[api] State the destructor trade-off as a codebase rule, not a language guarantee

A generated decodable message that lost its decode() would now fail to compile instead of
silently keeping its defaults. The asserts cover exactly the classes that derive from
ProtoDecodableMessage, under one ifdef per run instead of one per line, and the generator
tests pin the inline decode() wrapper, its absence on fixed vector messages, and the
this-> free static body.

esphome/components/api/api_pb2.h

@@ -419,12 +419,15 @@ class HelloRequest final : public ProtoDecodableMessage {
   StringRef client_info{};
   uint32_t api_version_major{0};
   uint32_t api_version_minor{0};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class HelloResponse final : public ProtoMessage {
  public:
@@ -457,6 +460,9 @@ class DisconnectRequest final : public ProtoDecodableMessage {
   const LogString *message_name() const override { return LOG_STR("disconnect_request"); }
 #endif
   enums::DisconnectReason reason{};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
     return encode_msg(this, buffer PROTO_ENCODE_DEBUG_ARG);
@@ -468,7 +474,7 @@ class DisconnectRequest final : public ProtoDecodableMessage {
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class DisconnectResponse final : public ProtoMessage {
  public:
@@ -839,12 +845,15 @@ class CoverCommandRequest final : public CommandProtoMessage {
   bool has_tilt{false};
   float tilt{0.0f};
   bool stop{false};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 #endif
 #ifdef USE_FAN
@@ -913,12 +922,15 @@ class FanCommandRequest final : public CommandProtoMessage {
   int32_t speed_level{0};
   bool has_preset_mode{false};
   StringRef preset_mode{};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 #endif
 #ifdef USE_LIGHT
@@ -1009,12 +1021,15 @@ class LightCommandRequest final : public CommandProtoMessage {
   uint32_t flash_length{0};
   bool has_effect{false};
   StringRef effect{};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 #endif
 #ifdef USE_SENSOR
@@ -1114,12 +1129,15 @@ class SwitchCommandRequest final : public CommandProtoMessage {
   const LogString *message_name() const override { return LOG_STR("switch_command_request"); }
 #endif
   bool state{false};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 #endif
 #ifdef USE_TEXT_SENSOR
@@ -1174,12 +1192,15 @@ class SubscribeLogsRequest final : public ProtoDecodableMessage {
 #endif
   enums::LogLevel level{};
   bool dump_config{false};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class SubscribeLogsResponse final : public ProtoMessage {
  public:
@@ -1217,12 +1238,15 @@ class NoiseEncryptionSetKeyRequest final : public ProtoDecodableMessage {
 #endif
   const uint8_t *key{nullptr};
   uint16_t key_len{0};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class NoiseEncryptionSetKeyResponse final : public ProtoMessage {
  public:
@@ -1311,12 +1335,15 @@ class HomeassistantActionResponse final : public ProtoDecodableMessage {
   const uint8_t *response_data{nullptr};
   uint16_t response_data_len{0};
 #endif
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 #endif
 #ifdef USE_API_HOMEASSISTANT_STATES
@@ -1352,12 +1379,15 @@ class HomeAssistantStateResponse final : public ProtoDecodableMessage {
   StringRef entity_id{};
   StringRef state{};
   StringRef attribute{};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 #endif
 class GetTimeRequest final : public ProtoMessage {
@@ -1381,12 +1411,15 @@ class DSTRule final : public ProtoDecodableMessage {
   uint32_t month{0};
   uint32_t week{0};
   uint32_t day_of_week{0};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class ParsedTimezone final : public ProtoDecodableMessage {
  public:
@@ -1394,12 +1427,15 @@ class ParsedTimezone final : public ProtoDecodableMessage {
   int32_t dst_offset_seconds{0};
   DSTRule dst_start{};
   DSTRule dst_end{};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class GetTimeResponse final : public ProtoDecodableMessage {
  public:
@@ -1411,12 +1447,15 @@ class GetTimeResponse final : public ProtoDecodableMessage {
   uint32_t epoch_seconds{0};
   ParsedTimezone parsed_timezone{};
   bool has_parsed_timezone{false};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 #ifdef USE_API_USER_DEFINED_ACTIONS
 class ListEntitiesServicesArgument final : public ProtoMessage {
@@ -1484,7 +1523,7 @@ class ExecuteServiceArgument final : public ProtoDecodableMessage {
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class ExecuteServiceRequest final : public ProtoDecodableMessage {
  public:
@@ -1507,7 +1546,7 @@ class ExecuteServiceRequest final : public ProtoDecodableMessage {
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 #endif
 #ifdef USE_API_USER_DEFINED_ACTION_RESPONSES
@@ -1593,12 +1632,15 @@ class CameraImageRequest final : public ProtoDecodableMessage {
 #endif
   bool single{false};
   bool stream{false};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 #endif
 #ifdef USE_CLIMATE
@@ -1699,12 +1741,15 @@ class ClimateCommandRequest final : public CommandProtoMessage {
   StringRef custom_preset{};
   bool has_target_humidity{false};
   float target_humidity{0.0f};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 #endif
 #ifdef USE_WATER_HEATER
@@ -1771,12 +1816,15 @@ class WaterHeaterCommandRequest final : public CommandProtoMessage {
   uint32_t state{0};
   float target_temperature_low{0.0f};
   float target_temperature_high{0.0f};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 #endif
 #ifdef USE_NUMBER
@@ -1834,12 +1882,15 @@ class NumberCommandRequest final : public CommandProtoMessage {
   const LogString *message_name() const override { return LOG_STR("number_command_request"); }
 #endif
   float state{0.0f};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 #endif
 #ifdef USE_SELECT
@@ -1892,12 +1943,15 @@ class SelectCommandRequest final : public CommandProtoMessage {
   const LogString *message_name() const override { return LOG_STR("select_command_request"); }
 #endif
   StringRef state{};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 #endif
 #ifdef USE_SIREN
@@ -1958,12 +2012,15 @@ class SirenCommandRequest final : public CommandProtoMessage {
   uint32_t duration{0};
   bool has_volume{false};
   float volume{0.0f};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 #endif
 #ifdef USE_LOCK
@@ -2020,12 +2077,15 @@ class LockCommandRequest final : public CommandProtoMessage {
   enums::LockCommand command{};
   bool has_code{false};
   StringRef code{};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 #endif
 #ifdef USE_BUTTON
@@ -2056,12 +2116,15 @@ class ButtonCommandRequest final : public CommandProtoMessage {
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const LogString *message_name() const override { return LOG_STR("button_command_request"); }
 #endif
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 #endif
 #ifdef USE_MEDIA_PLAYER
@@ -2142,12 +2205,15 @@ class MediaPlayerCommandRequest final : public CommandProtoMessage {
   StringRef media_url{};
   bool has_announcement{false};
   bool announcement{false};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 #endif
 #ifdef USE_BLUETOOTH_PROXY
@@ -2159,12 +2225,15 @@ class SubscribeBluetoothLEAdvertisementsRequest final : public ProtoDecodableMes
   const LogString *message_name() const override { return LOG_STR("subscribe_bluetooth_le_advertisements_request"); }
 #endif
   uint32_t flags{0};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class BluetoothLERawAdvertisement final : public ProtoMessage {
  public:
@@ -2213,12 +2282,15 @@ class BluetoothDeviceRequest final : public ProtoDecodableMessage {
   enums::BluetoothDeviceRequestType request_type{};
   bool has_address_type{false};
   uint32_t address_type{0};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class BluetoothDeviceConnectionResponse final : public ProtoMessage {
  public:
@@ -2251,12 +2323,15 @@ class BluetoothGATTGetServicesRequest final : public ProtoDecodableMessage {
   const LogString *message_name() const override { return LOG_STR("bluetooth_gatt_get_services_request"); }
 #endif
   uint64_t address{0};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class BluetoothGATTDescriptor final : public ProtoMessage {
  public:
@@ -2362,12 +2437,15 @@ class BluetoothGATTReadRequest final : public ProtoDecodableMessage {
 #endif
   uint64_t address{0};
   uint32_t handle{0};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class BluetoothGATTReadResponse final : public ProtoMessage {
  public:
@@ -2408,12 +2486,15 @@ class BluetoothGATTWriteRequest final : public ProtoDecodableMessage {
   bool response{false};
   const uint8_t *data{nullptr};
   uint16_t data_len{0};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class BluetoothGATTReadDescriptorRequest final : public ProtoDecodableMessage {
  public:
@@ -2424,12 +2505,15 @@ class BluetoothGATTReadDescriptorRequest final : public ProtoDecodableMessage {
 #endif
   uint64_t address{0};
   uint32_t handle{0};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class BluetoothGATTWriteDescriptorRequest final : public ProtoDecodableMessage {
  public:
@@ -2442,12 +2526,15 @@ class BluetoothGATTWriteDescriptorRequest final : public ProtoDecodableMessage {
   uint32_t handle{0};
   const uint8_t *data{nullptr};
   uint16_t data_len{0};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class BluetoothGATTNotifyRequest final : public ProtoDecodableMessage {
  public:
@@ -2459,12 +2546,15 @@ class BluetoothGATTNotifyRequest final : public ProtoDecodableMessage {
   uint64_t address{0};
   uint32_t handle{0};
   bool enable{false};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class BluetoothGATTNotifyDataResponse final : public ProtoMessage {
  public:
@@ -2677,12 +2767,15 @@ class BluetoothScannerSetModeRequest final : public ProtoDecodableMessage {
   const LogString *message_name() const override { return LOG_STR("bluetooth_scanner_set_mode_request"); }
 #endif
   enums::BluetoothScannerMode mode{};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 #endif
 #ifdef USE_VOICE_ASSISTANT
@@ -2695,12 +2788,15 @@ class SubscribeVoiceAssistantRequest final : public ProtoDecodableMessage {
 #endif
   bool subscribe{false};
   uint32_t flags{0};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class VoiceAssistantAudioSettings final : public ProtoMessage {
  public:
@@ -2752,23 +2848,29 @@ class VoiceAssistantResponse final : public ProtoDecodableMessage {
 #endif
   uint32_t port{0};
   bool error{false};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class VoiceAssistantEventData final : public ProtoDecodableMessage {
  public:
   StringRef name{};
   StringRef value{};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class VoiceAssistantEventResponse final : public ProtoDecodableMessage {
  public:
@@ -2779,12 +2881,15 @@ class VoiceAssistantEventResponse final : public ProtoDecodableMessage {
 #endif
   enums::VoiceAssistantEvent event_type{};
   std::vector<VoiceAssistantEventData> data{};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class VoiceAssistantAudio final : public ProtoDecodableMessage {
  public:
@@ -2798,6 +2903,9 @@ class VoiceAssistantAudio final : public ProtoDecodableMessage {
   bool end{false};
   const uint8_t *data2{nullptr};
   uint16_t data2_len{0};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
     return encode_msg(this, buffer PROTO_ENCODE_DEBUG_ARG);
@@ -2809,7 +2917,7 @@ class VoiceAssistantAudio final : public ProtoDecodableMessage {
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class VoiceAssistantTimerEventResponse final : public ProtoDecodableMessage {
  public:
@@ -2824,12 +2932,15 @@ class VoiceAssistantTimerEventResponse final : public ProtoDecodableMessage {
   uint32_t total_seconds{0};
   uint32_t seconds_left{0};
   bool is_active{false};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class VoiceAssistantAnnounceRequest final : public ProtoDecodableMessage {
  public:
@@ -2842,12 +2953,15 @@ class VoiceAssistantAnnounceRequest final : public ProtoDecodableMessage {
   StringRef text{};
   StringRef preannounce_media_id{};
   bool start_conversation{false};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class VoiceAssistantAnnounceFinished final : public ProtoMessage {
  public:
@@ -2895,12 +3009,15 @@ class VoiceAssistantExternalWakeWord final : public ProtoDecodableMessage {
   uint32_t model_size{0};
   StringRef model_hash{};
   StringRef url{};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class VoiceAssistantConfigurationRequest final : public ProtoDecodableMessage {
  public:
@@ -2910,12 +3027,15 @@ class VoiceAssistantConfigurationRequest final : public ProtoDecodableMessage {
   const LogString *message_name() const override { return LOG_STR("voice_assistant_configuration_request"); }
 #endif
   std::vector<VoiceAssistantExternalWakeWord> external_wake_words{};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class VoiceAssistantConfigurationResponse final : public ProtoMessage {
  public:
@@ -2947,12 +3067,15 @@ class VoiceAssistantSetConfiguration final : public ProtoDecodableMessage {
   const LogString *message_name() const override { return LOG_STR("voice_assistant_set_configuration"); }
 #endif
   std::vector<std::string> active_wake_words{};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 #endif
 #ifdef USE_ALARM_CONTROL_PANEL
@@ -3007,12 +3130,15 @@ class AlarmControlPanelCommandRequest final : public CommandProtoMessage {
 #endif
   enums::AlarmControlPanelStateCommand command{};
   StringRef code{};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 #endif
 #ifdef USE_TEXT
@@ -3068,12 +3194,15 @@ class TextCommandRequest final : public CommandProtoMessage {
   const LogString *message_name() const override { return LOG_STR("text_command_request"); }
 #endif
   StringRef state{};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 #endif
 #ifdef USE_DATETIME_DATE
@@ -3129,12 +3258,15 @@ class DateCommandRequest final : public CommandProtoMessage {
   uint32_t year{0};
   uint32_t month{0};
   uint32_t day{0};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 #endif
 #ifdef USE_DATETIME_TIME
@@ -3190,12 +3322,15 @@ class TimeCommandRequest final : public CommandProtoMessage {
   uint32_t hour{0};
   uint32_t minute{0};
   uint32_t second{0};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 #endif
 #ifdef USE_EVENT
@@ -3296,12 +3431,15 @@ class ValveCommandRequest final : public CommandProtoMessage {
   bool has_position{false};
   float position{0.0f};
   bool stop{false};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 #endif
 #ifdef USE_DATETIME_DATETIME
@@ -3353,12 +3491,15 @@ class DateTimeCommandRequest final : public CommandProtoMessage {
   const LogString *message_name() const override { return LOG_STR("date_time_command_request"); }
 #endif
   uint32_t epoch_seconds{0};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 #endif
 #ifdef USE_UPDATE
@@ -3418,12 +3559,15 @@ class UpdateCommandRequest final : public CommandProtoMessage {
   const LogString *message_name() const override { return LOG_STR("update_command_request"); }
 #endif
   enums::UpdateCommand command{};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 #endif
 #ifdef USE_ZWAVE_PROXY
@@ -3436,6 +3580,9 @@ class ZWaveProxyFrame final : public ProtoDecodableMessage {
 #endif
   const uint8_t *data{nullptr};
   uint16_t data_len{0};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
     return encode_msg(this, buffer PROTO_ENCODE_DEBUG_ARG);
@@ -3447,7 +3594,7 @@ class ZWaveProxyFrame final : public ProtoDecodableMessage {
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class ZWaveProxyRequest final : public ProtoDecodableMessage {
  public:
@@ -3459,6 +3606,9 @@ class ZWaveProxyRequest final : public ProtoDecodableMessage {
   enums::ZWaveProxyRequestType type{};
   const uint8_t *data{nullptr};
   uint16_t data_len{0};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
   static uint8_t *encode_msg(const void *self, ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM);
   uint8_t *encode(ProtoWriteBuffer &buffer PROTO_ENCODE_DEBUG_PARAM) const {
     return encode_msg(this, buffer PROTO_ENCODE_DEBUG_ARG);
@@ -3470,7 +3620,7 @@ class ZWaveProxyRequest final : public ProtoDecodableMessage {
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class ZWaveProxyRequestResponse final : public ProtoMessage {
  public:
@@ -3535,12 +3685,15 @@ class InfraredRFTransmitRawTimingsRequest final : public ProtoDecodableMessage {
   uint16_t timings_length_{0};
   uint16_t timings_count_{0};
   uint32_t modulation{0};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class InfraredRFReceiveEvent final : public ProtoMessage {
  public:
@@ -3606,12 +3759,15 @@ class SerialProxyConfigureRequest final : public ProtoDecodableMessage {
   enums::SerialProxyParity parity{};
   uint32_t stop_bits{0};
   uint32_t data_size{0};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class SerialProxyDataReceived final : public ProtoMessage {
  public:
@@ -3649,12 +3805,15 @@ class SerialProxyWriteRequest final : public ProtoDecodableMessage {
   uint32_t instance{0};
   const uint8_t *data{nullptr};
   uint16_t data_len{0};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class SerialProxySetModemPinsRequest final : public ProtoDecodableMessage {
  public:
@@ -3665,12 +3824,15 @@ class SerialProxySetModemPinsRequest final : public ProtoDecodableMessage {
 #endif
   uint32_t instance{0};
   uint32_t line_states{0};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class SerialProxyGetModemPinsRequest final : public ProtoDecodableMessage {
  public:
@@ -3680,12 +3842,15 @@ class SerialProxyGetModemPinsRequest final : public ProtoDecodableMessage {
   const LogString *message_name() const override { return LOG_STR("serial_proxy_get_modem_pins_request"); }
 #endif
   uint32_t instance{0};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class SerialProxyGetModemPinsResponse final : public ProtoMessage {
  public:
@@ -3718,12 +3883,15 @@ class SerialProxyRequest final : public ProtoDecodableMessage {
 #endif
   uint32_t instance{0};
   enums::SerialProxyRequestType type{};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class SerialProxyRequestResponse final : public ProtoMessage {
  public:
@@ -3762,12 +3930,15 @@ class BluetoothSetConnectionParamsRequest final : public ProtoDecodableMessage {
   uint32_t max_interval{0};
   uint32_t latency{0};
   uint32_t timeout{0};
+  void decode(const uint8_t *buffer, size_t length) {
+    ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);
+  }
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif
 
  protected:
-  void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;
+  static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
 };
 class BluetoothSetConnectionParamsResponse final : public ProtoMessage {
  public:

esphome/components/api/proto.cpp

@@ -210,7 +210,7 @@ void ProtoWriteBuffer::debug_check_encode_size_(uint32_t field_id, uint32_t expe
 
 #endif
 
-void ProtoDecodableMessage::decode(const uint8_t *buffer, size_t length) {
+void ProtoDecodableMessage::decode_fields(void *msg, const uint8_t *buffer, size_t length, DecodeFieldFn field) {
   const uint8_t *ptr = buffer;
   const uint8_t *end = buffer + length;
 
@@ -281,7 +281,7 @@ void ProtoDecodableMessage::decode(const uint8_t *buffer, size_t length) {
           return;
       }
     }
-    this->decode_field(tag, data, scalar);
+    field(msg, tag, data, scalar);
   }
 }
 

esphome/components/api/proto.h

@@ -10,6 +10,7 @@
 
 #include <cassert>
 #include <cstring>
+#include <type_traits>
 #include <vector>
 
 #ifdef ESPHOME_LOG_HAS_VERY_VERBOSE
@@ -720,7 +721,13 @@ class ProtoMessage {
 // Base class for messages that support decoding
 class ProtoDecodableMessage : public ProtoMessage {
  public:
-  void decode(const uint8_t *buffer, size_t length);
+  /// Stores one decoded field into \p msg; generated per message type. \p scalar is the varint or
+  /// fixed32 value, or the length of the length-delimited payload at \p data. An unknown field or
+  /// wrong wire type matches no case and is skipped.
+  using DecodeFieldFn = void (*)(void *msg, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);
+  /// Walk \p buffer and hand every field to \p field. The generated decode() passes the message's
+  /// own decode_field, so decodable messages carry no vtable.
+  static void decode_fields(void *msg, const uint8_t *buffer, size_t length, DecodeFieldFn field);
 
   /**
    * Count occurrences of a repeated field in a protobuf buffer.
@@ -732,14 +739,15 @@ class ProtoDecodableMessage : public ProtoMessage {
    * @return Number of times the field appears in the buffer
    */
   static uint32_t count_repeated_field(const uint8_t *buffer, size_t length, uint32_t target_field_id);
-
+  // The destructor stays accessible on purpose: the generated messages are aggregates that brace
- protected:
+  // initialise sub message members, which copies a base temporary. That trades away the compile time
-  ~ProtoDecodableMessage() = default;
+  // guard against deleting through this type; messages are stack locals and never owned through a base
-  /// Store one decoded field; \p scalar is the varint or fixed32 value, or the length of the
+  // pointer. ProtoMessage keeps its guard for the dump builds.
-  /// length-delimited payload at \p data. An unknown field or wrong wire type matches no case and is skipped.
-  /// Three register arguments keep the decode loop free of spills.
-  virtual void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) {}
 };
+#ifndef HAS_PROTO_MESSAGE_DUMP
+// decode() passes decode_field explicitly, so nothing here may add a vtable
+static_assert(!std::is_polymorphic_v<ProtoDecodableMessage>, "decodable messages carry no vtable");
+#endif
 
 class ProtoSize {
  public:

script/api_protobuf/api_protobuf.py

@@ -2536,8 +2536,8 @@ def build_message_type(
 
     # Get source direction to determine if we need decode/encode methods
     source = message_source_map[desc.name]
-    needs_decode = source in (SOURCE_BOTH, SOURCE_CLIENT)
+    needs_decode = message_needs_decode(source)
-    needs_encode = source in (SOURCE_BOTH, SOURCE_SERVER)
+    needs_encode = message_needs_encode(source)
 
     # Add MESSAGE_TYPE method if this is a service message
     if message_id is not None:
@@ -2661,15 +2661,22 @@ def build_message_type(
 
     cpp = ""
     if decode:
-        o = f"void {desc.name}::decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) {{\n"
+        o = f"void {desc.name}::decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) {{\n"
+        o += f"  auto &msg = *static_cast<{desc.name} *>(self);\n"
         o += "  const ProtoFieldValue value(data, scalar);\n"
         o += "  switch (tag) {\n"
-        o += indent("\n".join(decode), "    ") + "\n"
+        o += indent("\n".join(decode), "    ").replace("this->", "msg.") + "\n"
         o += "  }\n"
         o += "}\n"
         cpp += o
-        prot = "void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;"
+        prot = "static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);"
         protected_content.insert(0, prot)
+        if not fixed_vector_fields:
+            public_content.append(
+                "void decode(const uint8_t *buffer, size_t length) {\n"
+                "  ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);\n"
+                "}"
+            )
 
     # Generate custom decode() override for messages with FixedVector fields
     if fixed_vector_fields:
@@ -2679,8 +2686,8 @@ def build_message_type(
         for field_name, field_number in fixed_vector_fields:
             o += f"  uint32_t count_{field_name} = ProtoDecodableMessage::count_repeated_field(buffer, length, {field_number});\n"
             o += f"  this->{field_name}.init(count_{field_name});\n"
-        # Call parent decode to populate the fields
+        # Then the shared loop fills them
-        o += "  ProtoDecodableMessage::decode(buffer, length);\n"
+        o += "  ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);\n"
         o += "}\n"
         cpp += o
         # Generate the decode() declaration in header (public method)
@@ -2839,6 +2846,23 @@ def get_field_opt(
     return field.options.Extensions[opt]
 
 
+def message_needs_decode(source: int) -> bool:
+    return source in (SOURCE_BOTH, SOURCE_CLIENT)
+
+
+def message_needs_encode(source: int) -> bool:
+    return source in (SOURCE_BOTH, SOURCE_SERVER)
+
+
+def is_decodable_class(desc: descriptor.DescriptorProto, source: int) -> bool:
+    """Whether the generated class derives from ProtoDecodableMessage: decoded, and either on a
+    decodable base class or with at least one live field."""
+    return message_needs_decode(source) and (
+        get_base_class(desc) is not None
+        or any(not field.options.deprecated for field in desc.field)
+    )
+
+
 def get_base_class(desc: descriptor.DescriptorProto) -> str | None:
     """Get the base_class option from a message descriptor."""
     if not desc.options.HasExtension(pb.base_class):
@@ -2940,11 +2964,11 @@ def build_base_class(
 
     # Determine if any message using this base class needs decoding/encoding
     needs_decode = any(
-        message_source_map.get(msg.name, SOURCE_BOTH) in (SOURCE_BOTH, SOURCE_CLIENT)
+        message_needs_decode(message_source_map.get(msg.name, SOURCE_BOTH))
         for msg in messages
     )
     needs_encode = any(
-        message_source_map.get(msg.name, SOURCE_BOTH) in (SOURCE_BOTH, SOURCE_SERVER)
+        message_needs_encode(message_source_map.get(msg.name, SOURCE_BOTH))
         for msg in messages
     )
 
@@ -3378,6 +3402,7 @@ static void dump_bytes_field(DumpBuffer &out, const char *field_name, const uint
 
     # Generate message types with base class information
     # Simple grouping by ifdef
+    decodable_messages: list[tuple[str, str | None]] = []
     current_ifdef = None
 
     for m in mt:
@@ -3394,6 +3419,8 @@ static void dump_bytes_field(DumpBuffer &out, const char *field_name, const uint
             continue
 
         s, c, dc = build_message_type(m, base_class_fields, message_source_map)
+        if is_decodable_class(m, message_source_map[m.name]):
+            decodable_messages.append((m.name, message_ifdef_map.get(m.name)))
         msg_ifdef = message_ifdef_map.get(m.name)
 
         # Handle ifdef changes
@@ -3420,6 +3447,22 @@ static void dump_bytes_field(DumpBuffer &out, const char *field_name, const uint
         cpp += "#endif\n"
         dump_cpp += "#endif\n"
 
+    # decode() passes decode_field explicitly, so without the dump virtuals no decodable message
+    # may carry a vtable; a build at any level below VERY_VERBOSE proves it
+    cpp += "#ifndef HAS_PROTO_MESSAGE_DUMP\n"
+    assert_ifdef = None
+    for name, msg_ifdef in decodable_messages:
+        if msg_ifdef != assert_ifdef:
+            if assert_ifdef is not None:
+                cpp += "#endif\n"
+            if msg_ifdef is not None:
+                cpp += _make_ifdef_line(msg_ifdef) + "\n"
+            assert_ifdef = msg_ifdef
+        cpp += f'static_assert(!std::is_polymorphic_v<{name}>, "decodable messages carry no vtable");\n'
+    if assert_ifdef is not None:
+        cpp += "#endif\n"
+    cpp += "#endif\n"
+
     content += """\
 
 }  // namespace esphome::api

tests/unit_tests/components/api/test_api_protobuf_generator.py

@@ -285,18 +285,19 @@ def test_a_fixed64_field_fails_at_generation_time() -> None:
         build_message_type(desc, {}, {"Wide": SOURCE_CLIENT})
 
 
-def test_message_gets_a_single_decode_field_override() -> None:
+def test_message_decodes_through_one_static_decode_field() -> None:
-    """All wire types of a decoded message land in one decode_field() switch."""
+    """All wire types of a decoded message land in one static decode_field() switch that the
+    inline decode() hands to the shared loop."""
     desc = descriptor_pb2.DescriptorProto(name="Mixed")
     desc.field.add(name="name", number=1, type=STRING)
     desc.field.add(name="count", number=2, type=UINT32)
     desc.field.add(name="level", number=3, type=FLOAT)
     header, cpp, _ = build_message_type(desc, {}, {"Mixed": SOURCE_CLIENT})
-    decl = "void decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) override;"
+    decl = "static void decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar);"
     assert header.count(decl) == 1
     assert (
         cpp.count(
-            "void Mixed::decode_field(uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) {"
+            "void Mixed::decode_field(void *self, uint32_t tag, const uint8_t *data, proto_varint_value_t scalar) {"
         )
         == 1
     )
@@ -308,3 +309,34 @@ def test_message_gets_a_single_decode_field_override() -> None:
         (3, "WIRE_TYPE_FIXED32"),
     ):
         assert f"case proto_tag({number}, {wire_type}):" in cpp, cpp
+    # The static body works on the cast message, never on this
+    assert "auto &msg = *static_cast<Mixed *>(self);" in cpp
+    assert "this->" not in cpp
+    assert (
+        header.count(
+            "ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);"
+        )
+        == 1
+    )
+
+
+def test_fixed_vector_message_keeps_its_own_decode() -> None:
+    """A message that sizes a FixedVector first decodes through its own decode(), not the inline one."""
+    desc = descriptor_pb2.DescriptorProto(name="Sized")
+    field = desc.field.add(name="values", number=1, type=UINT32)
+    field.label = descriptor_pb2.FieldDescriptorProto.LABEL_REPEATED
+    field.options.Extensions[pb.fixed_vector] = True
+    header, cpp, _ = build_message_type(desc, {}, {"Sized": SOURCE_CLIENT})
+    assert (
+        "ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);"
+        not in header
+    )
+    assert header.count("void decode(const uint8_t *buffer, size_t length);") == 1
+    assert "void Sized::decode(const uint8_t *buffer, size_t length) {" in cpp
+    assert "ProtoDecodableMessage::count_repeated_field(buffer, length, 1)" in cpp
+    assert (
+        cpp.count(
+            "ProtoDecodableMessage::decode_fields(this, buffer, length, &decode_field);"
+        )
+        == 1
+    )