[mqtt] Use .c_str() for StringRef payloads to match non-allocating publish overload

Add _to() variants that write into a stack buffer and return StringRef,
avoiding heap allocation on every publish. Update publish_state() in
climate (11 allocations eliminated), fan (3), cover (2), and valve (1)
to use the new stack-based getters.

The allocating getters are retained for setup-time paths (subscribe,
send_discovery, dump_config) where the allocation is one-time.

esphome/components/debug/debug_esp8266.cpp

@@ -1,7 +1,6 @@
 #include "debug_component.h"
 #ifdef USE_ESP8266
 #include "esphome/core/log.h"
-#include "esphome/core/progmem.h"
 #include <Esp.h>
 
 extern "C" {
@@ -20,38 +19,27 @@ namespace debug {
 
 static const char *const TAG = "debug";
 
-// PROGMEM string table for reset reasons, indexed by reason code (0-6), with "Unknown" as fallback
-// clang-format off
-PROGMEM_STRING_TABLE(ResetReasonStrings,
-  "Power On",                  // 0 = REASON_DEFAULT_RST
-  "Hardware Watchdog",         // 1 = REASON_WDT_RST
-  "Exception",                 // 2 = REASON_EXCEPTION_RST
-  "Software Watchdog",         // 3 = REASON_SOFT_WDT_RST
-  "Software/System restart",   // 4 = REASON_SOFT_RESTART
-  "Deep-Sleep Wake",           // 5 = REASON_DEEP_SLEEP_AWAKE
-  "External System",           // 6 = REASON_EXT_SYS_RST
-  "Unknown"                    // 7 = fallback
-);
-// clang-format on
-static_assert(REASON_DEFAULT_RST == 0, "Reset reason enum values must match table indices");
-static_assert(REASON_WDT_RST == 1, "Reset reason enum values must match table indices");
-static_assert(REASON_EXCEPTION_RST == 2, "Reset reason enum values must match table indices");
-static_assert(REASON_SOFT_WDT_RST == 3, "Reset reason enum values must match table indices");
-static_assert(REASON_SOFT_RESTART == 4, "Reset reason enum values must match table indices");
-static_assert(REASON_DEEP_SLEEP_AWAKE == 5, "Reset reason enum values must match table indices");
-static_assert(REASON_EXT_SYS_RST == 6, "Reset reason enum values must match table indices");
-
-// PROGMEM string table for flash chip modes, indexed by mode code (0-3), with "UNKNOWN" as fallback
-PROGMEM_STRING_TABLE(FlashModeStrings, "QIO", "QOUT", "DIO", "DOUT", "UNKNOWN");
-static_assert(FM_QIO == 0, "Flash mode enum values must match table indices");
-static_assert(FM_QOUT == 1, "Flash mode enum values must match table indices");
-static_assert(FM_DIO == 2, "Flash mode enum values must match table indices");
-static_assert(FM_DOUT == 3, "Flash mode enum values must match table indices");
-
 // Get reset reason string from reason code (no heap allocation)
 // Returns LogString* pointing to flash (PROGMEM) on ESP8266
 static const LogString *get_reset_reason_str(uint32_t reason) {
-  return ResetReasonStrings::get_log_str(static_cast<uint8_t>(reason), ResetReasonStrings::LAST_INDEX);
+  switch (reason) {
+    case REASON_DEFAULT_RST:
+      return LOG_STR("Power On");
+    case REASON_WDT_RST:
+      return LOG_STR("Hardware Watchdog");
+    case REASON_EXCEPTION_RST:
+      return LOG_STR("Exception");
+    case REASON_SOFT_WDT_RST:
+      return LOG_STR("Software Watchdog");
+    case REASON_SOFT_RESTART:
+      return LOG_STR("Software/System restart");
+    case REASON_DEEP_SLEEP_AWAKE:
+      return LOG_STR("Deep-Sleep Wake");
+    case REASON_EXT_SYS_RST:
+      return LOG_STR("External System");
+    default:
+      return LOG_STR("Unknown");
+  }
 }
 
 // Size for core version hex buffer
@@ -104,9 +92,23 @@ size_t DebugComponent::get_device_info_(std::span<char, DEVICE_INFO_BUFFER_SIZE>
   constexpr size_t size = DEVICE_INFO_BUFFER_SIZE;
   char *buf = buffer.data();
 
