Speed up validating domains in templates (#92975)

This path gets called quite a bit since most templates
access the state via states.DOMAIN...

homeassistant/core.py

@@ -161,9 +161,19 @@ def split_entity_id(entity_id: str) -> tuple[str, str]:
     return domain, object_id
 
 
-VALID_ENTITY_ID = re.compile(r"^(?!.+__)(?!_)[\da-z_]+(?<!_)\.(?!_)[\da-z_]+(?<!_)$")
+_OBJECT_ID = r"(?!_)[\da-z_]+(?<!_)"
+_DOMAIN = r"(?!.+__)" + _OBJECT_ID
+VALID_DOMAIN = re.compile(r"^" + _DOMAIN + r"$")
+VALID_ENTITY_ID = re.compile(r"^" + _DOMAIN + r"\." + _OBJECT_ID + r"$")
 
 
+@functools.lru_cache(64)
+def valid_domain(domain: str) -> bool:
+    """Test if a domain a valid format."""
+    return VALID_DOMAIN.match(domain) is not None
+
+
+@functools.lru_cache(64)
 def valid_entity_id(entity_id: str) -> bool:
     """Test if an entity ID is a valid format.
 

homeassistant/helpers/template.py

@@ -63,6 +63,7 @@
     State,
     callback,
     split_entity_id,
+    valid_domain,
     valid_entity_id,
 )
 from homeassistant.exceptions import TemplateError
@@ -796,7 +797,7 @@ def __getattr__(self, name):
         if name in _RESERVED_NAMES:
             return None
 
-        if not valid_entity_id(f"{name}.entity"):
+        if not valid_domain(name):
             raise TemplateError(f"Invalid domain name '{name}'")
 
         return _domain_states(self._hass, name)

tests/test_core.py

@@ -1384,6 +1384,32 @@ def test_valid_entity_id() -> None:
         assert ha.valid_entity_id(valid), valid
 
 
+def test_valid_domain() -> None:
+    """Test valid domain."""
+    for invalid in [
+        "_light",
+        ".kitchen",
+        ".light.kitchen",
+        "light_.kitchen",
+        "._kitchen",
+        "light.",
+        "light.kitchen__ceiling",
+        "light.kitchen_yo_",
+        "light.kitchen.",
+        "Light",
+    ]:
+        assert not ha.valid_domain(invalid), invalid
+
+    for valid in [
+        "1",
+        "1light",
+        "a",
+        "input_boolean",
+        "light",
+    ]:
+        assert ha.valid_domain(valid), valid
+
+
 async def test_additional_data_in_core_config(
     hass: HomeAssistant, hass_storage: dict[str, Any]
 ) -> None: