Use display_precision if suggested_display_precision is None

[rikroe]

Proposed change

This PR fixes unit conversion behavior for sensors if display_precision is set (by the user) but suggested_display_precision (set by the integration) is None.

Before, a suggested_display_precision of None would always cause the converted value to be rounded to 0 decimal places.

A suggested_display_precision of 0 does not show this behaviour.

Example

native_value: 6
native_unit_of_measurement: L
display_precision: 2 (set in the entity settings via UI)

Converted to gallons:
value: 2.0 - but should be 1.59
native_unit_of_measurement: gal

Cause

This happens due to https://github.com/home-assistant/core/blob/dev/homeassistant/components/sensor/__init__.py#L702-L724 which falls back to deducing the required precision if no suggested precision or sensor option for display precision is set.

_sensor_option_display_precision itself is set by _suggested_precision_or_none() which until now only read the suggested precision and not what the user had stored.

The added test case would fail without the changes to components/sensor/__init__.py as entity's state would be 621.0.

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:

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[home-assistant]

Hey there @home-assistant/core, mind taking a look at this pull request as it has been labeled with an integration (sensor) you are listed as a code owner for? Thanks!

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[lellky]

Looks good to me!

[emontnemery]

Thanks a lot @rikroe 👍

[rikroe]

Thanks for looking into it! I can look into that only later tonight if needed.

[bdraco]

Thanks @rikroe @emontnemery