-  const LogString *flash_mode = FlashModeStrings::get_log_str(
-      static_cast<uint8_t>(ESP.getFlashChipMode()),  // NOLINT(readability-static-accessed-through-instance)
-      FlashModeStrings::LAST_INDEX);
+  const LogString *flash_mode;
+  switch (ESP.getFlashChipMode()) {  // NOLINT(readability-static-accessed-through-instance)
+    case FM_QIO:
+      flash_mode = LOG_STR("QIO");
+      break;
+    case FM_QOUT:
+      flash_mode = LOG_STR("QOUT");
+      break;
+    case FM_DIO:
+      flash_mode = LOG_STR("DIO");
+      break;
+    case FM_DOUT:
+      flash_mode = LOG_STR("DOUT");
+      break;
+    default:
+      flash_mode = LOG_STR("UNKNOWN");
+  }
   uint32_t flash_size = ESP.getFlashChipSize() / 1024;       // NOLINT(readability-static-accessed-through-instance)
   uint32_t flash_speed = ESP.getFlashChipSpeed() / 1000000;  // NOLINT(readability-static-accessed-through-instance)
   ESP_LOGD(TAG, "Flash Chip: Size=%" PRIu32 "kB Speed=%" PRIu32 "MHz Mode=%s", flash_size, flash_speed,

esphome/components/mqtt/mqtt_climate.cpp

@@ -300,9 +300,11 @@ const EntityBase *MQTTClimateComponent::get_entity() const { return this->device
 
 bool MQTTClimateComponent::publish_state_() {
   auto traits = this->device_->get_traits();
+  // Reusable stack buffer for topic construction (avoids heap allocation per publish)
+  char topic_buf[MQTT_DEFAULT_TOPIC_MAX_LEN];
   // mode
   bool success = true;
-  if (!this->publish(this->get_mode_state_topic(), climate_mode_to_mqtt_str(this->device_->mode)))
+  if (!this->publish(this->get_mode_state_topic_to(topic_buf), climate_mode_to_mqtt_str(this->device_->mode)))
     success = false;
   int8_t target_accuracy = traits.get_target_temperature_accuracy_decimals();
   int8_t current_accuracy = traits.get_current_temperature_accuracy_decimals();
@@ -311,68 +313,70 @@ bool MQTTClimateComponent::publish_state_() {
   if (traits.has_feature_flags(climate::CLIMATE_SUPPORTS_CURRENT_TEMPERATURE) &&
       !std::isnan(this->device_->current_temperature)) {
     len = value_accuracy_to_buf(payload, this->device_->current_temperature, current_accuracy);
-    if (!this->publish(this->get_current_temperature_state_topic(), payload, len))
+    if (!this->publish(this->get_current_temperature_state_topic_to(topic_buf), payload, len))
       success = false;
   }
   if (traits.has_feature_flags(climate::CLIMATE_SUPPORTS_TWO_POINT_TARGET_TEMPERATURE |
                                climate::CLIMATE_REQUIRES_TWO_POINT_TARGET_TEMPERATURE)) {
     len = value_accuracy_to_buf(payload, this->device_->target_temperature_low, target_accuracy);
-    if (!this->publish(this->get_target_temperature_low_state_topic(), payload, len))
+    if (!this->publish(this->get_target_temperature_low_state_topic_to(topic_buf), payload, len))
       success = false;
     len = value_accuracy_to_buf(payload, this->device_->target_temperature_high, target_accuracy);
-    if (!this->publish(this->get_target_temperature_high_state_topic(), payload, len))
+    if (!this->publish(this->get_target_temperature_high_state_topic_to(topic_buf), payload, len))
       success = false;
   } else {
     len = value_accuracy_to_buf(payload, this->device_->target_temperature, target_accuracy);
-    if (!this->publish(this->get_target_temperature_state_topic(), payload, len))
+    if (!this->publish(this->get_target_temperature_state_topic_to(topic_buf), payload, len))
       success = false;
   }
 
   if (traits.has_feature_flags(climate::CLIMATE_SUPPORTS_CURRENT_HUMIDITY) &&
       !std::isnan(this->device_->current_humidity)) {
     len = value_accuracy_to_buf(payload, this->device_->current_humidity, 0);
-    if (!this->publish(this->get_current_humidity_state_topic(), payload, len))
+    if (!this->publish(this->get_current_humidity_state_topic_to(topic_buf), payload, len))
       success = false;
   }
   if (traits.has_feature_flags(climate::CLIMATE_SUPPORTS_TARGET_HUMIDITY) &&
       !std::isnan(this->device_->target_humidity)) {
     len = value_accuracy_to_buf(payload, this->device_->target_humidity, 0);
-    if (!this->publish(this->get_target_humidity_state_topic(), payload, len))
+    if (!this->publish(this->get_target_humidity_state_topic_to(topic_buf), payload, len))
       success = false;
   }
 
   if (traits.get_supports_presets() || !traits.get_supported_custom_presets().empty()) {
     if (this->device_->has_custom_preset()) {
-      if (!this->publish(this->get_preset_state_topic(), this->device_->get_custom_preset()))
+      if (!this->publish(this->get_preset_state_topic_to(topic_buf), this->device_->get_custom_preset().c_str()))
         success = false;
     } else if (this->device_->preset.has_value()) {
-      if (!this->publish(this->get_preset_state_topic(), climate_preset_to_mqtt_str(this->device_->preset.value())))
+      if (!this->publish(this->get_preset_state_topic_to(topic_buf),
+                         climate_preset_to_mqtt_str(this->device_->preset.value())))
         success = false;
-    } else if (!this->publish(this->get_preset_state_topic(), "")) {
+    } else if (!this->publish(this->get_preset_state_topic_to(topic_buf), "")) {
       success = false;
     }
   }
 
   if (traits.has_feature_flags(climate::CLIMATE_SUPPORTS_ACTION)) {
-    if (!this->publish(this->get_action_state_topic(), climate_action_to_mqtt_str(this->device_->action)))
+    if (!this->publish(this->get_action_state_topic_to(topic_buf), climate_action_to_mqtt_str(this->device_->action)))
       success = false;
   }
 
   if (traits.get_supports_fan_modes()) {
     if (this->device_->has_custom_fan_mode()) {
-      if (!this->publish(this->get_fan_mode_state_topic(), this->device_->get_custom_fan_mode()))
+      if (!this->publish(this->get_fan_mode_state_topic_to(topic_buf), this->device_->get_custom_fan_mode().c_str()))
         success = false;
     } else if (this->device_->fan_mode.has_value()) {
-      if (!this->publish(this->get_fan_mode_state_topic(),
+      if (!this->publish(this->get_fan_mode_state_topic_to(topic_buf),
                          climate_fan_mode_to_mqtt_str(this->device_->fan_mode.value())))
         success = false;
-    } else if (!this->publish(this->get_fan_mode_state_topic(), "")) {
+    } else if (!this->publish(this->get_fan_mode_state_topic_to(topic_buf), "")) {
       success = false;
     }
   }
 
   if (traits.get_supports_swing_modes()) {
-    if (!this->publish(this->get_swing_mode_state_topic(), climate_swing_mode_to_mqtt_str(this->device_->swing_mode)))
+    if (!this->publish(this->get_swing_mode_state_topic_to(topic_buf),
+                       climate_swing_mode_to_mqtt_str(this->device_->swing_mode)))
       success = false;
   }
 

esphome/components/mqtt/mqtt_component.h

@@ -55,6 +55,11 @@ void log_mqtt_component(const char *tag, MQTTComponent *obj, bool state_topic, b
 \
  public: \
   void set_custom_##name##_##type##_topic(const std::string &topic) { this->custom_##name##_##type##_topic_ = topic; } \
+  StringRef get_##name##_##type##_topic_to(std::span<char, MQTT_DEFAULT_TOPIC_MAX_LEN> buf) const { \
+    if (!this->custom_##name##_##type##_topic_.empty()) \
+      return StringRef(this->custom_##name##_##type##_topic_.data(), this->custom_##name##_##type##_topic_.size()); \
+    return this->get_default_topic_for_to_(buf, #name "/" #type, sizeof(#name "/" #type) - 1); \
+  } \
   std::string get_##name##_##type##_topic() const { \
     if (this->custom_##name##_##type##_topic_.empty()) \
       return this->get_default_topic_for_(#name "/" #type); \

esphome/components/mqtt/mqtt_cover.cpp

@@ -112,19 +112,19 @@ bool MQTTCoverComponent::send_initial_state() { return this->publish_state(); }
 bool MQTTCoverComponent::publish_state() {
   auto traits = this->cover_->get_traits();
   bool success = true;
+  char topic_buf[MQTT_DEFAULT_TOPIC_MAX_LEN];
   if (traits.get_supports_position()) {
     char pos[VALUE_ACCURACY_MAX_LEN];
     size_t len = value_accuracy_to_buf(pos, roundf(this->cover_->position * 100), 0);
-    if (!this->publish(this->get_position_state_topic(), pos, len))
+    if (!this->publish(this->get_position_state_topic_to(topic_buf), pos, len))
       success = false;
   }
   if (traits.get_supports_tilt()) {
     char pos[VALUE_ACCURACY_MAX_LEN];
     size_t len = value_accuracy_to_buf(pos, roundf(this->cover_->tilt * 100), 0);
-    if (!this->publish(this->get_tilt_state_topic(), pos, len))
+    if (!this->publish(this->get_tilt_state_topic_to(topic_buf), pos, len))
       success = false;
   }
-  char topic_buf[MQTT_DEFAULT_TOPIC_MAX_LEN];
   if (!this->publish(this->get_state_topic_to_(topic_buf),
                      cover_state_to_mqtt_str(this->cover_->current_operation, this->cover_->position,
                                              traits.get_supports_position())))

esphome/components/mqtt/mqtt_fan.cpp

@@ -173,19 +173,20 @@ bool MQTTFanComponent::publish_state() {
   this->publish(this->get_state_topic_to_(topic_buf), state_s);
   bool failed = false;
   if (this->state_->get_traits().supports_direction()) {
-    bool success = this->publish(this->get_direction_state_topic(), fan_direction_to_mqtt_str(this->state_->direction));
+    bool success = this->publish(this->get_direction_state_topic_to(topic_buf),
+                                 fan_direction_to_mqtt_str(this->state_->direction));
     failed = failed || !success;
   }
   if (this->state_->get_traits().supports_oscillation()) {
-    bool success =
-        this->publish(this->get_oscillation_state_topic(), fan_oscillation_to_mqtt_str(this->state_->oscillating));
+    bool success = this->publish(this->get_oscillation_state_topic_to(topic_buf),
+                                 fan_oscillation_to_mqtt_str(this->state_->oscillating));
     failed = failed || !success;
   }
   auto traits = this->state_->get_traits();
   if (traits.supports_speed()) {
     char buf[12];
     size_t len = buf_append_printf(buf, sizeof(buf), 0, "%d", this->state_->speed);
-    bool success = this->publish(this->get_speed_level_state_topic(), buf, len);
+    bool success = this->publish(this->get_speed_level_state_topic_to(topic_buf), buf, len);
     failed = failed || !success;
   }
   return !failed;

esphome/components/mqtt/mqtt_valve.cpp

@@ -87,13 +87,13 @@ bool MQTTValveComponent::send_initial_state() { return this->publish_state(); }
 bool MQTTValveComponent::publish_state() {
   auto traits = this->valve_->get_traits();
   bool success = true;
+  char topic_buf[MQTT_DEFAULT_TOPIC_MAX_LEN];
   if (traits.get_supports_position()) {
     char pos[VALUE_ACCURACY_MAX_LEN];
     size_t len = value_accuracy_to_buf(pos, roundf(this->valve_->position * 100), 0);
-    if (!this->publish(this->get_position_state_topic(), pos, len))
+    if (!this->publish(this->get_position_state_topic_to(topic_buf), pos, len))
       success = false;
   }
-  char topic_buf[MQTT_DEFAULT_TOPIC_MAX_LEN];
   if (!this->publish(this->get_state_topic_to_(topic_buf),
                      valve_state_to_mqtt_str(this->valve_->current_operation, this->valve_->position,
                                              traits.get_supports_position())))