[wifi] Defer ESP8266 listener callbacks to main loop to fix stack overflow

Co-authored-by: pre-commit-ci-lite[bot] <117423508+pre-commit-ci-lite[bot]@users.noreply.github.com>
Co-authored-by: Jonathan Swoboda <154711427+swoboda1337@users.noreply.github.com>
Co-authored-by: J. Nick Koston <nick@home-assistant.io>

.clang-tidy.hash

@@ -1 +1 @@
-cf3d341206b4184ec8b7fe85141aef4fe4696aa720c3f8a06d4e57930574bdab
+069fa9526c52f7c580a9ec17c7678d12f142221387e9b561c18f95394d4629a3

esphome/components/esp32/__init__.py

@@ -1329,6 +1329,10 @@ async def to_code(config):
     # Disable dynamic log level control to save memory
     add_idf_sdkconfig_option("CONFIG_LOG_DYNAMIC_LEVEL_CONTROL", False)
 
+    # Disable per-tag log level filtering since dynamic level control is disabled above
+    # This saves ~250 bytes of RAM (tag cache) and associated code
+    add_idf_sdkconfig_option("CONFIG_LOG_TAG_LEVEL_IMPL_NONE", True)
+
     # Reduce PHY TX power in the event of a brownout
     add_idf_sdkconfig_option("CONFIG_ESP_PHY_REDUCE_TX_POWER", True)
 

esphome/components/i2c/i2c.cpp

@@ -11,12 +11,6 @@ namespace i2c {
 static const char *const TAG = "i2c";
 
 void I2CBus::i2c_scan_() {
-  // suppress logs from the IDF I2C library during the scan
-#if defined(USE_ESP32) && defined(USE_LOGGER)
-  auto previous = esp_log_level_get("*");
-  esp_log_level_set("*", ESP_LOG_NONE);
-#endif
-
   for (uint8_t address = 8; address != 120; address++) {
     auto err = write_readv(address, nullptr, 0, nullptr, 0);
     if (err == ERROR_OK) {
@@ -27,9 +21,6 @@ void I2CBus::i2c_scan_() {
     // it takes 16sec to scan on nrf52. It prevents board reset.
     arch_feed_wdt();
   }
-#if defined(USE_ESP32) && defined(USE_LOGGER)
-  esp_log_level_set("*", previous);
-#endif
 }
 
 ErrorCode I2CDevice::read_register(uint8_t a_register, uint8_t *data, size_t len) {

esphome/components/logger/logger_esp32.cpp

@@ -114,9 +114,6 @@ void Logger::pre_setup() {
 
   global_logger = this;
   esp_log_set_vprintf(esp_idf_log_vprintf_);
-  if (ESPHOME_LOG_LEVEL >= ESPHOME_LOG_LEVEL_VERBOSE) {
-    esp_log_level_set("*", ESP_LOG_VERBOSE);
-  }
 
   ESP_LOGI(TAG, "Log initialized");
 }

esphome/components/mipi_spi/mipi_spi.cpp

@@ -1,6 +1,39 @@
 #include "mipi_spi.h"
 #include "esphome/core/log.h"
 
-namespace esphome {
-namespace mipi_spi {}  // namespace mipi_spi
-}  // namespace esphome
+namespace esphome::mipi_spi {
+
+void internal_dump_config(const char *model, int width, int height, int offset_width, int offset_height, uint8_t madctl,
+                          bool invert_colors, int display_bits, bool is_big_endian, const optional<uint8_t> &brightness,
+                          GPIOPin *cs, GPIOPin *reset, GPIOPin *dc, int spi_mode, uint32_t data_rate, int bus_width) {
+  ESP_LOGCONFIG(TAG,
+                "MIPI_SPI Display\n"
+                "  Model: %s\n"
+                "  Width: %d\n"
+                "  Height: %d\n"
+                "  Swap X/Y: %s\n"
+                "  Mirror X: %s\n"
+                "  Mirror Y: %s\n"
+                "  Invert colors: %s\n"
+                "  Color order: %s\n"
+                "  Display pixels: %d bits\n"
+                "  Endianness: %s\n"
+                "  SPI Mode: %d\n"
+                "  SPI Data rate: %uMHz\n"
+                "  SPI Bus width: %d",
+                model, width, height, YESNO(madctl & MADCTL_MV), YESNO(madctl & (MADCTL_MX | MADCTL_XFLIP)),
+                YESNO(madctl & (MADCTL_MY | MADCTL_YFLIP)), YESNO(invert_colors), (madctl & MADCTL_BGR) ? "BGR" : "RGB",
+                display_bits, is_big_endian ? "Big" : "Little", spi_mode, static_cast<unsigned>(data_rate / 1000000),
+                bus_width);
+  LOG_PIN("  CS Pin: ", cs);
+  LOG_PIN("  Reset Pin: ", reset);
+  LOG_PIN("  DC Pin: ", dc);
+  if (offset_width != 0)
+    ESP_LOGCONFIG(TAG, "  Offset width: %d", offset_width);
+  if (offset_height != 0)
+    ESP_LOGCONFIG(TAG, "  Offset height: %d", offset_height);
+  if (brightness.has_value())
+    ESP_LOGCONFIG(TAG, "  Brightness: %u", brightness.value());
+}
+
+}  // namespace esphome::mipi_spi

esphome/components/mipi_spi/mipi_spi.h

@@ -63,6 +63,11 @@ enum BusType {
   BUS_TYPE_SINGLE_16 = 16,  // Single bit bus, but 16 bits per transfer
 };
 
+// Helper function for dump_config - defined in mipi_spi.cpp to allow use of LOG_PIN macro
+void internal_dump_config(const char *model, int width, int height, int offset_width, int offset_height, uint8_t madctl,
+                          bool invert_colors, int display_bits, bool is_big_endian, const optional<uint8_t> &brightness,
+                          GPIOPin *cs, GPIOPin *reset, GPIOPin *dc, int spi_mode, uint32_t data_rate, int bus_width);
+
 /**
  * Base class for MIPI SPI displays.
  * All the methods are defined here in the header file, as it is not possible to define templated methods in a cpp file.
@@ -201,37 +206,9 @@ class MipiSpi : public display::Display,
   }
 
