SNOW-2149491: Alembic autogenerate workflow breaks with get_multi_indexes()

[jasonkoverantos]

We have observed a regression in our alembic migration workflow recently. Now, when we try to autogenerate an alembic revision, we are getting the error:

INFO  [alembic.runtime.migration] Context impl SnowflakeImpl.
INFO  [alembic.runtime.migration] Will assume non-transactional DDL.
Traceback (most recent call last):
  File "/Users/jko/Core-Product/verantos-evidence-platform/libs/backend/core/migrations/.venv/bin/alembic", line 8, in <module>
    sys.exit(main())
             ^^^^^^
  File "/Users/jko/Core-Product/verantos-evidence-platform/libs/backend/core/migrations/.venv/lib/python3.12/site-packages/alembic/config.py", line 988, in main
    CommandLine(prog=prog).main(argv=argv)
  File "/Users/jko/Core-Product/verantos-evidence-platform/libs/backend/core/migrations/.venv/lib/python3.12/site-packages/alembic/config.py", line 978, in main
    self.run_cmd(cfg, options)
  File "/Users/jko/Core-Product/verantos-evidence-platform/libs/backend/core/migrations/.venv/lib/python3.12/site-packages/alembic/config.py", line 912, in run_cmd
    fn(
  File "/Users/jko/Core-Product/verantos-evidence-platform/libs/backend/core/migrations/.venv/lib/python3.12/site-packages/alembic/command.py", line 309, in revision
    script_directory.run_env()
  File "/Users/jko/Core-Product/verantos-evidence-platform/libs/backend/core/migrations/.venv/lib/python3.12/site-packages/alembic/script/base.py", line 551, in run_env
    util.load_python_file(self.dir, "env.py")
  File "/Users/jko/Core-Product/verantos-evidence-platform/libs/backend/core/migrations/.venv/lib/python3.12/site-packages/alembic/util/pyfiles.py", line 114, in load_python_file
    module = load_module_py(module_id, path)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/jko/Core-Product/verantos-evidence-platform/libs/backend/core/migrations/.venv/lib/python3.12/site-packages/alembic/util/pyfiles.py", line 134, in load_module_py
    spec.loader.exec_module(module)  # type: ignore
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<frozen importlib._bootstrap_external>", line 999, in exec_module
  File "<frozen importlib._bootstrap>", line 488, in _call_with_frames_removed
  File "/Users/jko/Core-Product/verantos-evidence-platform/libs/backend/core/migrations/migrations/alembic/env.py", line 160, in <module>
    run_migrations_online()
  File "/Users/jko/Core-Product/verantos-evidence-platform/libs/backend/core/migrations/migrations/alembic/env.py", line 154, in run_migrations_online
    context.run_migrations()
  File "<string>", line 8, in run_migrations
  File "/Users/jko/Core-Product/verantos-evidence-platform/libs/backend/core/migrations/.venv/lib/python3.12/site-packages/alembic/runtime/environment.py", line 946, in run_migrations
    self.get_context().run_migrations(**kw)
  File "/Users/jko/Core-Product/verantos-evidence-platform/libs/backend/core/migrations/.venv/lib/python3.12/site-packages/alembic/runtime/migration.py", line 611, in run_migrations
    for step in self._migrations_fn(heads, self):
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/jko/Core-Product/verantos-evidence-platform/libs/backend/core/migrations/.venv/lib/python3.12/site-packages/alembic/command.py", line 285, in retrieve_migrations
    revision_context.run_autogenerate(rev, context)
  File "/Users/jko/Core-Product/verantos-evidence-platform/libs/backend/core/migrations/.venv/lib/python3.12/site-packages/alembic/autogenerate/api.py", line 570, in run_autogenerate
    self._run_environment(rev, migration_context, True)
  File "/Users/jko/Core-Product/verantos-evidence-platform/libs/backend/core/migrations/.venv/lib/python3.12/site-packages/alembic/autogenerate/api.py", line 617, in _run_environment
    compare._populate_migration_script(
  File "/Users/jko/Core-Product/verantos-evidence-platform/libs/backend/core/migrations/.venv/lib/python3.12/site-packages/alembic/autogenerate/compare.py", line 66, in _populate_migration_script
    _produce_net_changes(autogen_context, upgrade_ops)
  File "/Users/jko/Core-Product/verantos-evidence-platform/libs/backend/core/migrations/.venv/lib/python3.12/site-packages/alembic/autogenerate/compare.py", line 99, in _produce_net_changes
    comparators.dispatch("schema", autogen_context.dialect.name)(
  File "/Users/jko/Core-Product/verantos-evidence-platform/libs/backend/core/migrations/.venv/lib/python3.12/site-packages/alembic/util/langhelpers.py", line 310, in go
    fn(*arg, **kw)
  File "/Users/jko/Core-Product/verantos-evidence-platform/libs/backend/core/migrations/.venv/lib/python3.12/site-packages/alembic/autogenerate/compare.py", line 138, in _autogen_for_tables
    _compare_tables(
  File "/Users/jko/Core-Product/verantos-evidence-platform/libs/backend/core/migrations/.venv/lib/python3.12/site-packages/alembic/autogenerate/compare.py", line 250, in _compare_tables
    _InspectorConv(inspector).reflect_table(t, include_columns=None)
  File "/Users/jko/Core-Product/verantos-evidence-platform/libs/backend/core/migrations/.venv/lib/python3.12/site-packages/alembic/autogenerate/compare.py", line 483, in reflect_table
    self.inspector.reflect_table(table, include_columns=include_columns)
  File "/Users/jko/Core-Product/verantos-evidence-platform/libs/backend/core/migrations/.venv/lib/python3.12/site-packages/sqlalchemy/engine/reflection.py", line 1536, in reflect_table
    _reflect_info = self._get_reflection_info(
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/jko/Core-Product/verantos-evidence-platform/libs/backend/core/migrations/.venv/lib/python3.12/site-packages/sqlalchemy/engine/reflection.py", line 2024, in _get_reflection_info
    indexes=run(self.get_multi_indexes),
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/jko/Core-Product/verantos-evidence-platform/libs/backend/core/migrations/.venv/lib/python3.12/site-packages/sqlalchemy/engine/reflection.py", line 2005, in run
    res = meth(filter_names=_fn, **kw)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/jko/Core-Product/verantos-evidence-platform/libs/backend/core/migrations/.venv/lib/python3.12/site-packages/sqlalchemy/engine/reflection.py", line 1195, in get_multi_indexes
    self.dialect.get_multi_indexes(
  File "/Users/jko/Core-Product/verantos-evidence-platform/libs/backend/core/migrations/.venv/lib/python3.12/site-packages/snowflake/sqlalchemy/snowdialect.py", line 958, in get_multi_indexes
    indexes[(schema, table_name)] = indexes[(schema, table_name)].append(
                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'append'

Has anything changed with the get_multi_indexes() functionality recently?

[sfc-gh-vpardeshi]

File: snowflake/sqlalchemy/snowdialect.py
Line Number: 958
Issue Line: indexes[(schema, table_name)] = indexes[(schema, table_name)].append(index)
Issue: The above line of code generates a "None" value and assigns it to the tuple in the indexes dictionary
Resolution: indexes[(schema, table_name)].append(index)

Hi Team,
Would appreciate it if you could help analyze and resolve the issue.
Thanks