fix(ndb): avoid unbound lock in delete callback

[lyushher]

Summary

This PR fixes a NameError that occurs when ndb.delete() is called with use_datastore=False inside a transaction while the global cache is enabled.

The transaction completion callback can reference lock even though no lock is acquired when datastore writes are disabled.

Changes

• Avoid registering the unlock callback when no lock has been acquired.
• Add a regression test covering this scenario.

Testing

python -m pytest tests/unit/test__datastore_api.py -v

All 78 tests passed.

Fixes #17926

[gemini-code-assist]

Code Review

This pull request updates the delete function in _datastore_api.py to handle cases where a global cache lock is not acquired, particularly when a transaction is active but the datastore is not used. It also adds a corresponding unit test to verify this behavior. The review feedback suggests making the lock check more explicit by using if lock is not None: instead of if lock: to prevent potential issues with falsy values.

[parthea]

Hi @lyushher,

Thanks for opening a PR! Please could you resolve the minor coverage gap?

google/cloud/ndb/_datastore_api.py              400      0    138      1    99%   465->exit

[parthea]

Thanks @lyushher!