   void dump_config() override {
-    esph_log_config(TAG,
-                    "MIPI_SPI Display\n"
-                    "  Model: %s\n"
-                    "  Width: %u\n"
-                    "  Height: %u",
-                    this->model_, WIDTH, HEIGHT);
-    if constexpr (OFFSET_WIDTH != 0)
-      esph_log_config(TAG, "  Offset width: %u", OFFSET_WIDTH);
-    if constexpr (OFFSET_HEIGHT != 0)
-      esph_log_config(TAG, "  Offset height: %u", OFFSET_HEIGHT);
-    esph_log_config(TAG,
-                    "  Swap X/Y: %s\n"
-                    "  Mirror X: %s\n"
-                    "  Mirror Y: %s\n"
-                    "  Invert colors: %s\n"
-                    "  Color order: %s\n"
-                    "  Display pixels: %d bits\n"
-                    "  Endianness: %s\n",
-                    YESNO(this->madctl_ & MADCTL_MV), YESNO(this->madctl_ & (MADCTL_MX | MADCTL_XFLIP)),
-                    YESNO(this->madctl_ & (MADCTL_MY | MADCTL_YFLIP)), YESNO(this->invert_colors_),
-                    this->madctl_ & MADCTL_BGR ? "BGR" : "RGB", DISPLAYPIXEL * 8, IS_BIG_ENDIAN ? "Big" : "Little");
-    if (this->brightness_.has_value())
-      esph_log_config(TAG, "  Brightness: %u", this->brightness_.value());
-    log_pin(TAG, "  CS Pin: ", this->cs_);
-    log_pin(TAG, "  Reset Pin: ", this->reset_pin_);
-    log_pin(TAG, "  DC Pin: ", this->dc_pin_);
-    esph_log_config(TAG,
-                    "  SPI Mode: %d\n"
-                    "  SPI Data rate: %dMHz\n"
-                    "  SPI Bus width: %d",
-                    this->mode_, static_cast<unsigned>(this->data_rate_ / 1000000), BUS_TYPE);
+    internal_dump_config(this->model_, WIDTH, HEIGHT, OFFSET_WIDTH, OFFSET_HEIGHT, this->madctl_, this->invert_colors_,
+                         DISPLAYPIXEL * 8, IS_BIG_ENDIAN, this->brightness_, this->cs_, this->reset_pin_, this->dc_pin_,
+                         this->mode_, this->data_rate_, BUS_TYPE);
   }
 
  protected:

esphome/components/mqtt/mqtt_client.cpp

@@ -643,10 +643,34 @@ static bool topic_match(const char *message, const char *subscription) {
 }
 
 void MQTTClientComponent::on_message(const std::string &topic, const std::string &payload) {
-  for (auto &subscription : this->subscriptions_) {
-    if (topic_match(topic.c_str(), subscription.topic.c_str()))
-      subscription.callback(topic, payload);
-  }
+#ifdef USE_ESP8266
+  // IMPORTANT: This defer is REQUIRED to prevent stack overflow crashes on ESP8266.
+  //
+  // On ESP8266, this callback is invoked directly from the lwIP/AsyncTCP network stack
+  // which runs in the "sys" context with a very limited stack (~4KB). By the time we
+  // reach this function, the stack is already partially consumed by the network
+  // processing chain: tcp_input -> AsyncClient::_recv -> AsyncMqttClient::_onMessage -> here.
+  //
+  // MQTT subscription callbacks can trigger arbitrary user actions (automations, HTTP
+  // requests, sensor updates, etc.) which may have deep call stacks of their own.
+  // For example, an HTTP request action requires: DNS lookup -> TCP connect -> TLS
+  // handshake (if HTTPS) -> request formatting. This easily overflows the remaining
+  // system stack space, causing a LoadStoreAlignmentCause exception or silent corruption.
+  //
+  // By deferring to the main loop, we ensure callbacks execute with a fresh, full-size
+  // stack in the normal application context rather than the constrained network task.
+  //
+  // DO NOT REMOVE THIS DEFER without understanding the above. It may appear to work
+  // in simple tests but will cause crashes with complex automations.
+  this->defer([this, topic, payload]() {
+#endif
+    for (auto &subscription : this->subscriptions_) {
+      if (topic_match(topic.c_str(), subscription.topic.c_str()))
+        subscription.callback(topic, payload);
+    }
+#ifdef USE_ESP8266
+  });
+#endif
 }
 
 // Setters

esphome/components/pmsx003/pmsx003.cpp

@@ -181,17 +181,20 @@ optional<bool> PMSX003Component::check_byte_() {
 bool PMSX003Component::check_payload_length_(uint16_t payload_length) {
   // https://avaldebe.github.io/PyPMS/sensors/Plantower/
   switch (this->type_) {
-    case Type::PMSX003:
-      // The expected payload length is typically 28 bytes.
-      // However, a 20-byte payload check was already present in the code.
-      // No official documentation was found confirming this.
-      // Retaining this check to avoid breaking existing behavior.
+    case Type::PMS1003:
+      return payload_length == 28;  // 2*13+2
+    case Type::PMS3003:             // Data 7/8/9 not set/reserved
+      return payload_length == 20;  // 2*9+2
+    case Type::PMSX003:             // Data 13 not set/reserved
+      // Deprecated: Length 20 is for PMS3003 backwards compatibility
       return payload_length == 28 || payload_length == 20;  // 2*13+2
     case Type::PMS5003S:
-    case Type::PMS5003T:
-      return payload_length == 28;  // 2*13+2 (Data 13 not set/reserved)
-    case Type::PMS5003ST:
-      return payload_length == 36;  // 2*17+2 (Data 16 not set/reserved)
+    case Type::PMS5003T:            // Data 13 not set/reserved
+      return payload_length == 28;  // 2*13+2
+    case Type::PMS5003ST:           // Data 16 not set/reserved
+      return payload_length == 36;  // 2*17+2
+    case Type::PMS9003M:
+      return payload_length == 28;  // 2*13+2
   }
   return false;
 }
@@ -314,9 +317,10 @@ void PMSX003Component::parse_data_() {
   }
 
   // Firmware Version and Error Code
-  if (this->type_ == Type::PMS5003ST) {
-    const uint8_t firmware_version = this->data_[36];
-    const uint8_t error_code = this->data_[37];
+  if (this->type_ == Type::PMS1003 || this->type_ == Type::PMS5003ST || this->type_ == Type::PMS9003M) {
+    const uint8_t firmware_error_code_offset = (this->type_ == Type::PMS5003ST) ? 36 : 28;
+    const uint8_t firmware_version = this->data_[firmware_error_code_offset];
+    const uint8_t error_code = this->data_[firmware_error_code_offset + 1];
 
     ESP_LOGD(TAG, "Got Firmware Version: 0x%02X, Error Code: 0x%02X", firmware_version, error_code);
   }

esphome/components/pmsx003/pmsx003.h

@@ -8,10 +8,13 @@
 namespace esphome::pmsx003 {
 
 enum class Type : uint8_t {
-  PMSX003 = 0,
+  PMS1003 = 0,
+  PMS3003,
+  PMSX003,  // PMS5003, PMS6003, PMS7003, PMSA003 (NOT PMSA003I - see `pmsa003i` component)
   PMS5003S,
   PMS5003T,
   PMS5003ST,
+  PMS9003M,
 };
 
 enum class Command : uint8_t {

esphome/components/pmsx003/sensor.py

@@ -40,33 +40,127 @@ pmsx003_ns = cg.esphome_ns.namespace("pmsx003")
 PMSX003Component = pmsx003_ns.class_("PMSX003Component", uart.UARTDevice, cg.Component)
 PMSX003Sensor = pmsx003_ns.class_("PMSX003Sensor", sensor.Sensor)
 
-TYPE_PMSX003 = "PMSX003"
+TYPE_PMS1003 = "PMS1003"
+TYPE_PMS3003 = "PMS3003"
+TYPE_PMSX003 = "PMSX003"  # PMS5003, PMS6003, PMS7003, PMSA003 (NOT PMSA003I - see `pmsa003i` component)
 TYPE_PMS5003S = "PMS5003S"
 TYPE_PMS5003T = "PMS5003T"
 TYPE_PMS5003ST = "PMS5003ST"
+TYPE_PMS9003M = "PMS9003M"
 
 Type = pmsx003_ns.enum("Type", is_class=True)
 
 PMSX003_TYPES = {
+    TYPE_PMS1003: Type.PMS1003,
+    TYPE_PMS3003: Type.PMS3003,
     TYPE_PMSX003: Type.PMSX003,
     TYPE_PMS5003S: Type.PMS5003S,
     TYPE_PMS5003T: Type.PMS5003T,
     TYPE_PMS5003ST: Type.PMS5003ST,
+    TYPE_PMS9003M: Type.PMS9003M,
 }
 
 SENSORS_TO_TYPE = {
-    CONF_PM_1_0_STD: [TYPE_PMSX003, TYPE_PMS5003S, TYPE_PMS5003T, TYPE_PMS5003ST],
-    CONF_PM_2_5_STD: [TYPE_PMSX003, TYPE_PMS5003S, TYPE_PMS5003T, TYPE_PMS5003ST],
-    CONF_PM_10_0_STD: [TYPE_PMSX003, TYPE_PMS5003S, TYPE_PMS5003T, TYPE_PMS5003ST],
-    CONF_PM_1_0: [TYPE_PMSX003, TYPE_PMS5003S, TYPE_PMS5003T, TYPE_PMS5003ST],
-    CONF_PM_2_5: [TYPE_PMSX003, TYPE_PMS5003S, TYPE_PMS5003T, TYPE_PMS5003ST],
-    CONF_PM_10_0: [TYPE_PMSX003, TYPE_PMS5003S, TYPE_PMS5003T, TYPE_PMS5003ST],
-    CONF_PM_0_3UM: [TYPE_PMSX003, TYPE_PMS5003S, TYPE_PMS5003T, TYPE_PMS5003ST],
-    CONF_PM_0_5UM: [TYPE_PMSX003, TYPE_PMS5003S, TYPE_PMS5003T, TYPE_PMS5003ST],
-    CONF_PM_1_0UM: [TYPE_PMSX003, TYPE_PMS5003S, TYPE_PMS5003T, TYPE_PMS5003ST],
-    CONF_PM_2_5UM: [TYPE_PMSX003, TYPE_PMS5003S, TYPE_PMS5003T, TYPE_PMS5003ST],
-    CONF_PM_5_0UM: [TYPE_PMSX003, TYPE_PMS5003S, TYPE_PMS5003ST],
-    CONF_PM_10_0UM: [TYPE_PMSX003, TYPE_PMS5003S, TYPE_PMS5003ST],
+    CONF_PM_1_0_STD: [
+        TYPE_PMS1003,
+        TYPE_PMS3003,
+        TYPE_PMSX003,
+        TYPE_PMS5003S,
+        TYPE_PMS5003T,
+        TYPE_PMS5003ST,
+        TYPE_PMS9003M,
+    ],
+    CONF_PM_2_5_STD: [
+        TYPE_PMS1003,
+        TYPE_PMS3003,
+        TYPE_PMSX003,
+        TYPE_PMS5003S,
+        TYPE_PMS5003T,
+        TYPE_PMS5003ST,
+        TYPE_PMS9003M,
+    ],
+    CONF_PM_10_0_STD: [
+        TYPE_PMS1003,
+        TYPE_PMS3003,
+        TYPE_PMSX003,
+        TYPE_PMS5003S,
+        TYPE_PMS5003T,
+        TYPE_PMS5003ST,
+        TYPE_PMS9003M,
+    ],
+    CONF_PM_1_0: [
+        TYPE_PMS1003,
+        TYPE_PMS3003,
+        TYPE_PMSX003,
+        TYPE_PMS5003S,
+        TYPE_PMS5003T,
+        TYPE_PMS5003ST,
+        TYPE_PMS9003M,
+    ],
+    CONF_PM_2_5: [
+        TYPE_PMS1003,
+        TYPE_PMS3003,
+        TYPE_PMSX003,
+        TYPE_PMS5003S,
+        TYPE_PMS5003T,
+        TYPE_PMS5003ST,
+        TYPE_PMS9003M,
+    ],
+    CONF_PM_10_0: [
+        TYPE_PMS1003,
+        TYPE_PMS3003,
+        TYPE_PMSX003,
+        TYPE_PMS5003S,
+        TYPE_PMS5003T,
+        TYPE_PMS5003ST,
+        TYPE_PMS9003M,
+    ],
+    CONF_PM_0_3UM: [
+        TYPE_PMS1003,
+        TYPE_PMSX003,
+        TYPE_PMS5003S,
+        TYPE_PMS5003T,
+        TYPE_PMS5003ST,
+        TYPE_PMS9003M,
+    ],
+    CONF_PM_0_5UM: [
+        TYPE_PMS1003,
+        TYPE_PMSX003,
+        TYPE_PMS5003S,
+        TYPE_PMS5003T,
+        TYPE_PMS5003ST,
+        TYPE_PMS9003M,
+    ],
+    CONF_PM_1_0UM: [
+        TYPE_PMS1003,
+        TYPE_PMSX003,
+        TYPE_PMS5003S,
+        TYPE_PMS5003T,
+        TYPE_PMS5003ST,
+        TYPE_PMS9003M,
+    ],
+    CONF_PM_2_5UM: [
+        TYPE_PMS1003,
+        TYPE_PMSX003,
+        TYPE_PMS5003S,
+        TYPE_PMS5003T,
+        TYPE_PMS5003ST,
+        TYPE_PMS9003M,
+    ],
+    CONF_PM_5_0UM: [
+        TYPE_PMS1003,
+        TYPE_PMSX003,
+        TYPE_PMS5003S,
+        TYPE_PMS5003ST,
+        TYPE_PMS9003M,
+    ],
+    CONF_PM_10_0UM: [
+        TYPE_PMS1003,
+        TYPE_PMSX003,
+        TYPE_PMS5003S,
+        TYPE_PMS5003ST,
+        TYPE_PMS9003M,
+    ],
     CONF_FORMALDEHYDE: [TYPE_PMS5003S, TYPE_PMS5003ST],
     CONF_TEMPERATURE: [TYPE_PMS5003T, TYPE_PMS5003ST],
     CONF_HUMIDITY: [TYPE_PMS5003T, TYPE_PMS5003ST],

esphome/components/udp/__init__.py

@@ -12,8 +12,8 @@ from esphome.components.packet_transport import (
 )
 import esphome.config_validation as cv
 from esphome.const import CONF_DATA, CONF_ID, CONF_PORT, CONF_TRIGGER_ID
-from esphome.core import ID, Lambda
-from esphome.cpp_generator import ExpressionStatement, MockObj
+from esphome.core import ID
+from esphome.cpp_generator import literal
 
 CODEOWNERS = ["@clydebarrow"]
 DEPENDENCIES = ["network"]
@@ -24,6 +24,8 @@ udp_ns = cg.esphome_ns.namespace("udp")
 UDPComponent = udp_ns.class_("UDPComponent", cg.Component)
 UDPWriteAction = udp_ns.class_("UDPWriteAction", automation.Action)
 trigger_args = cg.std_vector.template(cg.uint8)
+trigger_argname = "data"
+trigger_argtype = [(trigger_args, trigger_argname)]
 
 CONF_ADDRESSES = "addresses"
 CONF_LISTEN_ADDRESS = "listen_address"
@@ -111,13 +113,14 @@ async def to_code(config):
     cg.add(var.set_addresses([str(addr) for addr in config[CONF_ADDRESSES]]))
     if on_receive := config.get(CONF_ON_RECEIVE):
         on_receive = on_receive[0]
-        trigger = cg.new_Pvariable(on_receive[CONF_TRIGGER_ID])
+        trigger_id = cg.new_Pvariable(on_receive[CONF_TRIGGER_ID])
         trigger = await automation.build_automation(
-            trigger, [(trigger_args, "data")], on_receive
+            trigger_id, trigger_argtype, on_receive
         )
-        trigger = Lambda(str(ExpressionStatement(trigger.trigger(MockObj("data")))))
-        trigger = await cg.process_lambda(trigger, [(trigger_args, "data")])
-        cg.add(var.add_listener(trigger))
+        trigger_lambda = await cg.process_lambda(
+            trigger.trigger(literal(trigger_argname)), trigger_argtype
+        )
+        cg.add(var.add_listener(trigger_lambda))
         cg.add(var.set_should_listen())
 
 

esphome/components/usb_cdc_acm/usb_cdc_acm_esp32.cpp

@@ -155,8 +155,9 @@ void USBCDCACMInstance::setup() {
     return;
   }
 
-  // Use a larger stack size for (very) verbose logging
-  const size_t stack_size = esp_log_level_get(TAG) > ESP_LOG_DEBUG ? USB_TX_TASK_STACK_SIZE_VV : USB_TX_TASK_STACK_SIZE;
+  // Use a larger stack size for very verbose logging
+  constexpr size_t stack_size =
+      ESPHOME_LOG_LEVEL >= ESPHOME_LOG_LEVEL_VERY_VERBOSE ? USB_TX_TASK_STACK_SIZE_VV : USB_TX_TASK_STACK_SIZE;
 
   // Create a simple, unique task name per interface
   char task_name[] = "usb_tx_0";

esphome/components/web_server_base/__init__.py

@@ -53,4 +53,4 @@ async def to_code(config):
                 "lib_ignore", ["ESPAsyncTCP", "AsyncTCP", "AsyncTCP_RP2040W"]
             )
         # https://github.com/ESP32Async/ESPAsyncWebServer/blob/main/library.json
-        cg.add_library("ESP32Async/ESPAsyncWebServer", "3.9.5")
+        cg.add_library("ESP32Async/ESPAsyncWebServer", "3.9.6")

esphome/components/wifi/wifi_component.cpp

@@ -643,7 +643,7 @@ void WiFiComponent::restart_adapter() {
   // through start_connecting() first. Without this clear, stale errors would
   // trigger spurious "failed (callback)" logs. The canonical clear location
   // is in start_connecting(); this is the only exception to that pattern.
-  this->error_from_callback_ = false;
+  this->error_from_callback_ = 0;
 }
 
 void WiFiComponent::loop() {
@@ -1063,7 +1063,7 @@ void WiFiComponent::start_connecting(const WiFiAP &ap) {
   // This is the canonical location for clearing the flag since all connection
   // attempts go through start_connecting(). The only other clear is in
   // restart_adapter() which enters COOLDOWN without calling start_connecting().
-  this->error_from_callback_ = false;
+  this->error_from_callback_ = 0;
 
   if (!this->wifi_sta_connect_(ap)) {
     ESP_LOGE(TAG, "wifi_sta_connect_ failed");
@@ -1468,7 +1468,11 @@ void WiFiComponent::check_connecting_finished(uint32_t now) {
   }
 
   if (this->error_from_callback_) {
+    // ESP8266: logging done in callback, listeners deferred via pending_.disconnect
+    // Other platforms: just log generic failure message
+#ifndef USE_ESP8266
     ESP_LOGW(TAG, "Connecting to network failed (callback)");
+#endif
     this->retry_connect();
     return;
   }

esphome/components/wifi/wifi_component.h

@@ -58,6 +58,12 @@ static constexpr int8_t WIFI_RSSI_DISCONNECTED = -127;
 /// Buffer size for SSID (IEEE 802.11 max 32 bytes + null terminator)
 static constexpr size_t SSID_BUFFER_SIZE = 33;
 
