`validate_unit` doesn't allow valid values

[TheJulianJES]

First, validate_unit typing is Enum, although it's typed as str everywhere else, so in quirks v2 metadata, and so on.
In ZHA and HA, _attr_native_unit_of_measurement is also typed as str | None.

It should be changed to accept and return a str IMO.

The mapping is also not ideal, as we have units replicated in both zigpy and ZHA now. We should change this in the future, e.g. by just having it in zigpy (and maybe renaming the quirks/v2 where it is currently to something else). Or a separate lib?

We also need to fix not accepting the units strings that are defined, like PERCENTAGE. We need to allow those.
Actually, I don't think we really need the validation for a string anyways. Quirks v2 entities are still reviewed and obviously need to use the constants defined here before they can be merged.
HA might also already validate the units used?

Link to method (and units file):

zha/zha/units.py

Lines 179 to 181 in c013c5b

	def validate_unit(external_unit: Enum) -> Enum:
	"""Validate and return a unit of measure."""
	return UNITS_OF_MEASURE[type(external_unit).__name__](external_unit.value)

cc @prairiesnpr

[TheJulianJES]

Related (and PRs blocked by the validation):

• Sensor init fails if unit of measurement is a string #326
• Fix missing unit in _TZE200_pay2byax quirk zha-device-handlers#3563
• Add entities for Schneider Electric Thermostats zha-device-handlers#3575
• [Device Support Request] Tuya ultrasonic level sensor (TS0601 by _TZE284_kyyu8rbj) zha-device-handlers#3356
• [BUG] Why can't I use the number component fallback_name "Humidity Correction/100" when I set unit=PERCENTAGE? And I'll replace the unit with something else. zha-device-handlers#3582
• Convert Tuya gas sensors to v2, add _TZE200_hr0tdd47 zha-device-handlers#3635
• Add Tuya rain sensor _TZ3210_tgvtvdoc zha-device-handlers#3656
• Add Tuya pool sensor quirk _TZE200_v1jqz5cy zha-device-handlers#3673
• Add Nous (Tuya) SZ-T04 zha-device-handlers#3683
• TZE200_locansqn TS0601 Temp / Humi / Clock zha-device-handlers#1286

[TheJulianJES]

I'll have to double check, but I don't think ESPHome validates the provided unit_of_measurement.
HA accepts any values, even something like steps. Unit translations were also added for units like that.

In the worst case, HA logs a warning if the unit doesn't match the state class. The state class and the unit playing together is the important part. If there's no state class, all units should be valid.
Still, we review v2 quirks before merging them, so state class and units have to match. We don't have this validation for entities added in ZHA (and it's reviewed by the same people as v2 quirks).

So, we really should just drop this validation for units IMO. There's nothing positive we get from it.

[prairiesnpr]

So, we really should just drop this validation for units IMO. There's nothing positive we get from it.

Concur, I don't see a reason to validate the value in ZHA, it just adds complexity.