Globally available HomeAssistant object (hass)

It's now possible to get a reference to the HomeAssistant instance by calling core.async_get_hass().

Although this means it's no longer strictly necessary to pass hass around, the recommendation is still to only use core.async_get_hass where it's very cumbersome or downright impossible to pass hass to the code which needs it. An example where this can be useful is voluptuous validators, which previously couldn't access hass because voluptuous has no way of passing user data to validators.

@callback
def async_get_hass() -> HomeAssistant:
    """Return the HomeAssistant instance.
    Raises LookupError if no HomeAssistant instance is available.
    This should be used where it's very cumbersome or downright impossible to pass
    hass to the code which needs it.
    """