+#ifdef USE_ESP8266
+/// Special disconnect reason for authmode downgrade (CVE-2020-12638 mitigation)
+/// Not a real WiFi reason code - used internally for deferred logging
+static constexpr uint8_t WIFI_DISCONNECT_REASON_AUTHMODE_DOWNGRADE = 254;
+#endif
+
 struct SavedWifiSettings {
   char ssid[33];
   char password[65];
@@ -590,6 +596,9 @@ class WiFiComponent : public Component {
   void connect_soon_();
 
   void wifi_loop_();
+#ifdef USE_ESP8266
+  void process_pending_callbacks_();
+#endif
   bool wifi_mode_(optional<bool> sta, optional<bool> ap);
   bool wifi_sta_pre_setup_();
   bool wifi_apply_output_power_(float output_power);
@@ -704,10 +713,26 @@ class WiFiComponent : public Component {
   uint8_t num_ipv6_addresses_{0};
 #endif /* USE_NETWORK_IPV6 */
 
+  // 0 = no error, non-zero = disconnect reason code from callback
+  // This serves as both the error flag and stores the reason for deferred logging
+  uint8_t error_from_callback_{0};
+
+#ifdef USE_ESP8266
+  // Pending listener callbacks from system context (ESP8266 only)
+  // ESP8266 callbacks run in SDK system context with ~2KB stack where
+  // calling arbitrary listener callbacks is unsafe. These flags defer
+  // listener notifications to wifi_loop_() which runs with full stack.
+  struct {
+    bool connect : 1;        // STA connected, notify listeners
+    bool disconnect : 1;     // STA disconnected, notify listeners
+    bool got_ip : 1;         // Got IP, notify listeners
+    bool scan_complete : 1;  // Scan complete, notify listeners
+  } pending_{};
+#endif
+
   // Group all boolean values together
   bool has_ap_{false};
   bool handled_connected_state_{false};
-  bool error_from_callback_{false};
   bool scan_done_{false};
   bool ap_setup_{false};
   bool ap_started_{false};

esphome/components/wifi/wifi_component_esp8266.cpp

@@ -511,21 +511,8 @@ void WiFiComponent::wifi_event_callback(System_Event_t *event) {
                it.channel);
 #endif
       s_sta_connected = true;
-#ifdef USE_WIFI_CONNECT_STATE_LISTENERS
-      for (auto *listener : global_wifi_component->connect_state_listeners_) {
-        listener->on_wifi_connect_state(StringRef(it.ssid, it.ssid_len), it.bssid);
-      }
-#endif
-      // For static IP configurations, GOT_IP event may not fire, so notify IP listeners here
-#if defined(USE_WIFI_IP_STATE_LISTENERS) && defined(USE_WIFI_MANUAL_IP)
-      if (const WiFiAP *config = global_wifi_component->get_selected_sta_();
-          config && config->get_manual_ip().has_value()) {
-        for (auto *listener : global_wifi_component->ip_state_listeners_) {
-          listener->on_ip_state(global_wifi_component->wifi_sta_ip_addresses(),
-                                global_wifi_component->get_dns_address(0), global_wifi_component->get_dns_address(1));
-        }
-      }
-#endif
+      // Defer listener callbacks to main loop - system context has limited stack
+      global_wifi_component->pending_.connect = true;
       break;
     }
     case EVENT_STAMODE_DISCONNECTED: {
@@ -543,17 +530,9 @@ void WiFiComponent::wifi_event_callback(System_Event_t *event) {
       }
       s_sta_connected = false;
       s_sta_connecting = false;
-      // IMPORTANT: Set error flag BEFORE notifying listeners.
-      // This ensures is_connected() returns false during listener callbacks,
-      // which is critical for proper reconnection logic (e.g., roaming).
-      global_wifi_component->error_from_callback_ = true;
-#ifdef USE_WIFI_CONNECT_STATE_LISTENERS
-      // Notify listeners AFTER setting error flag so they see correct state
-      static constexpr uint8_t EMPTY_BSSID[6] = {};
-      for (auto *listener : global_wifi_component->connect_state_listeners_) {
-        listener->on_wifi_connect_state(StringRef(), EMPTY_BSSID);
-      }
-#endif
+      // Store reason as error flag; defer listener callbacks to main loop
+      global_wifi_component->error_from_callback_ = it.reason;
+      global_wifi_component->pending_.disconnect = true;
       break;
     }
     case EVENT_STAMODE_AUTHMODE_CHANGE: {
@@ -564,10 +543,8 @@ void WiFiComponent::wifi_event_callback(System_Event_t *event) {
       // https://lbsfilm.at/blog/wpa2-authenticationmode-downgrade-in-espressif-microprocessors
       if (it.old_mode != AUTH_OPEN && it.new_mode == AUTH_OPEN) {
         ESP_LOGW(TAG, "Potential Authmode downgrade detected, disconnecting");
-        // we can't call retry_connect() from this context, so disconnect immediately
-        // and notify main thread with error_from_callback_
         wifi_station_disconnect();
-        global_wifi_component->error_from_callback_ = true;
+        global_wifi_component->error_from_callback_ = WIFI_DISCONNECT_REASON_AUTHMODE_DOWNGRADE;
       }
       break;
     }
@@ -578,12 +555,8 @@ void WiFiComponent::wifi_event_callback(System_Event_t *event) {
       ESP_LOGV(TAG, "static_ip=%s gateway=%s netmask=%s", network::IPAddress(&it.ip).str_to(ip_buf),
                network::IPAddress(&it.gw).str_to(gw_buf), network::IPAddress(&it.mask).str_to(mask_buf));
       s_sta_got_ip = true;
-#ifdef USE_WIFI_IP_STATE_LISTENERS
-      for (auto *listener : global_wifi_component->ip_state_listeners_) {
-        listener->on_ip_state(global_wifi_component->wifi_sta_ip_addresses(), global_wifi_component->get_dns_address(0),
-                              global_wifi_component->get_dns_address(1));
-      }
-#endif
+      // Defer listener callbacks to main loop - system context has limited stack
+      global_wifi_component->pending_.got_ip = true;
       break;
     }
     case EVENT_STAMODE_DHCP_TIMEOUT: {
@@ -793,11 +766,7 @@ void WiFiComponent::wifi_scan_done_callback_(void *arg, STATUS status) {
   ESP_LOGV(TAG, "Scan complete: %zu found, %zu stored%s", total, this->scan_result_.size(),
            needs_full ? "" : " (filtered)");
   this->scan_done_ = true;
-#ifdef USE_WIFI_SCAN_RESULTS_LISTENERS
-  for (auto *listener : global_wifi_component->scan_results_listeners_) {
-    listener->on_wifi_scan_results(global_wifi_component->scan_result_);
-  }
-#endif
+  this->pending_.scan_complete = true;  // Defer listener callbacks to main loop
 }
 
