[core] Add final_validate.get_declaring_config helper

esphome/final_validate.py

@@ -3,7 +3,7 @@ import contextvars
 from typing import Any
 
 import esphome.config_validation as cv
-from esphome.types import ID, ConfigFragmentType, ConfigPathType
+from esphome.types import ID, ConfigFragmentType, ConfigPathType, ConfigType
 
 
 class FinalValidateConfig(ABC):
@@ -39,6 +39,18 @@ full_config: contextvars.ContextVar[FinalValidateConfig] = contextvars.ContextVa
 )
 
 
+def get_declaring_config(
+    id_: ID, config: FinalValidateConfig | None = None
+) -> ConfigType:
+    """Return the config block that declares id_, such as a hub's own config.
+
+    Uses the full config being validated unless config is given.
+    Raises KeyError if the id was not declared.
+    """
+    fconf = full_config.get() if config is None else config
+    return fconf.get_config_for_path(fconf.get_path_for_id(id_)[:-1])
+
+
 def id_declaration_match_schema(schema):
     """A final-validation schema function that applies a schema to the outer config fragment of an
     ID declaration.

tests/unit_tests/test_final_validate.py

@@ -0,0 +1,38 @@
+"""Tests for esphome.final_validate helpers."""
+
+import pytest
+
+from esphome import final_validate as fv
+from esphome.config import Config
+from esphome.const import CONF_ID
+from esphome.core import ID
+
+
+def _config() -> tuple[Config, ID, dict]:
+    hub_id = ID("my_hub", is_declaration=True)
+    hub = {CONF_ID: hub_id, "mode": "fast"}
+    config = Config()
+    config["other"] = {"x": 1}
+    config["my_comp"] = [{"y": 2}, hub]
+    config.declare_ids.append((hub_id, ["my_comp", 1, CONF_ID]))
+    return config, hub_id, hub
+
+
+def test_returns_the_declaring_block_from_the_full_config() -> None:
+    config, hub_id, hub = _config()
+    token = fv.full_config.set(config)
+    try:
+        assert fv.get_declaring_config(hub_id) is hub
+    finally:
+        fv.full_config.reset(token)
+
+
+def test_uses_the_given_config() -> None:
+    config, hub_id, hub = _config()
+    assert fv.get_declaring_config(ID("my_hub"), config) is hub
+
+
+def test_unknown_id_raises_key_error() -> None:
+    config, _, _ = _config()
+    with pytest.raises(KeyError):
+        fv.get_declaring_config(ID("missing"), config)