[Samuel-Hills]

Summary

attrs currently drops slots declared directly on a slotted attrs-decorated class when it creates the replacement class. As a result, assigning to one of those declared slots raises a TypeError.

This change preserves explicitly declared slots while retaining attrs-managed fields. It also adds a regression test and changelog entry.

Fixes #1637.

Validation

• Full attrs test suite: 1406 passed, 6 skipped, 1 xfailed
• git diff --check: passed

Pull Request Checklist

• I acknowledge this project's AI policy.
• This pull request is not from my main branch.
• There's tests for all new and changed code.
• Changes or additions to public APIs are reflected in our type stubs.
  • ...and used in the stub test file typing_tests/baseline.py or, if necessary, typing_tests/mypy.py.
  • If they've been added to attr/__init__.pyi, they've also been re-imported in attrs/__init__.pyi.
• The documentation has been updated.
  • New functions/classes have to be added to docs/api.rst by hand.
  • Changes to the signatures of @attr.s() and @attrs.define() have to be added by hand too.
  • Changed/added classes/methods/functions have appropriate version directives.
  • Documentation uses semantic newlines.
• Changes have news fragments in changelog.d.