From 9e3869ae1c08f5293a2b130999843118395411d6 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Fri, 29 Dec 2023 17:10:40 -1000
Subject: [PATCH] Avoid recreating ReadOnly dicts when attributes do not change
 (#106687)

---
 homeassistant/core.py | 13 ++++++++++++-
 tests/test_core.py    | 20 ++++++++++++++++++++
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/homeassistant/core.py b/homeassistant/core.py
index 51cb3d4e496..cb17bd55805 100644
--- a/homeassistant/core.py
+++ b/homeassistant/core.py
@@ -1409,7 +1409,13 @@ class State:
 
         self.entity_id = entity_id
         self.state = state
-        self.attributes = ReadOnlyDict(attributes or {})
+        # State only creates and expects a ReadOnlyDict so
+        # there is no need to check for subclassing with
+        # isinstance here so we can use the faster type check.
+        if type(attributes) is not ReadOnlyDict:  # noqa: E721
+            self.attributes = ReadOnlyDict(attributes or {})
+        else:
+            self.attributes = attributes
         self.last_updated = last_updated or dt_util.utcnow()
         self.last_changed = last_changed or self.last_updated
         self.context = context or Context()
@@ -1828,6 +1834,11 @@ class StateMachine:
         else:
             now = dt_util.utcnow()
 
+        if same_attr:
+            if TYPE_CHECKING:
+                assert old_state is not None
+            attributes = old_state.attributes
+
         state = State(
             entity_id,
             new_state,
diff --git a/tests/test_core.py b/tests/test_core.py
index 90b87068a5d..da76961c5be 100644
--- a/tests/test_core.py
+++ b/tests/test_core.py
@@ -1157,6 +1157,26 @@ async def test_statemachine_force_update(hass: HomeAssistant) -> None:
     assert len(events) == 1
 
 
+async def test_statemachine_avoids_updating_attributes(hass: HomeAssistant) -> None:
+    """Test async_set avoids recreating ReadOnly dicts when possible."""
+    attrs = {"some_attr": "attr_value"}
+
+    hass.states.async_set("light.bowl", "off", attrs)
+    await hass.async_block_till_done()
+
+    state = hass.states.get("light.bowl")
+    assert state.attributes == attrs
+
+    hass.states.async_set("light.bowl", "on", attrs)
+    await hass.async_block_till_done()
+
+    new_state = hass.states.get("light.bowl")
+    assert new_state.attributes == attrs
+
+    assert new_state.attributes is state.attributes
+    assert isinstance(new_state.attributes, ReadOnlyDict)
+
+
 def test_service_call_repr() -> None:
     """Test ServiceCall repr."""
     call = ha.ServiceCall("homeassistant", "start")