[lvgl] Build widget update action schemas lazily (#16569)

Co-authored-by: Clyde Stubbs <2366188+clydebarrow@users.noreply.github.com>

tests/component_tests/lvgl/test_update_action_lazy.py

@@ -0,0 +1,53 @@
+"""Tests for lvgl.<widget>.update lazy schema build."""
+
+from __future__ import annotations
+
+from unittest.mock import patch
+
+from esphome.automation import ACTION_REGISTRY
+import esphome.components.lvgl  # noqa: F401
+from esphome.components.lvgl.schemas import WIDGET_TYPES
+from esphome.components.lvgl.widgets import _update_action_schema
+from esphome.config_validation import Schema
+
+
+def _widget_type(name: str = "obj"):
+    wt = WIDGET_TYPES.get(name)
+    assert wt is not None, f"widget type {name!r} not registered"
+    return wt
+
+
+def test_registry_entry_uses_lazy_validator() -> None:
+    entry = ACTION_REGISTRY["lvgl.label.update"]
+    assert callable(entry.raw_schema)
+    assert not isinstance(entry.raw_schema, Schema)
+
+
+def test_lazy_validator_defers_build_until_first_call() -> None:
+    wt = _widget_type("label")
+    with patch(
+        "esphome.components.lvgl.widgets._build_update_schema",
+        wraps=lambda w: Schema({}),
+    ) as build_mock:
+        validator = _update_action_schema(wt)
+        assert build_mock.call_count == 0
+        validator({})
+        assert build_mock.call_count == 1
+        validator({})
+        assert build_mock.call_count == 1
+
+
+def test_eager_build_when_schema_extraction_enabled() -> None:
+    wt = _widget_type("label")
+    with patch("esphome.components.lvgl.widgets.EnableSchemaExtraction", True):
+        result = _update_action_schema(wt)
+    assert isinstance(result, Schema)
+
+
+def test_lazy_and_eager_produce_equivalent_validation() -> None:
+    wt = _widget_type("label")
+    with patch("esphome.components.lvgl.widgets.EnableSchemaExtraction", True):
+        eager = _update_action_schema(wt)
+    lazy = _update_action_schema(wt)
+    sample = {"id": "label_id"}
+    assert lazy(sample) == eager(sample)