Send template render errors to template helper preview (#99716)

homeassistant/components/template/template_entity.py

@@ -15,13 +15,11 @@
     CONF_ICON,
     CONF_ICON_TEMPLATE,
     CONF_NAME,
-    EVENT_HOMEASSISTANT_START,
     STATE_UNKNOWN,
 )
 from homeassistant.core import (
     CALLBACK_TYPE,
     Context,
-    CoreState,
     HomeAssistant,
     State,
     callback,
@@ -38,6 +36,7 @@
     async_track_template_result,
 )
 from homeassistant.helpers.script import Script, _VarsType
+from homeassistant.helpers.start import async_at_start
 from homeassistant.helpers.template import (
     Template,
     TemplateStateFromEntityId,
@@ -442,7 +441,11 @@ def _handle_results(
             )
 
     @callback
-    def _async_template_startup(self, *_: Any) -> None:
+    def _async_template_startup(
+        self,
+        _hass: HomeAssistant | None,
+        log_fn: Callable[[int, str], None] | None = None,
+    ) -> None:
         template_var_tups: list[TrackTemplate] = []
         has_availability_template = False
 
@@ -467,6 +470,7 @@ def _async_template_startup(self, *_: Any) -> None:
             self.hass,
             template_var_tups,
             self._handle_results,
+            log_fn=log_fn,
             has_super_template=has_availability_template,
         )
         self.async_on_remove(result_info.async_remove)
@@ -515,10 +519,13 @@ def async_start_preview(
     ) -> CALLBACK_TYPE:
         """Render a preview."""
 
+        def log_template_error(level: int, msg: str) -> None:
+            preview_callback(None, None, None, msg)
+
         self._preview_callback = preview_callback
         self._async_setup_templates()
         try:
-            self._async_template_startup()
+            self._async_template_startup(None, log_template_error)
         except Exception as err:  # pylint: disable=broad-exception-caught
             preview_callback(None, None, None, str(err))
         return self._call_on_remove_callbacks
@@ -527,13 +534,7 @@ async def async_added_to_hass(self) -> None:
         """Run when entity about to be added to hass."""
         self._async_setup_templates()
 
-        if self.hass.state == CoreState.running:
-            self._async_template_startup()
-            return
-
-        self.hass.bus.async_listen_once(
-            EVENT_HOMEASSISTANT_START, self._async_template_startup
-        )
+        async_at_start(self.hass, self._async_template_startup)
 
     async def async_update(self) -> None:
         """Call for forced update."""

homeassistant/helpers/event.py

@@ -957,11 +957,14 @@ def async_setup(
             if info.exception:
                 if raise_on_template_error:
                     raise info.exception
-                _LOGGER.error(
-                    "Error while processing template: %s",
-                    track_template_.template,
-                    exc_info=info.exception,
-                )
+                if not log_fn:
+                    _LOGGER.error(
+                        "Error while processing template: %s",
+                        track_template_.template,
+                        exc_info=info.exception,
+                    )
+                else:
+                    log_fn(logging.ERROR, str(info.exception))
 
         self._track_state_changes = async_track_state_change_filtered(
             self.hass, _render_infos_to_track_states(self._info.values()), self._refresh

tests/components/template/test_config_flow.py

@@ -272,12 +272,12 @@ async def test_options(
         ),
         (
             "sensor",
-            "{{ float(states('sensor.one')) + float(states('sensor.two')) }}",
+            "{{ float(states('sensor.one'), default='') + float(states('sensor.two'), default='') }}",
             {},
             {"one": "30.0", "two": "20.0"},
-            ["unavailable", "50.0"],
+            ["", "50.0"],
             [{}, {}],
-            [["one"], ["one", "two"]],
+            [["one", "two"], ["one", "two"]],
         ),
     ),
 )
@@ -470,6 +470,173 @@ async def test_config_flow_preview_bad_input(
     }
 
