Allow chaining contexts (#21028)

* Allow chaining contexts

* Add stubbed out migration

homeassistant/components/automation/__init__.py

@@ -7,7 +7,7 @@ import logging
 import voluptuous as vol
 
 from homeassistant.setup import async_prepare_setup_platform
-from homeassistant.core import CoreState
+from homeassistant.core import CoreState, Context
 from homeassistant.loader import bind_hass
 from homeassistant.const import (
     ATTR_ENTITY_ID, CONF_PLATFORM, STATE_ON, SERVICE_TURN_ON, SERVICE_TURN_OFF,
@@ -280,15 +280,21 @@ class AutomationEntity(ToggleEntity, RestoreEntity):
 
         This method is a coroutine.
         """
-        if skip_condition or self._cond_func(variables):
-            self.async_set_context(context)
-            self.hass.bus.async_fire(EVENT_AUTOMATION_TRIGGERED, {
-                ATTR_NAME: self._name,
-                ATTR_ENTITY_ID: self.entity_id,
-            }, context=context)
-            await self._async_action(self.entity_id, variables, context)
-            self._last_triggered = utcnow()
-            await self.async_update_ha_state()
+        if not skip_condition and not self._cond_func(variables):
+            return
+
+        # Create a new context referring to the old context.
+        parent_id = None if context is None else context.id
+        trigger_context = Context(parent_id=parent_id)
+
+        self.async_set_context(trigger_context)
+        self.hass.bus.async_fire(EVENT_AUTOMATION_TRIGGERED, {
+            ATTR_NAME: self._name,
+            ATTR_ENTITY_ID: self.entity_id,
+        }, context=trigger_context)
+        await self._async_action(self.entity_id, variables, trigger_context)
+        self._last_triggered = utcnow()
+        await self.async_update_ha_state()
 
     async def async_will_remove_from_hass(self):
         """Remove listeners when removing automation from HASS."""