Ensure template tracking can recover after the template generates an exception (#39256)

homeassistant/helpers/event.py

@@ -562,6 +562,11 @@ class _TrackTemplateResultInfo:
         entities = set(self._info.entities)
         for entity_id in self.hass.states.async_entity_ids(self._info.domains):
             entities.add(entity_id)
+
+        # Entities has changed to none
+        if not entities:
+            return
+
         self._entities_listener = async_track_state_change_event(
             self.hass, entities, self._refresh
         )
@@ -570,6 +575,10 @@ class _TrackTemplateResultInfo:
     def _setup_domains_listener(self) -> None:
         assert self._info
 
+        # Domains has changed to none
+        if not self._info.domains:
+            return
+
         self._domains_listener = async_track_state_added_domain(
             self.hass, self._info.domains, self._refresh
         )

tests/helpers/test_event.py

@@ -543,6 +543,33 @@ async def test_track_template_error(hass, caplog):
     assert "TemplateAssertionError" not in caplog.text
 
 
+async def test_track_template_error_can_recover(hass, caplog):
+    """Test tracking template with error."""
+    hass.states.async_set("switch.data_system", "cow", {"opmode": 0})
+    template_error = Template(
+        "{{ states.sensor.data_system.attributes['opmode'] == '0' }}", hass
+    )
+    error_calls = []
+
+    @ha.callback
+    def error_callback(entity_id, old_state, new_state):
+        error_calls.append((entity_id, old_state, new_state))
+
+    async_track_template(hass, template_error, error_callback)
+    await hass.async_block_till_done()
+    assert not error_calls
+
+    hass.states.async_remove("switch.data_system")
+
+    assert "UndefinedError" in caplog.text
+
+    hass.states.async_set("switch.data_system", "cow", {"opmode": 0})
+
+    caplog.clear()
+
+    assert "UndefinedError" not in caplog.text
+
+
 async def test_track_template_result(hass):
     """Test tracking template."""
     specific_runs = []