Fix regression in MQTT discovery (#58684)

* Fix regression in MQTT discovery

* Update test

homeassistant/components/mqtt/discovery.py

@@ -10,6 +10,7 @@ import time
 from homeassistant.const import CONF_DEVICE, CONF_PLATFORM
 from homeassistant.core import HomeAssistant
 from homeassistant.data_entry_flow import RESULT_TYPE_ABORT
+import homeassistant.helpers.config_validation as cv
 from homeassistant.helpers.dispatcher import (
     async_dispatcher_connect,
     async_dispatcher_send,
@@ -141,7 +142,9 @@ async def async_start(  # noqa: C901
                     if value[-1] == TOPIC_BASE and key.endswith("topic"):
                         payload[key] = f"{value[:-1]}{base}"
             if payload.get(CONF_AVAILABILITY):
-                for availability_conf in payload[CONF_AVAILABILITY]:
+                for availability_conf in cv.ensure_list(payload[CONF_AVAILABILITY]):
+                    if not isinstance(availability_conf, dict):
+                        continue
                     if topic := availability_conf.get(CONF_TOPIC):
                         if topic[0] == TOPIC_BASE:
                             availability_conf[CONF_TOPIC] = f"{base}{topic[1:]}"

tests/components/mqtt/test_discovery.py

@@ -504,6 +504,76 @@ async def test_discovery_expansion(hass, mqtt_mock, caplog):
     assert state.state == STATE_UNAVAILABLE
 
 
+async def test_discovery_expansion_2(hass, mqtt_mock, caplog):
+    """Test expansion of abbreviated discovery payload."""
+    data = (
+        '{ "~": "some/base/topic",'
+        '  "name": "DiscoveryExpansionTest1",'
+        '  "stat_t": "test_topic/~",'
+        '  "cmd_t": "~/test_topic",'
+        '  "availability": {'
+        '    "topic":"~/avail_item1",'
+        '    "payload_available": "available",'
+        '    "payload_not_available": "not_available"'
+        "  },"
+        '  "dev":{'
+        '    "ids":["5706DF"],'
+        '    "name":"DiscoveryExpansionTest1 Device",'
+        '    "mdl":"Generic",'
+        '    "sw":"1.2.3.4",'
+        '    "mf":"None",'
+        '    "sa":"default_area"'
+        "  }"
+        "}"
+    )
+
+    async_fire_mqtt_message(hass, "homeassistant/switch/bla/config", data)
+    await hass.async_block_till_done()
+
+    state = hass.states.get("switch.DiscoveryExpansionTest1")
+    assert state.state == STATE_UNAVAILABLE
+
+    async_fire_mqtt_message(hass, "some/base/topic/avail_item1", "available")
+    await hass.async_block_till_done()
+
+    state = hass.states.get("switch.DiscoveryExpansionTest1")
+    assert state is not None
+    assert state.name == "DiscoveryExpansionTest1"
+    assert ("switch", "bla") in hass.data[ALREADY_DISCOVERED]
+    assert state.state == STATE_OFF
+
+
+@pytest.mark.no_fail_on_log_exception
+async def test_discovery_expansion_3(hass, mqtt_mock, caplog):
+    """Test expansion of broken discovery payload."""
+    data = (
+        '{ "~": "some/base/topic",'
+        '  "name": "DiscoveryExpansionTest1",'
+        '  "stat_t": "test_topic/~",'
+        '  "cmd_t": "~/test_topic",'
+        '  "availability": "incorrect",'
+        '  "dev":{'
+        '    "ids":["5706DF"],'
+        '    "name":"DiscoveryExpansionTest1 Device",'
+        '    "mdl":"Generic",'
+        '    "sw":"1.2.3.4",'
+        '    "mf":"None",'
+        '    "sa":"default_area"'
+        "  }"
+        "}"
+    )
+
+    async_fire_mqtt_message(hass, "homeassistant/switch/bla/config", data)
+    await hass.async_block_till_done()
+    assert hass.states.get("switch.DiscoveryExpansionTest1") is None
+    # Make sure the malformed availability data does not trip up discovery by asserting
+    # there are schema valdiation errors in the log
+    assert (
+        "voluptuous.error.MultipleInvalid: expected a dictionary @ data['availability'][0]"
+        in caplog.text
+    )
+
+
 ABBREVIATIONS_WHITE_LIST = [
     # MQTT client/server/trigger settings
     "CONF_BIRTH_MESSAGE",