 #ifdef USE_WIFI_AP
@@ -983,7 +952,59 @@ network::IPAddress WiFiComponent::wifi_gateway_ip_() {
   return network::IPAddress(&ip.gw);
 }
 network::IPAddress WiFiComponent::wifi_dns_ip_(int num) { return network::IPAddress(dns_getserver(num)); }
-void WiFiComponent::wifi_loop_() {}
+void WiFiComponent::wifi_loop_() { this->process_pending_callbacks_(); }
+
+void WiFiComponent::process_pending_callbacks_() {
+  // Notify listeners for connect event (logging already done in callback)
+  if (this->pending_.connect) {
+    this->pending_.connect = false;
+#ifdef USE_WIFI_CONNECT_STATE_LISTENERS
+    bssid_t bssid = this->wifi_bssid();
+    char ssid_buf[SSID_BUFFER_SIZE];
+    for (auto *listener : this->connect_state_listeners_) {
+      listener->on_wifi_connect_state(StringRef(this->wifi_ssid_to(ssid_buf)), bssid);
+    }
+#endif
+#if defined(USE_WIFI_IP_STATE_LISTENERS) && defined(USE_WIFI_MANUAL_IP)
+    if (const WiFiAP *config = this->get_selected_sta_(); config && config->get_manual_ip().has_value()) {
+      for (auto *listener : this->ip_state_listeners_) {
+        listener->on_ip_state(this->wifi_sta_ip_addresses(), this->get_dns_address(0), this->get_dns_address(1));
+      }
+    }
+#endif
+  }
+
+  // Notify listeners for disconnect event (logging already done in callback)
+  if (this->pending_.disconnect) {
+    this->pending_.disconnect = false;
+#ifdef USE_WIFI_CONNECT_STATE_LISTENERS
+    static constexpr uint8_t EMPTY_BSSID[6] = {};
+    for (auto *listener : this->connect_state_listeners_) {
+      listener->on_wifi_connect_state(StringRef(), EMPTY_BSSID);
+    }
+#endif
+  }
+
+  // Notify listeners for got IP event (logging already done in callback)
+  if (this->pending_.got_ip) {
+    this->pending_.got_ip = false;
+#ifdef USE_WIFI_IP_STATE_LISTENERS
+    for (auto *listener : this->ip_state_listeners_) {
+      listener->on_ip_state(this->wifi_sta_ip_addresses(), this->get_dns_address(0), this->get_dns_address(1));
+    }
+#endif
+  }
+
+  // Notify listeners for scan complete (logging already done in callback)
+  if (this->pending_.scan_complete) {
+    this->pending_.scan_complete = false;
+#ifdef USE_WIFI_SCAN_RESULTS_LISTENERS
+    for (auto *listener : this->scan_results_listeners_) {
+      listener->on_wifi_scan_results(this->scan_result_);
+    }
+#endif
+  }
+}
 
 }  // namespace esphome::wifi
 #endif

esphome/components/wifi/wifi_component_esp_idf.cpp

@@ -774,7 +774,7 @@ void WiFiComponent::wifi_process_event_(IDFWiFiEvent *data) {
     }
     s_sta_connected = false;
     s_sta_connecting = false;
-    error_from_callback_ = true;
+    error_from_callback_ = 1;
 #ifdef USE_WIFI_CONNECT_STATE_LISTENERS
     static constexpr uint8_t EMPTY_BSSID[6] = {};
     for (auto *listener : this->connect_state_listeners_) {

esphome/components/wifi/wifi_component_libretiny.cpp

@@ -494,7 +494,7 @@ void WiFiComponent::wifi_process_event_(LTWiFiEvent *event) {
                    s_ignored_disconnect_count, get_disconnect_reason_str(it.reason));
           s_sta_state = LTWiFiSTAState::ERROR_FAILED;
           WiFi.disconnect();
-          this->error_from_callback_ = true;
+          this->error_from_callback_ = 1;
           // Don't break - fall through to notify listeners
         } else {
           ESP_LOGV(TAG, "Ignoring disconnect event with empty ssid while connecting (reason=%s, count=%u)",
@@ -520,7 +520,7 @@ void WiFiComponent::wifi_process_event_(LTWiFiEvent *event) {
           reason == WIFI_REASON_NO_AP_FOUND || reason == WIFI_REASON_ASSOC_FAIL ||
           reason == WIFI_REASON_HANDSHAKE_TIMEOUT) {
         WiFi.disconnect();
-        this->error_from_callback_ = true;
+        this->error_from_callback_ = 1;
       }
 
 #ifdef USE_WIFI_CONNECT_STATE_LISTENERS
@@ -539,7 +539,7 @@ void WiFiComponent::wifi_process_event_(LTWiFiEvent *event) {
       if (it.old_mode != WIFI_AUTH_OPEN && it.new_mode == WIFI_AUTH_OPEN) {
         ESP_LOGW(TAG, "Potential Authmode downgrade detected, disconnecting");
         WiFi.disconnect();
-        this->error_from_callback_ = true;
+        this->error_from_callback_ = 1;
         s_sta_state = LTWiFiSTAState::ERROR_FAILED;
       }
       break;

esphome/core/__init__.py

@@ -278,9 +278,13 @@ LAMBDA_PROG = re.compile(r"\bid\(\s*([a-zA-Z_][a-zA-Z0-9_]*)\s*\)(\.?)")
 
 class Lambda:
     def __init__(self, value):
+        from esphome.cpp_generator import Expression, statement
+
         # pylint: disable=protected-access
         if isinstance(value, Lambda):
             self._value = value._value
+        elif isinstance(value, Expression):
+            self._value = str(statement(value))
         else:
             self._value = value
         self._parts = None

esphome/core/application.cpp

@@ -210,7 +210,7 @@ void Application::loop() {
 #ifdef USE_ESP32
       esp_chip_info_t chip_info;
       esp_chip_info(&chip_info);
-      ESP_LOGI(TAG, "ESP32 Chip: %s r%d.%d, %d core(s)", ESPHOME_VARIANT, chip_info.revision / 100,
+      ESP_LOGI(TAG, "ESP32 Chip: %s rev%d.%d, %d core(s)", ESPHOME_VARIANT, chip_info.revision / 100,
                chip_info.revision % 100, chip_info.cores);
 #if defined(USE_ESP32_VARIANT_ESP32) && !defined(USE_ESP32_MIN_CHIP_REVISION_SET)
       // Suggest optimization for chips that don't need the PSRAM cache workaround

esphome/cpp_generator.py

@@ -462,6 +462,16 @@ def statement(expression: Expression | Statement) -> Statement:
     return ExpressionStatement(expression)
 
