Fix removing suggested_display_precision from entity registry

[pnbruckner]

Proposed change

When a sensor entity's suggested_display_precision is changed to None from something else, it is supposed to be removed from options of the corresponding entry in the entity registry. However, the code that is supposed to do this (SensorEntity._update_suggested_precision) has a bug that prevents it from doing so. This change fixes that bug.

Some background can be found here: pnbruckner/ha-sun2#109

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• Dependency upgrade
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Additional information

• This PR fixes or closes issue: fixes suggested_display_precision not being removed from entity registry #110668
• This PR is related to issue:
• Link to documentation pull request:

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[home-assistant]

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[gjohansson-ST]

Why is it supposed to be removed?

[pnbruckner]

Well, strictly speaking, I don't think it absolutely needs to be removed in this case, but the registry does need to be updated to be consistent with the entity's suggested_display_precision.

Currently, if the entity changes its suggested_display_precision from None to something other than None, the code will add it to the registry, and if it changes between two different non-None values, it updates the registry accordingly. However, if it changes from a non-None value to None, the bug is preventing it from updating the registry accordingly. That is what this PR fixes. I.e., it fixes the test that checks if the registry needs to be updated, not what the update does.

As far as removing as opposed to just setting it to None (i.e., null in the JSON file), since this value is optional, it does make more sense to remove it rather than simply changing it. That is how the function is currently coded. This PR does not change that aspect of the code. It just allows it to run when it should.

That is my interpretation. Maybe the original author, @emontnemery, has a different take on it.

And, FWIW, although this bug has existed since it was originally added a year ago in #87614, it probably has not been noticed because 1) most sensor entities probably don't change their suggested_display_precision from a non-None value to None, and 2) the effect of the bug is really only now apparent due to a recent frontend change (home-assistant/frontend#19396) that was released w/ 2024.2.

I noticed the bug when one of my custom sensor entities, which has a device_class of duration, changed its suggested_display_precision from 3 to None to compensate for the noted frontend change, yet the displayed value still wasn't formatted as HH:MM:SS. That's when I noticed core.entity_registry still had a suggested_display_precision of 3 for the entity instead of it being changed to null or removed.

[github-actions]

There hasn't been any activity on this pull request recently. This pull request has been automatically marked as stale because of that and will be closed if no further activity occurs within 7 days.
If you are the author of this PR, please leave a comment if you want to keep it open. Also, please rebase your PR onto the latest dev branch to ensure that it's up to date with the latest changes.
Thank you for your contribution!

[pnbruckner]

I still believe this is valid and would appreciate a review.

[emontnemery]

Thanks, @pnbruckner 👍