From f8755a52c2c2a548f8e6c48f94b3662082fa4213 Mon Sep 17 00:00:00 2001
From: Erik Montnemery <erik@montnemery.com>
Date: Sat, 20 Mar 2021 15:16:04 +0100
Subject: [PATCH] Warn on undefined variables in templates (#48140)

* Warn on undefined variables in templates

* Add test

* fix tests

* fix tests
---
 homeassistant/helpers/template.py        |  2 +-
 tests/components/influxdb/test_sensor.py | 16 +++++++++++++---
 tests/helpers/test_script.py             |  3 +--
 tests/helpers/test_template.py           |  7 +++++++
 4 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/homeassistant/helpers/template.py b/homeassistant/helpers/template.py
index cfb7223752e..24c91ec5468 100644
--- a/homeassistant/helpers/template.py
+++ b/homeassistant/helpers/template.py
@@ -1318,7 +1318,7 @@ class TemplateEnvironment(ImmutableSandboxedEnvironment):
 
     def __init__(self, hass, limited=False):
         """Initialise template environment."""
-        super().__init__()
+        super().__init__(undefined=jinja2.make_logging_undefined(logger=_LOGGER))
         self.hass = hass
         self.template_cache = weakref.WeakValueDictionary()
         self.filters["round"] = forgiving_round
diff --git a/tests/components/influxdb/test_sensor.py b/tests/components/influxdb/test_sensor.py
index 55172011f4f..9a353f59e42 100644
--- a/tests/components/influxdb/test_sensor.py
+++ b/tests/components/influxdb/test_sensor.py
@@ -442,7 +442,7 @@ async def test_error_querying_influx(
 
 
 @pytest.mark.parametrize(
-    "mock_client, config_ext, queries, set_query_mock, make_resultset",
+    "mock_client, config_ext, queries, set_query_mock, make_resultset, key",
     [
         (
             DEFAULT_API_VERSION,
@@ -459,6 +459,7 @@ async def test_error_querying_influx(
             },
             _set_query_mock_v1,
             _make_v1_resultset,
+            "where",
         ),
         (
             API_VERSION_2,
@@ -466,12 +467,13 @@ async def test_error_querying_influx(
             {"queries_flux": [{"name": "test", "query": "{{ illegal.template }}"}]},
             _set_query_mock_v2,
             _make_v2_resultset,
+            "query",
         ),
     ],
     indirect=["mock_client"],
 )
 async def test_error_rendering_template(
-    hass, caplog, mock_client, config_ext, queries, set_query_mock, make_resultset
+    hass, caplog, mock_client, config_ext, queries, set_query_mock, make_resultset, key
 ):
     """Test behavior of sensor with error rendering template."""
     set_query_mock(mock_client, return_value=make_resultset(42))
@@ -479,7 +481,15 @@ async def test_error_rendering_template(
     sensors = await _setup(hass, config_ext, queries, ["sensor.test"])
     assert sensors[0].state == STATE_UNKNOWN
     assert (
-        len([record for record in caplog.records if record.levelname == "ERROR"]) == 1
+        len(
+            [
+                record
+                for record in caplog.records
+                if record.levelname == "ERROR"
+                and f"Could not render {key} template" in record.msg
+            ]
+        )
+        == 1
     )
 
 
diff --git a/tests/helpers/test_script.py b/tests/helpers/test_script.py
index 1f47aa9dbba..8a93d769775 100644
--- a/tests/helpers/test_script.py
+++ b/tests/helpers/test_script.py
@@ -1277,8 +1277,7 @@ async def test_repeat_condition_warning(hass, caplog, condition):
     hass.async_create_task(script_obj.async_run(context=Context()))
     await asyncio.wait_for(hass.async_block_till_done(), 1)
 
-    assert len(caplog.record_tuples) == 1
-    assert caplog.record_tuples[0][1] == logging.WARNING
+    assert f"Error in '{condition}[0]' evaluation" in caplog.text
 
     assert len(events) == count
 
diff --git a/tests/helpers/test_template.py b/tests/helpers/test_template.py
index 193c7e2aa55..da6a8663cc3 100644
--- a/tests/helpers/test_template.py
+++ b/tests/helpers/test_template.py
@@ -2497,3 +2497,10 @@ async def test_parse_result(hass):
         ("0011101.00100001010001", "0011101.00100001010001"),
     ):
         assert template.Template(tpl, hass).async_render() == result
+
+
+async def test_undefined_variable(hass, caplog):
+    """Test a warning is logged on undefined variables."""
+    tpl = template.Template("{{ no_such_variable }}", hass)
+    assert tpl.async_render() == ""
+    assert "Template variable warning: no_such_variable is undefined" in caplog.text