From d01d2189b9266c4c2dc745fac67ce073abb4de89 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Sat, 21 Feb 2026 01:22:18 -0600
Subject: [PATCH] Guard device_class/UoM fields and lookups with #ifdef like
 icon

---
 esphome/core/entity_base.cpp   | 12 +++++++++++-
 esphome/core/entity_base.h     | 14 +++++++++++++-
 esphome/core/entity_helpers.py | 12 ++++++++----
 3 files changed, 32 insertions(+), 6 deletions(-)

diff --git a/esphome/core/entity_base.cpp b/esphome/core/entity_base.cpp
index 31e9618640..eafc04f92a 100644
--- a/esphome/core/entity_base.cpp
+++ b/esphome/core/entity_base.cpp
@@ -52,12 +52,22 @@ __attribute__((weak)) const char *entity_icon_lookup(uint8_t) { return ""; }
 
 // Entity device class (from index)
 StringRef EntityBase::get_device_class_ref() const {
+#ifdef USE_ENTITY_DEVICE_CLASS
   return StringRef(entity_device_class_lookup(this->device_class_idx_));
+#else
+  return StringRef(entity_device_class_lookup(0));
+#endif
 }
 std::string EntityBase::get_device_class() const { return std::string(this->get_device_class_ref().c_str()); }
 
 // Entity unit of measurement (from index)
-StringRef EntityBase::get_unit_of_measurement_ref() const { return StringRef(entity_uom_lookup(this->uom_idx_)); }
+StringRef EntityBase::get_unit_of_measurement_ref() const {
+#ifdef USE_ENTITY_UNIT_OF_MEASUREMENT
+  return StringRef(entity_uom_lookup(this->uom_idx_));
+#else
+  return StringRef(entity_uom_lookup(0));
+#endif
+}
 std::string EntityBase::get_unit_of_measurement() const {
   return std::string(this->get_unit_of_measurement_ref().c_str());
 }
diff --git a/esphome/core/entity_base.h b/esphome/core/entity_base.h
index e67f16422a..042eebb40f 100644
--- a/esphome/core/entity_base.h
+++ b/esphome/core/entity_base.h
@@ -97,10 +97,16 @@ class EntityBase {
 
   // Set entity string table indices — one call per entity from codegen.
   // Packed: [23..16] icon | [15..8] UoM | [7..0] device_class (each 8 bits)
-  void set_entity_strings(uint32_t packed) {
+  void set_entity_strings([[maybe_unused]] uint32_t packed) {
+#ifdef USE_ENTITY_DEVICE_CLASS
     this->device_class_idx_ = packed & 0xFF;
+#endif
+#ifdef USE_ENTITY_UNIT_OF_MEASUREMENT
     this->uom_idx_ = (packed >> 8) & 0xFF;
+#endif
+#ifdef USE_ENTITY_ICON
     this->icon_idx_ = (packed >> 16) & 0xFF;
+#endif
   }
 
   // Get device class as StringRef (from packed index)
@@ -209,9 +215,15 @@ class EntityBase {
     uint8_t reserved : 2;         // Reserved for future use
   } flags_{};
   // String table indices — packed into the 3 padding bytes after flags_
+#ifdef USE_ENTITY_DEVICE_CLASS
   uint8_t device_class_idx_{};
+#endif
+#ifdef USE_ENTITY_UNIT_OF_MEASUREMENT
   uint8_t uom_idx_{};
+#endif
+#ifdef USE_ENTITY_ICON
   uint8_t icon_idx_{};
+#endif
 };
 
 /// Log entity icon if set (for use in dump_config)
diff --git a/esphome/core/entity_helpers.py b/esphome/core/entity_helpers.py
index cc435e7c47..fd151d82d9 100644
--- a/esphome/core/entity_helpers.py
+++ b/esphome/core/entity_helpers.py
@@ -165,14 +165,18 @@ def register_icon(value: str) -> int:
 
 def setup_device_class(config: ConfigType) -> None:
     """Register config's device_class and store its index for finalize_entity_strings."""
-    config[_KEY_DC_IDX] = register_device_class(config.get(CONF_DEVICE_CLASS, ""))
+    idx = register_device_class(config.get(CONF_DEVICE_CLASS, ""))
+    if idx:
+        cg.add_define("USE_ENTITY_DEVICE_CLASS")
+    config[_KEY_DC_IDX] = idx
 
 
 def setup_unit_of_measurement(config: ConfigType) -> None:
     """Register config's unit_of_measurement and store its index for finalize_entity_strings."""
-    config[_KEY_UOM_IDX] = register_unit_of_measurement(
-        config.get(CONF_UNIT_OF_MEASUREMENT, "")
-    )
+    idx = register_unit_of_measurement(config.get(CONF_UNIT_OF_MEASUREMENT, ""))
+    if idx:
+        cg.add_define("USE_ENTITY_UNIT_OF_MEASUREMENT")
+    config[_KEY_UOM_IDX] = idx
 
 
 def finalize_entity_strings(var: MockObj, config: ConfigType) -> None: