__iexact",'yes')), output_field=models.BooleanField()),
        )

Error:

  Applying module.migration_name...Traceback (most recent call last):
  File "/opt/venv/lib/python3.11/site-packages/django/db/backends/utils.py", line 103, in _execute
    return self.cursor.execute(sql)
           ^^^^^^^^^^^^^^^^^^^^^^^^
psycopg2.errors.IndeterminateCollation: could not determine which collation to use for upper() function
HINT:  Use the COLLATE clause to set the collation explicitly.
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
  File "/builds/[redacted]/manage.py", line 15, in <module>
    execute_from_command_line(sys.argv)
  File "/opt/[redacted]/lib/python3.11/site-packages/django/core/management/__init__.py", line 442, in execute_from_command_line
    utility.execute()
  File "/opt/[redacted]/lib/python3.11/site-packages/django/core/management/__init__.py", line 436, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/opt/[redacted]/lib/python3.11/site-packages/django/core/management/base.py", line 413, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/opt/[redacted]/lib/python3.11/site-packages/django/core/management/base.py", line 459, in execute
    output = self.handle(*args, **options)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/[redacted]/lib/python3.11/site-packages/django/core/management/base.py", line 107, in wrapper
    res = handle_func(*args, **kwargs)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/[redacted]/lib/python3.11/site-packages/django/core/management/commands/migrate.py", line 356, in handle
    post_migrate_state = executor.migrate(
                         ^^^^^^^^^^^^^^^^^
  File "/opt/[redacted]/lib/python3.11/site-packages/django/db/migrations/executor.py", line 135, in migrate
    state = self._migrate_all_forwards(
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/[redacted]/lib/python3.11/site-packages/django/db/migrations/executor.py", line 167, in _migrate_all_forwards
    state = self.apply_migration(
            ^^^^^^^^^^^^^^^^^^^^^
  File "/opt/[redacted]/lib/python3.11/site-packages/django/db/migrations/executor.py", line 252, in apply_migration
    state = migration.apply(state, schema_editor)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/[redacted]/lib/python3.11/site-packages/django/db/migrations/migration.py", line 132, in apply
    operation.database_forwards(
  File "/opt/[redacted]/lib/python3.11/site-packages/django/db/migrations/operations/fields.py", line 108, in database_forwards
    schema_editor.add_field(
  File "/opt/[redacted]/lib/python3.11/site-packages/django/db/backends/base/schema.py", line 750, in add_field
    self.execute(sql, params)
  File "/opt/[redacted]/lib/python3.11/site-packages/django/db/backends/postgresql/schema.py", line 48, in execute
    return super().execute(sql, None)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/[redacted]/lib/python3.11/site-packages/django/db/backends/base/schema.py", line 201, in execute
    cursor.execute(sql, params)
  File "/opt/[redacted]/lib/python3.11/site-packages/django/db/backends/utils.py", line 122, in execute
    return super().execute(sql, params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/[redacted]/lib/python3.11/site-packages/django/db/backends/utils.py", line 79, in execute
    return self._execute_with_wrappers(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/[redacted]/lib/python3.11/site-packages/django/db/backends/utils.py", line 92, in _execute_with_wrappers
    return executor(sql, params, many, context)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/[redacted]/lib/python3.11/site-packages/django/db/backends/utils.py", line 100, in _execute
    with self.db.wrap_database_errors:
  File "/opt/[redacted]/lib/python3.11/site-packages/django/db/utils.py", line 91, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "/opt/[redacted]/lib/python3.11/site-packages/django/db/backends/utils.py", line 103, in _execute
    return self.cursor.execute(sql)
           ^^^^^^^^^^^^^^^^^^^^^^^^
django.db.utils.ProgrammingError: could not determine which collation to use for upper() function
HINT:  Use the COLLATE clause to set the collation explicitly.

[Aldalen]

This was tested with django 5.0.2 and latest psycopg2 2.9.9. Changing to _icontains solved the issue, but we have quite a few with _iexact....