Register trigger platform upon use (#166911)

homeassistant/helpers/trigger.py

@@ -202,22 +202,28 @@ async def _register_trigger_platform(
     from homeassistant.components import automation  # noqa: PLC0415
 
     new_triggers: set[str] = set()
+    triggers = hass.data[TRIGGERS]
 
     if hasattr(platform, "async_get_triggers"):
-        for trigger_key in await platform.async_get_triggers(hass):
+        all_triggers = await platform.async_get_triggers(hass)
+        for trigger_key in all_triggers:
             trigger_key = get_absolute_description_key(integration_domain, trigger_key)
-            hass.data[TRIGGERS][trigger_key] = integration_domain
-            new_triggers.add(trigger_key)
+            if trigger_key not in triggers:
+                triggers[trigger_key] = integration_domain
+                new_triggers.add(trigger_key)
         if not new_triggers:
-            _LOGGER.debug(
-                "Integration %s returned no triggers in async_get_triggers",
-                integration_domain,
-            )
+            if not all_triggers:
+                _LOGGER.debug(
+                    "Integration %s returned no triggers in async_get_triggers",
+                    integration_domain,
+                )
             return
     elif hasattr(platform, "async_validate_trigger_config") or hasattr(
         platform, "TRIGGER_SCHEMA"
     ):
-        hass.data[TRIGGERS][integration_domain] = integration_domain
+        if integration_domain in triggers:
+            return
+        triggers[integration_domain] = integration_domain
         new_triggers.add(integration_domain)
     else:
         _LOGGER.debug(
@@ -1184,12 +1190,17 @@ async def _async_get_trigger_platform(
     except IntegrationNotFound:
         raise vol.Invalid(f"Invalid trigger '{trigger_key}' specified") from None
     try:
-        return platform, await integration.async_get_platform("trigger")
+        platform_module = await integration.async_get_platform("trigger")
     except ImportError:
         raise vol.Invalid(
             f"Integration '{platform}' does not provide trigger support"
         ) from None
 
+    # Ensure triggers are registered so descriptions can be loaded
+    await _register_trigger_platform(hass, platform, platform_module)
+
+    return platform, platform_module
+
 
 async def async_validate_trigger_config(
     hass: HomeAssistant, trigger_config: list[ConfigType]

tests/helpers/test_trigger.py

@@ -42,6 +42,7 @@ from homeassistant.helpers.automation import (
 )
 from homeassistant.helpers.trigger import (
     DATA_PLUGGABLE_ACTIONS,
+    TRIGGERS,
     EntityNumericalStateChangedTriggerWithUnitBase,
     EntityNumericalStateCrossedThresholdTriggerWithUnitBase,
     EntityTriggerBase,
@@ -669,6 +670,51 @@ async def test_platform_backwards_compatibility_for_new_style_configs(
     assert result == config_old_style
 
 
+async def test_get_trigger_platform_registers_triggers(
+    hass: HomeAssistant,
+) -> None:
+    """Test _async_get_trigger_platform registers triggers and notifies subscribers."""
+
+    class MockTrigger(Trigger):
+        """Mock trigger."""
+
+        async def async_attach_runner(
+            self, run_action: TriggerActionRunner
+        ) -> CALLBACK_TYPE:
+            return lambda: None
+
+    async def async_get_triggers(
+        hass: HomeAssistant,
+    ) -> dict[str, type[Trigger]]:
+        return {"trig_a": MockTrigger, "trig_b": MockTrigger}
+
+    mock_integration(hass, MockModule("test"))
+    mock_platform(hass, "test.trigger", Mock(async_get_triggers=async_get_triggers))
+
+    subscriber_events: list[set[str]] = []
+
+    async def subscriber(new_triggers: set[str]) -> None:
+        subscriber_events.append(new_triggers)
+
+    trigger.async_subscribe_platform_events(hass, subscriber)
+
+    assert "test.trig_a" not in hass.data[TRIGGERS]
+    assert "test.trig_b" not in hass.data[TRIGGERS]
+
+    # First call registers all triggers from the platform and notifies subscribers
+    await _async_get_trigger_platform(hass, "test.trig_a")
+
+    assert hass.data[TRIGGERS]["test.trig_a"] == "test"
+    assert hass.data[TRIGGERS]["test.trig_b"] == "test"
+    assert len(subscriber_events) == 1
+    assert subscriber_events[0] == {"test.trig_a", "test.trig_b"}
+
+    # Subsequent calls are idempotent — no re-registration or re-notification
+    await _async_get_trigger_platform(hass, "test.trig_a")
+    await _async_get_trigger_platform(hass, "test.trig_b")
+    assert len(subscriber_events) == 1
+
+
 @pytest.mark.parametrize(
     "sun_trigger_descriptions",
     [