[core] Fix platform component normalization happening too late in validation pipeline

tests/unit_tests/fixtures/ota_empty_dict.yaml

@@ -0,0 +1,17 @@
+esphome:
+  name: test-device2
+
+esp32:
+  board: esp32dev
+  framework:
+    type: esp-idf
+
+# OTA with empty dict - should be normalized
+ota: {}
+
+wifi:
+  ssid: "test"
+  password: "test"
+
+# Captive portal auto-loads ota.web_server which triggers the issue
+captive_portal:

tests/unit_tests/fixtures/ota_no_platform.yaml

@@ -0,0 +1,17 @@
+esphome:
+  name: test-device
+
+esp32:
+  board: esp32dev
+  framework:
+    type: esp-idf
+
+# OTA with no value - this should be normalized to empty list
+ota:
+
+wifi:
+  ssid: "test"
+  password: "test"
+
+# Captive portal auto-loads ota.web_server which triggers the issue
+captive_portal:

tests/unit_tests/fixtures/ota_with_platform_list.yaml

@@ -0,0 +1,19 @@
+esphome:
+  name: test-device3
+
+esp32:
+  board: esp32dev
+  framework:
+    type: esp-idf
+
+# OTA with proper list format
+ota:
+  - platform: esphome
+    password: "test123"
+
+wifi:
+  ssid: "test"
+  password: "test"
+
+# Captive portal auto-loads ota.web_server
+captive_portal:

tests/unit_tests/test_config.py

@@ -0,0 +1,271 @@
+"""Unit tests for esphome.config module."""
+
+from collections.abc import Generator
+from pathlib import Path
+from unittest.mock import MagicMock, Mock, patch
+
+import pytest
+
+from esphome import config, yaml_util
+from esphome.core import CORE
+
+
+@pytest.fixture
+def mock_get_component() -> Generator[Mock, None, None]:
+    """Fixture for mocking get_component."""
+    with patch("esphome.config.get_component") as mock_get_component:
+        yield mock_get_component
+
+
+@pytest.fixture
+def mock_get_platform() -> Generator[Mock, None, None]:
+    """Fixture for mocking get_platform."""
+    with patch("esphome.config.get_platform") as mock_get_platform:
+        # Default mock platform
+        mock_get_platform.return_value = MagicMock()
+        yield mock_get_platform
+
+
+@pytest.fixture
+def fixtures_dir() -> Path:
+    """Get the fixtures directory."""
+    return Path(__file__).parent / "fixtures"
+
+
+def test_iter_components_handles_non_list_platform_component(
+    mock_get_component: Mock,
+) -> None:
+    """Test that iter_components handles platform components that have been normalized to empty list."""
+    # After LoadValidationStep normalization, platform components without config
+    # are converted to empty list
+    test_config = {
+        "ota": [],  # Normalized from None/dict to empty list by LoadValidationStep
+        "wifi": {"ssid": "test"},
+    }
+
+    # Set up mock components
+    components = {
+        "ota": MagicMock(is_platform_component=True),
+        "wifi": MagicMock(is_platform_component=False),
+    }
+
+    mock_get_component.side_effect = lambda domain: components.get(
+        domain, MagicMock(is_platform_component=False)
+    )
+
+    # This should not raise TypeError
+    components_list = list(config.iter_components(test_config))
+
+    # Verify we got the expected components
+    assert len(components_list) == 2  # ota and wifi (ota has no platforms)
+
+
+def test_iter_component_configs_handles_non_list_platform_component(
+    mock_get_component: Mock,
+    mock_get_platform: Mock,
+) -> None:
+    """Test that iter_component_configs handles platform components that have been normalized."""
+
+    # After LoadValidationStep normalization
+    test_config = {
+        "ota": [],  # Normalized from None/dict to empty list by LoadValidationStep
+        "one_wire": [  # List config for platform component
+            {"platform": "gpio", "pin": 10}
+        ],
+    }
+
+    # Set up mock components
+    components: dict[str, Mock] = {
+        "ota": MagicMock(is_platform_component=True, multi_conf=False),
+        "one_wire": MagicMock(is_platform_component=True, multi_conf=False),
+    }
+
+    # Default mock for unknown components
+    default_mock = MagicMock(is_platform_component=False, multi_conf=False)
+
+    mock_get_component.side_effect = lambda domain: components.get(domain, default_mock)
+
+    # This should not raise TypeError
+    configs = list(config.iter_component_configs(test_config))
+
+    # Should have 3 items: ota (empty list), one_wire, and one_wire.gpio
+    assert len(configs) == 3
+
+    # Check the domains
+    domains = [c[0] for c in configs]
+    assert "ota" in domains
+    assert "one_wire" in domains
+    assert "one_wire.gpio" in domains
+
+
+def test_iter_components_with_valid_platform_list(
+    mock_get_component: Mock,
+    mock_get_platform: Mock,
+) -> None:
+    """Test that iter_components works correctly with valid platform component list."""
+
+    # Create a mock component that is a platform component
+    mock_component = MagicMock()
+    mock_component.is_platform_component = True
+
+    # Create test config with proper list format
+    test_config = {
+        "sensor": [
+            {"platform": "dht", "pin": 5},
+            {"platform": "bme280", "address": 0x76},
+        ],
+    }
+
+    mock_get_component.return_value = mock_component
+
+    # Get all components
+    components = list(config.iter_components(test_config))
+
+    # Should have 3 items: sensor, sensor.dht, sensor.bme280
+    assert len(components) == 3
+
+    # Check the domains
+    domains = [c[0] for c in components]
+    assert "sensor" in domains
+    assert "sensor.dht" in domains
+    assert "sensor.bme280" in domains
+
+
+def test_ota_with_proper_platform_list(
+    mock_get_component: Mock,
+    mock_get_platform: Mock,
+) -> None:
+    """Test that OTA component works correctly when configured as a list with platforms."""
+
+    # Create test config where ota is properly configured as a list
+    test_config = {
+        "ota": [
+            {"platform": "esphome", "password": "test123"},
+        ],
+    }
+
+    mock_get_component.return_value = MagicMock(is_platform_component=True)
+
+    # This should work without TypeError
+    components = list(config.iter_components(test_config))
+
+    # Should have 2 items: ota and ota.esphome
+    assert len(components) == 2
+
+    # Check the domains
+    domains = [c[0] for c in components]
+    assert "ota" in domains
+    assert "ota.esphome" in domains
+
+
+def test_ota_component_configs_with_proper_platform_list(
+    mock_get_component: Mock,
+    mock_get_platform: Mock,
+) -> None:
+    """Test that iter_component_configs handles OTA properly configured as a list."""
+
+    # Create test config where ota is properly configured as a list
+    test_config = {
+        "ota": [
+            {"platform": "esphome", "password": "test123", "id": "my_ota"},
+        ],
+    }
+
+    mock_get_component.return_value = MagicMock(
+        is_platform_component=True, multi_conf=False
+    )
+
+    # This should work without TypeError
+    configs = list(config.iter_component_configs(test_config))
+
+    # Should have 2 items: ota config and ota.esphome platform config
+    assert len(configs) == 2
+
+    # Check the domains and configs
+    assert configs[0][0] == "ota"
+    assert configs[0][2] == test_config["ota"]  # The list itself
+
+    assert configs[1][0] == "ota.esphome"
+    assert configs[1][2]["platform"] == "esphome"
+    assert configs[1][2]["password"] == "test123"
+
+
+def test_iter_component_configs_with_multi_conf(mock_get_component: Mock) -> None:
+    """Test that iter_component_configs handles multi_conf components correctly."""
+    # Create test config
+    test_config = {
+        "switch": [
+            {"name": "Switch 1"},
+            {"name": "Switch 2"},
+        ],
+    }
+
+    # Set up mock component with multi_conf
+    mock_get_component.return_value = MagicMock(
+        is_platform_component=False, multi_conf=True
+    )
+
+    # Get all configs
+    configs = list(config.iter_component_configs(test_config))
+
+    # Should have 2 items (one for each switch)
+    assert len(configs) == 2
+
+    # Both should be for "switch" domain
+    for domain, component, conf in configs:
+        assert domain == "switch"
+        assert "name" in conf
+
+
+def test_ota_no_platform_with_captive_portal(fixtures_dir: Path) -> None:
+    """Test OTA with no platform (ota:) gets normalized when captive_portal auto-loads."""
+    # Set up CORE config path
+    CORE.config_path = fixtures_dir / "dummy.yaml"
+
+    # Load config with OTA having no value (ota:)
+    config_file = fixtures_dir / "ota_no_platform.yaml"
+    raw_config = yaml_util.load_yaml(config_file)
+    result = config.validate_config(raw_config, {})
+
+    # Check that OTA was normalized to a list and captive_portal added web_server
+    assert "ota" in result
+    assert isinstance(result["ota"], list), f"Expected list, got {type(result['ota'])}"
+    # After captive_portal auto-loads, OTA should have web_server platform
+    platforms = {p.get("platform") for p in result["ota"]}
+    assert "web_server" in platforms, f"Expected web_server platform in {platforms}"
+
+
+def test_ota_empty_dict_with_captive_portal(fixtures_dir: Path) -> None:
+    """Test OTA with empty dict ({}) gets normalized when captive_portal auto-loads."""
+    # Set up CORE config path
+    CORE.config_path = fixtures_dir / "dummy.yaml"
+
+    # Load config with OTA having empty dict (ota: {})
+    config_file = fixtures_dir / "ota_empty_dict.yaml"
+    raw_config = yaml_util.load_yaml(config_file)
+    result = config.validate_config(raw_config, {})
+
+    # Check that OTA was normalized to a list and captive_portal added web_server
+    assert "ota" in result
+    assert isinstance(result["ota"], list), f"Expected list, got {type(result['ota'])}"
+    # The empty dict gets normalized and web_server is added
+    platforms = {p.get("platform") for p in result["ota"]}
+    assert "web_server" in platforms, f"Expected web_server platform in {platforms}"
+
+
+def test_ota_with_platform_list_and_captive_portal(fixtures_dir: Path) -> None:
+    """Test OTA with proper platform list remains valid when captive_portal auto-loads."""
+    # Set up CORE config path
+    CORE.config_path = fixtures_dir / "dummy.yaml"
+
+    # Load config with OTA having proper list format
+    config_file = fixtures_dir / "ota_with_platform_list.yaml"
+    raw_config = yaml_util.load_yaml(config_file)
+    result = config.validate_config(raw_config, {})
+
+    # Check that OTA remains a list with both esphome and web_server platforms
+    assert "ota" in result
+    assert isinstance(result["ota"], list), f"Expected list, got {type(result['ota'])}"
+    platforms = {p.get("platform") for p in result["ota"]}
+    assert "esphome" in platforms, f"Expected esphome platform in {platforms}"
+    assert "web_server" in platforms, f"Expected web_server platform in {platforms}"