Add support for constant selector (#89573)

* Add support for constant selector

* Adapt to frontend PR changes

homeassistant/helpers/selector.py

@@ -358,6 +358,38 @@ class ConfigEntrySelector(Selector[ConfigEntrySelectorConfig]):
         return config
 
 
+class ConstantSelectorConfig(TypedDict, total=False):
+    """Class to represent a constant selector config."""
+
+    label: str
+    translation_key: str
+    value: str | int | bool
+
+
+@SELECTORS.register("constant")
+class ConstantSelector(Selector[ConstantSelectorConfig]):
+    """Constant selector."""
+
+    selector_type = "constant"
+
+    CONFIG_SCHEMA = vol.Schema(
+        {
+            vol.Optional("label"): str,
+            vol.Optional("translation_key"): cv.string,
+            vol.Required("value"): vol.Any(str, int, bool),
+        }
+    )
+
+    def __init__(self, config: ConstantSelectorConfig | None = None) -> None:
+        """Instantiate a selector."""
+        super().__init__(config)
+
+    def __call__(self, data: Any) -> Any:
+        """Validate the passed selection."""
+        vol.Schema(self.config["value"])(data)
+        return self.config["value"]
+
+
 class DateSelectorConfig(TypedDict):
     """Class to represent a date selector config."""
 

tests/helpers/test_selector.py

@@ -836,3 +836,57 @@ def test_file_selector_schema(schema, valid_selections, invalid_selections) -> N
     """Test file selector."""
 
     _test_selector("file", schema, valid_selections, invalid_selections)
+
+
+@pytest.mark.parametrize(
+    ("schema", "valid_selections", "invalid_selections"),
+    (
+        (
+            {"value": True, "label": "Blah"},
+            (True, 1),
+            (None, False, 0, "abc", "def"),
+        ),
+        (
+            {"value": False},
+            (False, 0),
+            (None, True, 1, "abc", "def"),
+        ),
+        (
+            {"value": 0},
+            (0, False),
+            (None, True, 1, "abc", "def"),
+        ),
+        (
+            {"value": 1},
+            (1, True),
+            (None, False, 0, "abc", "def"),
+        ),
+        (
+            {"value": 4},
+            (4,),
+            (None, False, True, 0, 1, "abc", "def"),
+        ),
+        (
+            {"value": "dog"},
+            ("dog",),
+            (None, False, True, 0, 1, "abc", "def"),
+        ),
+    ),
+)
+def test_constant_selector_schema(schema, valid_selections, invalid_selections) -> None:
+    """Test constant selector."""
+    _test_selector("constant", schema, valid_selections, invalid_selections)
+
+
+@pytest.mark.parametrize(
+    "schema",
+    (
+        {},  # Value is mandatory
+        {"value": []},  # Value must be str, int or bool
+        {"value": 123, "label": 123},  # Label must be str
+    ),
+)
+def test_constant_selector_schema_error(schema) -> None:
+    """Test constant selector."""
+    with pytest.raises(vol.Invalid):
+        selector.validate_selector({"constant": schema})