Sub-second duration on entities card

[jhansche]

This came out of an issue with how the new sensor entities work in the ping integration, and how it "feels" wrong compared to the old way of getting the same value as a Template sensor: home-assistant/core#118183 (comment)

The short version is that the Template approach would render as Router Ping ... 12.345 ms (with units and sub-ms precision) in the entities card; while the new sensor renders as Router ping ... 0.012 (no units, and the value is truncated at 1/1000 sec, or rounded to the nearest millisecond). Example from the link above:

The reason is because the new Ping integration's sensor type declares device_class: duration, which is accurate. But the frontend renders a duration here with the assumption that it will be formatted as "HH:mm:ss.SSS". For a Duration that is less than one second, that results in ss.SSS format, which is why the above screenshot only shows 0.001.

Instead, I think it would make more sense to render these values with rules similar to what we see in format_duration.

[karwosts]

If you set a display_precision on your entity, I believe it will not use HH:mm:ss format and instead render with the exact unit_of_measurement and requested number of decimal points.

[jhansche]

Related: is this something that the integration can choose to set in its SensorEntityDescription to work this way by default? 🤔

[karwosts]

I'm not sure, to be honest this is a bit of a hack/compromise on how to show duration sensors, it wasn't initially planned this way but display_precision wasn't otherwise used for duration sensors, so this was just added as a way to bypass the default display.

Could probably benefit from some additional design on how to handle durations at various extremes, like multiple days or sub seconds.

[jhansche]

Looks like there is a suggested_display_precision. I'll propose that as an alternative for this scenario, given the ping integration's round-trip time will virtually never exceed the order of "seconds".

[karwosts]

Looking at frontend code I think that might not work, I think it has to be the user selected precision.

If you (or the ping integration author) wants to try that route, and you find it's not working, open a frontend issue and I'll try to look further.

[karwosts]

Hmm yeah history stats already seems to set suggested_display_precision = 2, for a duration sensor, and that still shows as hh:mm:ss.