Warn if unit_of_measurement is set on instances of SensorEntityDescription (#54867)

* Add class BaseEntityDescription without unit_of_measurement

* Refactor according to review comments

* Tweak

* Fix offending integrations

* Fix offending integrations

homeassistant/components/sensor/__init__.py

@@ -5,6 +5,7 @@ from collections.abc import Mapping
 from contextlib import suppress
 from dataclasses import dataclass
 from datetime import datetime, timedelta
+import inspect
 import logging
 from typing import Any, Final, cast, final
 
@@ -128,9 +129,31 @@ async def async_unload_entry(hass: HomeAssistant, entry: ConfigEntry) -> bool:
 class SensorEntityDescription(EntityDescription):
     """A class that describes sensor entities."""
 
-    state_class: str | None = None
     last_reset: datetime | None = None  # Deprecated, to be removed in 2021.11
     native_unit_of_measurement: str | None = None
+    state_class: str | None = None
+    unit_of_measurement: None = None  # Type override, use native_unit_of_measurement
+
+    def __post_init__(self) -> None:
+        """Post initialisation processing."""
+        if self.unit_of_measurement:
+            caller = inspect.stack()[2]  # type: ignore[unreachable]
+            module = inspect.getmodule(caller[0])
+            if "custom_components" in module.__file__:
+                report_issue = "report it to the custom component author."
+            else:
+                report_issue = (
+                    "create a bug report at "
+                    "https://github.com/home-assistant/core/issues?q=is%3Aopen+is%3Aissue"
+                )
+            _LOGGER.warning(
+                "%s is setting 'unit_of_measurement' on an instance of "
+                "SensorEntityDescription, this is not valid and will be unsupported "
+                "from Home Assistant 2021.11. Please %s",
+                module.__name__,
+                report_issue,
+            )
+            self.native_unit_of_measurement = self.unit_of_measurement
 
 
 class SensorEntity(Entity):
@@ -220,11 +243,6 @@ class SensorEntity(Entity):
             and self._attr_unit_of_measurement is not None
         ):
             return self._attr_unit_of_measurement
-        if (
-            hasattr(self, "entity_description")
-            and self.entity_description.unit_of_measurement is not None
-        ):
-            return self.entity_description.unit_of_measurement
 
         native_unit_of_measurement = self.native_unit_of_measurement