[thermostat] Allow a dry-only thermostat without cool_action (#20682)

esphome/components/thermostat/climate.py

@@ -240,12 +240,6 @@ def validate_thermostat(config: ConfigType) -> ConfigType:
             CONF_SUPPLEMENTAL_HEATING_ACTION,
             CONF_SUPPLEMENTAL_HEATING_DELTA,
         ],
-        CONF_MIN_COOLING_OFF_TIME: [
-            CONF_COOL_ACTION,
-        ],
-        CONF_MIN_COOLING_RUN_TIME: [
-            CONF_COOL_ACTION,
-        ],
         CONF_MIN_FANNING_OFF_TIME: [
             CONF_FAN_ONLY_ACTION,
         ],
@@ -284,6 +278,17 @@ def validate_thermostat(config: ConfigType) -> ConfigType:
                     f"{req_trigger} must be defined to use {config_trigger}"
                 )
 
+    # Dry mode runs on the cooling timers, so a dehumidifier needs no cool_action.
+    for timer in (CONF_MIN_COOLING_OFF_TIME, CONF_MIN_COOLING_RUN_TIME):
+        if (
+            timer in config
+            and CONF_COOL_ACTION not in config
+            and CONF_DRY_ACTION not in config
+        ):
+            raise cv.Invalid(
+                f"{CONF_COOL_ACTION} or {CONF_DRY_ACTION} must be defined to use {timer}"
+            )
+
     if CONF_FAN_ONLY_ACTION in config:
         # determine validation requirements based on fan_only_action_uses_fan_mode_timer setting
         if config[CONF_FAN_ONLY_ACTION_USES_FAN_MODE_TIMER] is True:

tests/component_tests/thermostat/config/cooling_timer_without_action.yaml

@@ -0,0 +1,27 @@
+---
+esphome:
+  name: test
+
+logger:
+
+esp32:
+  board: esp32dev
+
+sensor:
+  - platform: template
+    id: temp_sensor
+    lambda: return 21.0;
+
+climate:
+  - platform: thermostat
+    id: heater
+    name: Heater
+    sensor: temp_sensor
+    min_idle_time: 30s
+    min_heating_off_time: 300s
+    min_heating_run_time: 300s
+    min_cooling_off_time: 300s
+    heat_action:
+      - logger.log: heat
+    idle_action:
+      - logger.log: idle

tests/component_tests/thermostat/config/dry_only.yaml

@@ -0,0 +1,30 @@
+---
+esphome:
+  name: test
+
+logger:
+
+esp32:
+  board: esp32dev
+
+sensor:
+  - platform: template
+    id: temp_sensor
+    lambda: return 21.0;
+
+climate:
+  - platform: thermostat
+    id: dehumidifier
+    name: Dehumidifier
+    sensor: temp_sensor
+    min_idle_time: 0s
+    min_cooling_off_time: 0s
+    min_cooling_run_time: 0s
+    min_fanning_off_time: 0s
+    min_fanning_run_time: 0s
+    idle_action:
+      - logger.log: idle
+    fan_only_action:
+      - logger.log: fan only
+    dry_action:
+      - logger.log: dry

tests/component_tests/thermostat/test_validation.py

@@ -0,0 +1,36 @@
+"""Tests for the thermostat config validation."""
+
+from collections.abc import Callable
+from pathlib import Path
+
+import pytest
+
+from esphome.config import read_config
+from esphome.core import CORE
+
+
+def test_dry_only_config_is_valid(
+    generate_main: Callable[[str | Path], str],
+    component_config_path: Callable[[str], Path],
+) -> None:
+    """A dehumidifier has dry mode but no cool_action; dry mode uses the cooling timers."""
+    main_cpp = generate_main(component_config_path("dry_only.yaml"))
+
+    assert "dehumidifier->set_cooling_minimum_off_time_in_sec(0);" in main_cpp
+    assert "dehumidifier->set_cooling_minimum_run_time_in_sec(0);" in main_cpp
+    assert "dehumidifier->set_supports_dry(true);" in main_cpp
+    assert "dehumidifier->set_supports_cool(" not in main_cpp
+
+
+def test_cooling_timer_needs_cool_or_dry_action(
+    component_config_path: Callable[[str], Path],
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    """A cooling timer with neither cool_action nor dry_action is still rejected."""
+    CORE.config_path = component_config_path("cooling_timer_without_action.yaml")
+    assert read_config({}) is None
+    captured = capsys.readouterr()
+    assert (
+        "cool_action or dry_action must be defined to use min_cooling_off_time"
+        in captured.out
+    )