[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:

tests/components/api/common-base.yaml

@@ -9,6 +9,14 @@ esphome:
           event: esphome.button_pressed
           data:
             message: Button was pressed
+      - homeassistant.event:
+          event: esphome.button_pressed_with_variables
+          data_template:
+            message: Button {{ button_name }} ({{ button_index }}) was pressed from {{ button_source }}
+          variables:
+            button_name: !lambda 'return std::string("test_button");'
+            button_index: !lambda 'return 1;'
+            button_source: static_value
       - homeassistant.action:
           action: notify.html5
           data:

tests/components/homeassistant/common.yaml

@@ -12,7 +12,7 @@ esphome:
           data_template:
             message: The humidity is {{ my_variable }}%.
           variables:
-            my_variable: "return id(ha_hello_world_temperature).state;"
+            my_variable: !lambda "return id(ha_hello_world_temperature).state;"
       - homeassistant.action:
           action: notify.html5
           data:
@@ -24,7 +24,7 @@ esphome:
           data_template:
             message: The humidity is {{ my_variable }}%.
           variables:
-            my_variable: "return id(ha_hello_world_temperature).state;"
+            my_variable: !lambda "return id(ha_hello_world_temperature).state;"
 
 wifi:
   ssid: MySSID

tests/unit_tests/test_config_validation.py

@@ -2565,6 +2565,52 @@ def test_returning_lambda_no_return() -> None:
         cv.returning_lambda(Lambda("int x = 5;"))
 
 
+def test_returning_lambda_return_only_in_comment() -> None:
+    with pytest.raises(Invalid, match="return statement"):
+        cv.returning_lambda(Lambda("// return 5;\nint x = 5;"))
+
+
+def test_returning_lambda_missing_semicolon_is_accepted() -> None:
+    """A forgotten semicolon is left for the C++ compiler to report."""
+    assert isinstance(cv.returning_lambda(Lambda("return x")), Lambda)
+
+
+@pytest.mark.parametrize(
+    ("value", "expected"),
+    [
+        ("return 5;", True),
+        ("if (x) { return x; } return 0;", True),
+        ("if (x) return 1; else return 0;", True),
+        ("switch (x) { case 0: return 1; }", True),
+        # a semicolon means code: any return keyword counts
+        ("return not x;", True),
+        ("return a and b;", True),
+        ("please return the sensor; then wait", True),
+        # a forgotten semicolon is still lambda source; the compiler reports it
+        ("return id(x).state", True),
+        ("return x", True),
+        ("return 5", True),
+        ("return not x", True),
+        # accepted: a one-word tail is indistinguishable from 'return x'
+        ("return soon", True),
+        ("Alert: return home", True),
+        ("static value", False),
+        ("no returns here", False),
+        ("the_return_value", False),
+        # without a semicolon, prose is not lambda source
+        ("please return the item", False),
+        ("return to sender", False),
+        ("return a and b", False),
+        # return only inside a comment is not a return statement
+        ("// return 5;\nint x = 5;", False),
+        ("/* return 5; */ int x = 5;", False),
+        ("return 5; // done", True),
+    ],
+)
+def test_looks_like_returning_lambda(value: str, expected: bool) -> None:
+    assert cv.looks_like_returning_lambda(value) is expected
+
+
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