 
+@pytest.mark.parametrize(
+    (
+        "template_type",
+        "state_template",
+        "input_states",
+        "template_states",
+        "error_events",
+    ),
+    [
+        (
+            "sensor",
+            "{{ float(states('sensor.one')) + float(states('sensor.two')) }}",
+            {"one": "30.0", "two": "20.0"},
+            ["unavailable", "50.0"],
+            [
+                (
+                    "ValueError: Template error: float got invalid input 'unknown' "
+                    "when rendering template '{{ float(states('sensor.one')) + "
+                    "float(states('sensor.two')) }}' but no default was specified"
+                )
+            ],
+        ),
+    ],
+)
+async def test_config_flow_preview_template_startup_error(
+    hass: HomeAssistant,
+    hass_ws_client: WebSocketGenerator,
+    template_type: str,
+    state_template: str,
+    input_states: dict[str, str],
+    template_states: list[str],
+    error_events: list[str],
+) -> None:
+    """Test the config flow preview."""
+    client = await hass_ws_client(hass)
+
+    input_entities = ["one", "two"]
+
+    result = await hass.config_entries.flow.async_init(
+        DOMAIN, context={"source": config_entries.SOURCE_USER}
+    )
+    assert result["type"] == FlowResultType.MENU
+
+    result = await hass.config_entries.flow.async_configure(
+        result["flow_id"],
+        {"next_step_id": template_type},
+    )
+    await hass.async_block_till_done()
+    assert result["type"] == FlowResultType.FORM
+    assert result["step_id"] == template_type
+    assert result["errors"] is None
+    assert result["preview"] == "template"
+
+    await client.send_json_auto_id(
+        {
+            "type": "template/start_preview",
+            "flow_id": result["flow_id"],
+            "flow_type": "config_flow",
+            "user_input": {"name": "My template", "state": state_template},
+        }
+    )
+    msg = await client.receive_json()
+    assert msg["type"] == "result"
+    assert msg["success"]
+
+    for error_event in error_events:
+        msg = await client.receive_json()
+        assert msg["type"] == "event"
+        assert msg["event"] == {"error": error_event}
+
+    msg = await client.receive_json()
+    assert msg["type"] == "event"
+    assert msg["event"]["state"] == template_states[0]
+
+    for input_entity in input_entities:
+        hass.states.async_set(
+            f"{template_type}.{input_entity}", input_states[input_entity], {}
+        )
+
+    msg = await client.receive_json()
+    assert msg["type"] == "event"
+    assert msg["event"]["state"] == template_states[1]
+
+
+@pytest.mark.parametrize(
+    (
+        "template_type",
+        "state_template",
+        "input_states",
+        "template_states",
+        "error_events",
+    ),
+    [
+        (
+            "sensor",
+            "{{ float(states('sensor.one')) > 30 and undefined_function() }}",
+            [{"one": "30.0", "two": "20.0"}, {"one": "35.0", "two": "20.0"}],
+            ["False", "unavailable"],
+            ["'undefined_function' is undefined"],
+        ),
+    ],
+)
+async def test_config_flow_preview_template_error(
+    hass: HomeAssistant,
+    hass_ws_client: WebSocketGenerator,
+    template_type: str,
+    state_template: str,
+    input_states: list[dict[str, str]],
+    template_states: list[str],
+    error_events: list[str],
+) -> None:
+    """Test the config flow preview."""
+    client = await hass_ws_client(hass)
+
+    input_entities = ["one", "two"]
+
+    for input_entity in input_entities:
+        hass.states.async_set(
+            f"{template_type}.{input_entity}", input_states[0][input_entity], {}
+        )
+
+    result = await hass.config_entries.flow.async_init(
+        DOMAIN, context={"source": config_entries.SOURCE_USER}
+    )
+    assert result["type"] == FlowResultType.MENU
+
+    result = await hass.config_entries.flow.async_configure(
+        result["flow_id"],
+        {"next_step_id": template_type},
+    )
+    await hass.async_block_till_done()
+    assert result["type"] == FlowResultType.FORM
+    assert result["step_id"] == template_type
+    assert result["errors"] is None
+    assert result["preview"] == "template"
+
+    await client.send_json_auto_id(
+        {
+            "type": "template/start_preview",
+            "flow_id": result["flow_id"],
+            "flow_type": "config_flow",
+            "user_input": {"name": "My template", "state": state_template},
+        }
+    )
+    msg = await client.receive_json()
+    assert msg["type"] == "result"
+    assert msg["success"]
+
+    msg = await client.receive_json()
+    assert msg["type"] == "event"
+    assert msg["event"]["state"] == template_states[0]
+
+    for input_entity in input_entities:
+        hass.states.async_set(
+            f"{template_type}.{input_entity}", input_states[1][input_entity], {}
+        )
+
+    for error_event in error_events:
+        msg = await client.receive_json()
+        assert msg["type"] == "event"
+        assert msg["event"] == {"error": error_event}
+
+    msg = await client.receive_json()
+    assert msg["type"] == "event"
+    assert msg["event"]["state"] == template_states[1]
+
+
 @pytest.mark.parametrize(
     (
         "template_type",