 
+def literal(name: str) -> "MockObj":
+    """Create a literal name that will appear in the generated code
+    not surrounded by quotes.
+
+    :param name: The name of the literal.
+    :return: The literal as a MockObj.
+    """
+    return MockObj(name, "")
+
+
 def variable(
     id_: ID, rhs: SafeExpType, type_: "MockObj" = None, register=True
 ) -> "MockObj":
@@ -665,7 +675,7 @@ async def get_variable_with_full_id(id_: ID) -> tuple[ID, "MockObj"]:
 
 
 async def process_lambda(
-    value: Lambda,
+    value: Lambda | Expression,
     parameters: TemplateArgsType,
     capture: str = "",
     return_type: SafeExpType = None,
@@ -689,6 +699,14 @@ async def process_lambda(
 
     if value is None:
         return None
+    # Inadvertently passing a malformed parameters value will lead to the build process mysteriously hanging at the
+    # "Generating C++ source..." stage, so check here to save the developer's hair.
+    assert isinstance(parameters, list) and all(
+        isinstance(p, tuple) and len(p) == 2 for p in parameters
+    )
+    if isinstance(value, Expression):
+        value = Lambda(value)
+
     parts = value.parts[:]
     for i, id in enumerate(value.requires_ids):
         full_id, var = await get_variable_with_full_id(id)

platformio.ini

@@ -114,7 +114,7 @@ lib_deps =
     ESP8266WiFi                           ; wifi (Arduino built-in)
     Update                                ; ota (Arduino built-in)
     ESP32Async/ESPAsyncTCP@2.0.0          ; async_tcp
-    ESP32Async/ESPAsyncWebServer@3.9.5    ; web_server_base
+    ESP32Async/ESPAsyncWebServer@3.9.6    ; web_server_base
     makuna/NeoPixelBus@2.7.3              ; neopixelbus
     ESP8266HTTPClient                     ; http_request (Arduino built-in)
     ESP8266mDNS                           ; mdns (Arduino built-in)
@@ -202,7 +202,7 @@ lib_deps =
     ${common:arduino.lib_deps}
     ayushsharma82/RPAsyncTCP@1.3.2        ; async_tcp
     bblanchon/ArduinoJson@7.4.2           ; json
-    ESP32Async/ESPAsyncWebServer@3.9.5    ; web_server_base
+    ESP32Async/ESPAsyncWebServer@3.9.6    ; web_server_base
 build_flags =
     ${common:arduino.build_flags}
     -DUSE_RP2040
@@ -218,7 +218,7 @@ framework = arduino
 lib_compat_mode = soft
 lib_deps =
     bblanchon/ArduinoJson@7.4.2           ; json
-    ESP32Async/ESPAsyncWebServer@3.9.5    ; web_server_base
+    ESP32Async/ESPAsyncWebServer@3.9.6    ; web_server_base
     droscy/esp_wireguard@0.4.2            ; wireguard
 build_flags =
     ${common:arduino.build_flags}

tests/components/mipi_spi/test.esp8266-ard.yaml

@@ -0,0 +1,10 @@
+substitutions:
+  dc_pin: GPIO15
+  cs_pin: GPIO5
+  enable_pin: GPIO4
+  reset_pin: GPIO16
+
+packages:
+  spi: !include ../../test_build_components/common/spi/esp8266-ard.yaml
+
+<<: !include common.yaml

tests/unit_tests/test_cpp_generator.py

@@ -347,3 +347,280 @@ class TestMockObj:
         assert isinstance(actual, cg.MockObj)
         assert actual.base == "foo.eek"
         assert actual.op == "."
+
+
+class TestStatementFunction:
+    """Tests for the statement() function."""
+
+    def test_statement__expression_converted_to_statement(self):
+        """Test that expressions are converted to ExpressionStatement."""
+        expr = cg.RawExpression("foo()")
+        result = cg.statement(expr)
+
+        assert isinstance(result, cg.ExpressionStatement)
+        assert str(result) == "foo();"
+
+    def test_statement__statement_unchanged(self):
+        """Test that statements are returned unchanged."""
+        stmt = cg.RawStatement("foo()")
+        result = cg.statement(stmt)
+
+        assert result is stmt
+        assert str(result) == "foo()"
+
+    def test_statement__expression_statement_unchanged(self):
+        """Test that ExpressionStatement is returned unchanged."""
+        stmt = cg.ExpressionStatement(42)
+        result = cg.statement(stmt)
+
+        assert result is stmt
+        assert str(result) == "42;"
+
+    def test_statement__line_comment_unchanged(self):
+        """Test that LineComment is returned unchanged."""
+        stmt = cg.LineComment("This is a comment")
+        result = cg.statement(stmt)
+
+        assert result is stmt
+        assert str(result) == "// This is a comment"
+
+
+class TestLiteralFunction:
+    """Tests for the literal() function."""
+
+    def test_literal__creates_mockobj(self):
+        """Test that literal() creates a MockObj."""
+        result = cg.literal("MY_CONSTANT")
+
+        assert isinstance(result, cg.MockObj)
+        assert result.base == "MY_CONSTANT"
+        assert result.op == ""
+
+    def test_literal__string_representation(self):
+        """Test that literal names appear unquoted in generated code."""
+        result = cg.literal("nullptr")
+
+        assert str(result) == "nullptr"
+
+    def test_literal__can_be_used_in_expressions(self):
+        """Test that literals can be used as part of larger expressions."""
+        null_lit = cg.literal("nullptr")
+        expr = cg.CallExpression(cg.RawExpression("my_func"), null_lit)
+
+        assert str(expr) == "my_func(nullptr)"
+
+    def test_literal__common_cpp_literals(self):
+        """Test common C++ literal values."""
+        test_cases = [
+            ("nullptr", "nullptr"),
+            ("true", "true"),
+            ("false", "false"),
+            ("NULL", "NULL"),
+            ("NAN", "NAN"),
+        ]
+
+        for name, expected in test_cases:
+            result = cg.literal(name)
+            assert str(result) == expected
+
+
+class TestLambdaConstructor:
+    """Tests for the Lambda class constructor in core/__init__.py."""
+
+    def test_lambda__from_string(self):
+        """Test Lambda constructor with string argument."""
+        from esphome.core import Lambda
+
+        lambda_obj = Lambda("return x + 1;")
+
+        assert lambda_obj.value == "return x + 1;"
+        assert str(lambda_obj) == "return x + 1;"
+
+    def test_lambda__from_expression(self):
+        """Test Lambda constructor with Expression argument."""
+        from esphome.core import Lambda
+
+        expr = cg.RawExpression("x + 1")
+        lambda_obj = Lambda(expr)
+
+        # Expression should be converted to statement (with semicolon)
+        assert lambda_obj.value == "x + 1;"
+
+    def test_lambda__from_lambda(self):
+        """Test Lambda constructor with another Lambda argument."""
+        from esphome.core import Lambda
+
+        original = Lambda("return x + 1;")
+        copy = Lambda(original)
+
+        assert copy.value == original.value
+        assert copy.value == "return x + 1;"
+
+    def test_lambda__parts_parsing(self):
+        """Test that Lambda correctly parses parts with id() references."""
+        from esphome.core import Lambda
+
+        lambda_obj = Lambda("return id(my_sensor).state;")
+        parts = lambda_obj.parts
+
+        # Parts should be split by LAMBDA_PROG regex: text, id, op, text
+        assert len(parts) == 4
+        assert parts[0] == "return "
+        assert parts[1] == "my_sensor"
+        assert parts[2] == "."
+        assert parts[3] == "state;"
+
+    def test_lambda__requires_ids(self):
+        """Test that Lambda correctly extracts required IDs."""
+        from esphome.core import ID, Lambda
+
+        lambda_obj = Lambda("return id(sensor1).state + id(sensor2).value;")
+        ids = lambda_obj.requires_ids
+
+        assert len(ids) == 2
+        assert all(isinstance(id_obj, ID) for id_obj in ids)
+        assert ids[0].id == "sensor1"
+        assert ids[1].id == "sensor2"
+
+    def test_lambda__no_ids(self):
+        """Test Lambda with no id() references."""
+        from esphome.core import Lambda
+
+        lambda_obj = Lambda("return 42;")
+        ids = lambda_obj.requires_ids
+
+        assert len(ids) == 0
+
+    def test_lambda__comment_removal(self):
+        """Test that comments are removed when parsing parts."""
+        from esphome.core import Lambda
+
+        lambda_obj = Lambda("return id(sensor).state; // Get sensor state")
+        parts = lambda_obj.parts
+
+        # Comment should be replaced with space, not affect parsing
+        assert "my_sensor" not in str(parts)
+
+    def test_lambda__multiline_string(self):
+        """Test Lambda with multiline string."""
+        from esphome.core import Lambda
+
+        code = """if (id(sensor).state > 0) {
+  return true;
+}
+return false;"""
+        lambda_obj = Lambda(code)
+
+        assert lambda_obj.value == code
+        assert "sensor" in [id_obj.id for id_obj in lambda_obj.requires_ids]
+
+
+@pytest.mark.asyncio
+class TestProcessLambda:
+    """Tests for the process_lambda() async function."""
+
+    async def test_process_lambda__none_value(self):
+        """Test that None returns None."""
+        result = await cg.process_lambda(None, [])
+
+        assert result is None
+
+    async def test_process_lambda__with_expression(self):
+        """Test process_lambda with Expression argument."""
+
+        expr = cg.RawExpression("return x + 1")
+        result = await cg.process_lambda(expr, [(int, "x")])
+
+        assert isinstance(result, cg.LambdaExpression)
+        assert "x + 1" in str(result)
+
+    async def test_process_lambda__simple_lambda_no_ids(self):
+        """Test process_lambda with simple Lambda without id() references."""
+        from esphome.core import Lambda
+
+        lambda_obj = Lambda("return x + 1;")
+        result = await cg.process_lambda(lambda_obj, [(int, "x")])
+
+        assert isinstance(result, cg.LambdaExpression)
+        # Should have parameter
+        lambda_str = str(result)
+        assert "int32_t x" in lambda_str
+        assert "return x + 1;" in lambda_str
+
+    async def test_process_lambda__with_return_type(self):
+        """Test process_lambda with return type specified."""
+        from esphome.core import Lambda
+
+        lambda_obj = Lambda("return x > 0;")
+        result = await cg.process_lambda(lambda_obj, [(int, "x")], return_type=bool)
+
+        assert isinstance(result, cg.LambdaExpression)
+        lambda_str = str(result)
+        assert "-> bool" in lambda_str
+
+    async def test_process_lambda__with_capture(self):
+        """Test process_lambda with capture specified."""
+        from esphome.core import Lambda
+
+        lambda_obj = Lambda("return captured + x;")
+        result = await cg.process_lambda(lambda_obj, [(int, "x")], capture="captured")
+
+        assert isinstance(result, cg.LambdaExpression)
+        lambda_str = str(result)
+        assert "[captured]" in lambda_str
+
+    async def test_process_lambda__empty_capture(self):
+        """Test process_lambda with empty capture (stateless lambda)."""
+        from esphome.core import Lambda
+
+        lambda_obj = Lambda("return x + 1;")
+        result = await cg.process_lambda(lambda_obj, [(int, "x")], capture="")
+
+        assert isinstance(result, cg.LambdaExpression)
+        lambda_str = str(result)
+        assert "[]" in lambda_str
+
+    async def test_process_lambda__no_parameters(self):
+        """Test process_lambda with no parameters."""
+        from esphome.core import Lambda
+
+        lambda_obj = Lambda("return 42;")
+        result = await cg.process_lambda(lambda_obj, [])
+
+        assert isinstance(result, cg.LambdaExpression)
+        lambda_str = str(result)
+        # Should have empty parameter list
+        assert "()" in lambda_str
+
+    async def test_process_lambda__multiple_parameters(self):
+        """Test process_lambda with multiple parameters."""
+        from esphome.core import Lambda
+
+        lambda_obj = Lambda("return x + y + z;")
+        result = await cg.process_lambda(
+            lambda_obj, [(int, "x"), (float, "y"), (bool, "z")]
+        )
+
+        assert isinstance(result, cg.LambdaExpression)
+        lambda_str = str(result)
+        assert "int32_t x" in lambda_str
+        assert "float y" in lambda_str
+        assert "bool z" in lambda_str
+
+    async def test_process_lambda__parameter_validation(self):
+        """Test that malformed parameters raise assertion error."""
+        from esphome.core import Lambda
+
+        lambda_obj = Lambda("return x;")
+
+        # Test invalid parameter format (not list of tuples)
+        with pytest.raises(AssertionError):
+            await cg.process_lambda(lambda_obj, "invalid")
+
+        # Test invalid tuple format (not 2-element tuples)
+        with pytest.raises(AssertionError):
+            await cg.process_lambda(lambda_obj, [(int, "x", "extra")])
+
+        # Test invalid tuple format (single element)
+        with pytest.raises(AssertionError):
+            await cg.process_lambda(lambda_obj, [(int,)])