From 12c35c15451c9038c0ca8b4311a3589cd0771a98 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Mon, 12 Oct 2026 16:53:49 -1000
Subject: [PATCH] Compute the object id hash when an external caller passes 0

---
 esphome/core/entity_base.cpp                    |  9 ++++++++-
 esphome/core/helpers.h                          | 12 ++++++++++++
 tests/components/core/test_entity_base_name.cpp | 17 +++++++++++++++++
 3 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/esphome/core/entity_base.cpp b/esphome/core/entity_base.cpp
index e1ba7593d3..7bf55c0354 100644
--- a/esphome/core/entity_base.cpp
+++ b/esphome/core/entity_base.cpp
@@ -68,7 +68,14 @@ void EntityBase::configure_entity_(const char *name, uint32_t object_id_hash, ui
     this->object_id_hash_ = fnv1_hash_object_id(fallback.c_str(), fallback.size());
   } else {
     this->flags_.has_own_name = true;
-    // Static name - codegen precomputes the hash
+    // Static name - codegen precomputes the hash; external register_* callers may pass 0
+    if (object_id_hash == 0) {
+#ifdef USE_ESP8266
+      object_id_hash = fnv1_hash_object_id_P(this->name_.progmem_ptr(), this->name_.size());
+#else
+      object_id_hash = fnv1_hash_object_id(this->name_.progmem_ptr(), this->name_.size());
+#endif
+    }
     this->object_id_hash_ = object_id_hash;
   }
   // Unpack entity string table indices and flags from entity_fields.
diff --git a/esphome/core/helpers.h b/esphome/core/helpers.h
index bcb03b010f..2d6cd1a96d 100644
--- a/esphome/core/helpers.h
+++ b/esphome/core/helpers.h
@@ -1145,6 +1145,18 @@ inline uint32_t fnv1_hash_object_id(const char *str, size_t len) {
   return hash;
 }
 
+#ifdef USE_ESP8266
+/// fnv1_hash_object_id() for a string in flash (PROGMEM).
+inline uint32_t fnv1_hash_object_id_P(PGM_P str, size_t len) {
+  uint32_t hash = FNV1_OFFSET_BASIS;
+  for (size_t i = 0; i < len; i++) {
+    hash *= FNV1_PRIME;
+    hash ^= static_cast<uint8_t>(to_sanitized_char(to_snake_case_char(static_cast<char>(pgm_read_byte(str + i)))));
+  }
+  return hash;
+}
+#endif
+
 #ifdef USE_ESP8266
 // ESP8266: Use vsnprintf_P to keep format strings in flash (PROGMEM)
 // Format strings must be wrapped with PSTR() macro
diff --git a/tests/components/core/test_entity_base_name.cpp b/tests/components/core/test_entity_base_name.cpp
index 18af5278a1..cf2af3e7ca 100644
--- a/tests/components/core/test_entity_base_name.cpp
+++ b/tests/components/core/test_entity_base_name.cpp
@@ -13,4 +13,21 @@ namespace esphome::core::testing {
 static_assert(std::is_same_v<decltype(std::declval<const EntityBase &>().get_name()), const StringRef &>);
 #pragma GCC diagnostic pop
 
+class TestEntity : public EntityBase {
+ public:
+  void configure(const char *name, uint32_t object_id_hash) { this->configure_entity_(name, object_id_hash, 0); }
+};
+
+TEST(EntityBaseName, ZeroHashIsComputedFromTheName) {
+  TestEntity entity;
+  entity.configure("Living Room Temp", 0);
+  EXPECT_EQ(entity.get_object_id_hash(), fnv1_hash_object_id("Living Room Temp", 16));
+}
+
+TEST(EntityBaseName, PrecomputedHashIsKept) {
+  TestEntity entity;
+  entity.configure("Living Room Temp", 0x1234);
+  EXPECT_EQ(entity.get_object_id_hash(), 0x1234u);
+}
+
 }  // namespace esphome::core::testing