Improve error message when template is rendered from wrong thread (#117822)

* Improve error message when template is rendered from wrong thread

* Improve error message when template is rendered from wrong thread

homeassistant/helpers/template.py

@@ -688,10 +688,19 @@ class Template:
         if self.hass and self.hass.config.debug:
             self.hass.verify_event_loop_thread("async_render_to_info")
         self._renders += 1
-        assert self.hass and _render_info.get() is None
 
         render_info = RenderInfo(self)
 
+        if not self.hass:
+            raise RuntimeError(f"hass not set while rendering {self}")
+
+        if _render_info.get() is not None:
+            raise RuntimeError(
+                f"RenderInfo already set while rendering {self}, "
+                "this usually indicates the template is being rendered "
+                "in the wrong thread"
+            )
+
         if self.is_static:
             render_info._result = self.template.strip()  # noqa: SLF001
             render_info._freeze_static()  # noqa: SLF001

tests/helpers/test_template.py

@@ -119,6 +119,33 @@ def assert_result_info(
         assert not hasattr(info, "_domains")
 
 
+async def test_template_render_missing_hass(hass: HomeAssistant) -> None:
+    """Test template render when hass is not set."""
+    hass.states.async_set("sensor.test", "23")
+    template_str = "{{ states('sensor.test') }}"
+    template_obj = template.Template(template_str, None)
+    template._render_info.set(template.RenderInfo(template_obj))
+
+    with pytest.raises(RuntimeError, match="hass not set while rendering"):
+        template_obj.async_render_to_info()
+
+
+async def test_template_render_info_collision(hass: HomeAssistant) -> None:
+    """Test template render info collision.
+
+    This usually means the template is being rendered
+    in the wrong thread.
+    """
+    hass.states.async_set("sensor.test", "23")
+    template_str = "{{ states('sensor.test') }}"
+    template_obj = template.Template(template_str, None)
+    template_obj.hass = hass
+    template._render_info.set(template.RenderInfo(template_obj))
+
+    with pytest.raises(RuntimeError, match="RenderInfo already set while rendering"):
+        template_obj.async_render_to_info()
+
+
 def test_template_equality() -> None:
     """Test template comparison and hashing."""
     template_one = template.Template("{{ template_one }}")