[api] Treat homeassistant.event variables as lambdas (#18759)

tests/component_tests/api/test_homeassistant_variables.py

@@ -0,0 +1,63 @@
+"""Tests for variables handling in homeassistant.event and homeassistant.action."""
+
+from collections.abc import Callable
+import logging
+from pathlib import Path
+
+import pytest
+
+CONFIG = "tests/component_tests/api/test_homeassistant_variables.yaml"
+
+
+def test_plain_string_with_return_is_compiled_as_lambda_with_warning(
+    generate_main: Callable[[str | Path], str],
+    caplog: pytest.LogCaptureFixture,
+) -> None:
+    """A plain string with a return statement compiles as a lambda and warns."""
+    with caplog.at_level(logging.WARNING):
+        main_cpp = generate_main(CONFIG)
+
+    assert main_cpp.count('add_variable(ESPHOME_F("lambda_var"), []() {') == 2
+    assert "return millis();" in main_cpp
+    # The source text must not be sent as a static string value.
+    assert '"return millis();"' not in main_cpp
+    assert "missing the !lambda tag" in caplog.text
+
+
+def test_static_string_is_kept_as_static_value(
+    generate_main: Callable[[str | Path], str],
+    caplog: pytest.LogCaptureFixture,
+) -> None:
+    """A static string stays static, PROGMEM wrapped, with no warning."""
+    with caplog.at_level(logging.WARNING):
+        main_cpp = generate_main(CONFIG)
+
+    assert (
+        main_cpp.count(
+            'add_variable(ESPHOME_F("static_var"), ESPHOME_F("static value"));'
+        )
+        == 2
+    )
+    assert "static value" not in caplog.text
+
+
+def test_static_id_value_stays_literal_with_hint(
+    generate_main: Callable[[str | Path], str],
+    caplog: pytest.LogCaptureFixture,
+) -> None:
+    """Lambda source without a return stays literal text but warns."""
+    with caplog.at_level(logging.WARNING):
+        main_cpp = generate_main(CONFIG)
+
+    assert 'ESPHOME_F("id(test_sensor).state")' in main_cpp
+    assert "sent as literal text" in caplog.text
+
+
+def test_explicit_lambda_tag_is_compiled_as_lambda(
+    generate_main: Callable[[str | Path], str],
+) -> None:
+    """A !lambda value keeps working unchanged."""
+    main_cpp = generate_main(CONFIG)
+
+    assert 'add_variable(ESPHOME_F("tagged_var"), []() {' in main_cpp
+    assert "return App.get_name();" in main_cpp

tests/component_tests/api/test_homeassistant_variables.yaml

@@ -0,0 +1,32 @@
+esphome:
+  name: test
+  on_boot:
+    then:
+      # Plain strings with a return statement compile as lambdas
+      - homeassistant.event:
+          event: esphome.test_event
+          data_template:
+            message: "{{ lambda_var }} {{ static_var }} {{ tagged_var }}"
+          variables:
+            lambda_var: |-
+              return millis();
+            static_var: static value
+            tagged_var: !lambda return App.get_name();
+            hint_var: id(test_sensor).state
+      - homeassistant.action:
+          action: notify.notify
+          data_template:
+            message: "{{ lambda_var }} {{ static_var }}"
+          variables:
+            lambda_var: |-
+              return millis();
+            static_var: static value
+
+esp32:
+  board: esp32dev
+
+wifi:
+  ssid: SomeNetwork
+  password: SomePassword
+
+api: