Reduce memory required for sensor entities (#9201)

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

esphome/components/sensor/sensor.cpp

@@ -23,16 +23,22 @@ std::string state_class_to_string(StateClass state_class) {
 Sensor::Sensor() : state(NAN), raw_state(NAN) {}
 
 int8_t Sensor::get_accuracy_decimals() {
-  if (this->accuracy_decimals_.has_value())
-    return *this->accuracy_decimals_;
+  if (this->sensor_flags_.has_accuracy_override)
+    return this->accuracy_decimals_;
   return 0;
 }
-void Sensor::set_accuracy_decimals(int8_t accuracy_decimals) { this->accuracy_decimals_ = accuracy_decimals; }
+void Sensor::set_accuracy_decimals(int8_t accuracy_decimals) {
+  this->accuracy_decimals_ = accuracy_decimals;
+  this->sensor_flags_.has_accuracy_override = true;
+}
 
-void Sensor::set_state_class(StateClass state_class) { this->state_class_ = state_class; }
+void Sensor::set_state_class(StateClass state_class) {
+  this->state_class_ = state_class;
+  this->sensor_flags_.has_state_class_override = true;
+}
 StateClass Sensor::get_state_class() {
-  if (this->state_class_.has_value())
-    return *this->state_class_;
+  if (this->sensor_flags_.has_state_class_override)
+    return this->state_class_;
   return StateClass::STATE_CLASS_NONE;
 }
 

esphome/components/sensor/sensor.h

@@ -80,9 +80,9 @@ class Sensor : public EntityBase, public EntityBase_DeviceClass, public EntityBa
    * state changes to the database when they are published, even if the state is the
    * same as before.
    */
-  bool get_force_update() const { return force_update_; }
+  bool get_force_update() const { return sensor_flags_.force_update; }
   /// Set force update mode.
-  void set_force_update(bool force_update) { force_update_ = force_update; }
+  void set_force_update(bool force_update) { sensor_flags_.force_update = force_update; }
 
   /// Add a filter to the filter chain. Will be appended to the back.
   void add_filter(Filter *filter);
@@ -155,9 +155,17 @@ class Sensor : public EntityBase, public EntityBase_DeviceClass, public EntityBa
 
   Filter *filter_list_{nullptr};  ///< Store all active filters.
 
-  optional<int8_t> accuracy_decimals_;                  ///< Accuracy in decimals override
-  optional<StateClass> state_class_{STATE_CLASS_NONE};  ///< State class override
-  bool force_update_{false};                            ///< Force update mode
+  // Group small members together to avoid padding
+  int8_t accuracy_decimals_{-1};              ///< Accuracy in decimals (-1 = not set)
+  StateClass state_class_{STATE_CLASS_NONE};  ///< State class (STATE_CLASS_NONE = not set)
+
+  // Bit-packed flags for sensor-specific settings
+  struct SensorFlags {
+    uint8_t has_accuracy_override : 1;
+    uint8_t has_state_class_override : 1;
+    uint8_t force_update : 1;
+    uint8_t reserved : 5;  // Reserved for future use
+  } sensor_flags_{};
 };
 
 }  // namespace sensor

tests/integration/fixtures/host_mode_with_sensor.yaml

@@ -8,5 +8,8 @@ sensor:
     name: Test Sensor
     id: test_sensor
     unit_of_measurement: °C
+    accuracy_decimals: 2
+    state_class: measurement
+    force_update: true
     lambda: return 42.0;
     update_interval: 0.1s

tests/integration/test_host_mode_sensor.py

@@ -4,6 +4,7 @@ from __future__ import annotations
 
 import asyncio
 
+import aioesphomeapi
 from aioesphomeapi import EntityState
 import pytest
 
@@ -47,3 +48,23 @@ async def test_host_mode_with_sensor(
         # Verify the sensor state
         assert test_sensor_state.state == 42.0
         assert len(states) > 0, "No states received"
+
+        # Verify the optimized fields are working correctly
+        # Get entity info to check accuracy_decimals, state_class, etc.
+        entities, _ = await client.list_entities_services()
+        sensor_info: aioesphomeapi.SensorInfo | None = None
+        for entity in entities:
+            if isinstance(entity, aioesphomeapi.SensorInfo):
+                sensor_info = entity
+                break
+
+        assert sensor_info is not None, "Sensor entity info not found"
+        assert sensor_info.accuracy_decimals == 2, (
+            f"Expected accuracy_decimals=2, got {sensor_info.accuracy_decimals}"
+        )
+        assert sensor_info.state_class == 1, (
+            f"Expected state_class=1 (measurement), got {sensor_info.state_class}"
+        )
+        assert sensor_info.force_update is True, (
+            f"Expected force_update=True, got {sensor_info.force_update}"
+        )