Fix slave id equal to 0 (#136263)

Co-authored-by: J. Nick Koston <nick@koston.org>

homeassistant/components/modbus/entity.py

@@ -80,7 +80,10 @@ class BasePlatform(Entity):
         """Initialize the Modbus binary sensor."""
 
         self._hub = hub
-        self._slave = entry.get(CONF_SLAVE) or entry.get(CONF_DEVICE_ADDRESS, 0)
+        if (conf_slave := entry.get(CONF_SLAVE)) is not None:
+            self._slave = conf_slave
+        else:
+            self._slave = entry.get(CONF_DEVICE_ADDRESS, 1)
         self._address = int(entry[CONF_ADDRESS])
         self._input_type = entry[CONF_INPUT_TYPE]
         self._value: str | None = None

homeassistant/components/modbus/modbus.py

@@ -378,7 +378,9 @@ class ModbusHub:
         self, slave: int | None, address: int, value: int | list[int], use_call: str
     ) -> ModbusPDU | None:
         """Call sync. pymodbus."""
-        kwargs: dict[str, Any] = {"slave": slave} if slave else {}
+        kwargs: dict[str, Any] = (
+            {ATTR_SLAVE: slave} if slave is not None else {ATTR_SLAVE: 1}
+        )
         entry = self._pb_request[use_call]
         kwargs[entry.value_attr_name] = value
         try:

tests/components/modbus/test_init.py

@@ -1274,3 +1274,56 @@ async def test_no_entities(hass: HomeAssistant) -> None:
         ]
     }
     assert await async_setup_component(hass, DOMAIN, config) is False
+
+
+@pytest.mark.parametrize(
+    ("do_config", "expected_slave_value"),
+    [
+        (
+            {
+                CONF_SENSORS: [
+                    {
+                        CONF_NAME: "dummy",
+                        CONF_ADDRESS: 1234,
+                    },
+                ],
+            },
+            1,
+        ),
+        (
+            {
+                CONF_SENSORS: [
+                    {
+                        CONF_NAME: "dummy",
+                        CONF_ADDRESS: 1234,
+                        CONF_SLAVE: 0,
+                    },
+                ],
+            },
+            0,
+        ),
+        (
+            {
+                CONF_SENSORS: [
+                    {
+                        CONF_NAME: "dummy",
+                        CONF_ADDRESS: 1234,
+                        CONF_DEVICE_ADDRESS: 6,
+                    },
+                ],
+            },
+            6,
+        ),
+    ],
+)
+async def test_check_default_slave(
+    hass: HomeAssistant,
+    mock_modbus,
+    do_config,
+    mock_do_cycle,
+    expected_slave_value: int,
+) -> None:
+    """Test default slave."""
+    assert mock_modbus.read_holding_registers.mock_calls
+    first_call = mock_modbus.read_holding_registers.mock_calls[0]
+    assert first_call.kwargs["slave"] == expected_slave_value