Make it possible to inherit EntityDescription in frozen and mutable dataclasses

[emontnemery]

Proposed change

Make it possible to inherit EntityDescription in both frozen and mutable dataclasses

Background and rationale

PR #100601 explores caching of entity properties. A major issue is that although not useful, entity descriptions are mutable, meaning we may miss changes if an integration mutates its entity descriptions.
If we make EntityDescription a frozen dataclass the problem is solved for all core integrations, but this would be a hard breaking change for custom integrations because it's a runtime error to derive a mutable dataclass from a frozen dataclass.

More details here: #100601 (comment)

Solution

Make EntityDescription behave as a dataclass, but allow it to be the base class for both frozen and mutable dataclasses. This is achieved with a metaclass FrozenOrThawed. Thanks to PEP 681 type checkers, including MyPy, keep working.

The FrozenOrThawed metaclass will look for the class argument frozen_or_thawed:

• If the flag is set on a class, the class will not be a dataclass but will behave as a dataclass.
• If the flag is not set, the metaclass does nothing and assumes the class is decorated with @dataclass.

In follow-up PRs:

• Entity descriptions of base components will also have this flag set.
• Freeze entity descriptions of all core integrations
• Log deprecation warnings if dataclasses derived from EntityDescription are not frozen

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
• I have followed the perfect PR recommendations
• The code has been formatted using Ruff (ruff format homeassistant tests)
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

If the code communicates with devices, web services, or third-party tools:

• The manifest file has all fields filled out correctly.
  Updated and included derived files by running: python3 -m script.hassfest.
• New or updated dependencies have been added to requirements_all.txt.
  Updated by running python3 -m script.gen_requirements_all.
• For the updated dependencies - a link to the changelog, or at minimum a diff between library versions is added to the PR description.
• Untested files have been added to .coveragerc.

To help with the load of incoming pull requests:

• I have reviewed two other open pull requests in this repository.

[bdraco]

This looks good

Should we do a blog post about freezing entity description dataclasses so we have a path forward to removing the compat layer?

[emontnemery]

This looks good

Should we do a blog post about freezing entity description dataclasses so we have a path forward to removing the compat layer?

Blog post added 👍

[bdraco]

Pushing the latest to my production now

[bdraco]

All good on production, nothing obvious blew up