[core] Fix WiFi connection in safe mode (#16269)

Co-authored-by: J. Nick Koston <nick@home-assistant.io>
Co-authored-by: pre-commit-ci-lite[bot] <117423508+pre-commit-ci-lite[bot]@users.noreply.github.com>
Co-authored-by: J. Nick Koston <nick@koston.org>

tests/unit_tests/core/test_config.py

@@ -10,6 +10,7 @@ from unittest.mock import MagicMock, Mock, patch
 import pytest
 
 from esphome import config_validation as cv, core
+from esphome.components.safe_mode import to_code as safe_mode_to_code
 from esphome.const import (
     CONF_AREA,
     CONF_AREAS,
@@ -312,6 +313,75 @@ def test_add_platform_defines_priority() -> None:
     )
 
 
+def test_to_code_priority_above_safe_mode() -> None:
+    """Test that core to_code emits the looping_components_ init before safe_mode.
+
+    Regression test for https://github.com/esphome/esphome/issues/16262.
+    safe_mode emits an `if (should_enter_safe_mode(...)) return;` line in main()
+    at APPLICATION priority. The `App.looping_components_.init(...)` call must be
+    emitted at a higher priority than APPLICATION so it lands in main() before
+    the early return; otherwise the FixedVector is never sized when safe mode is
+    active and loop() never runs (Wi-Fi never connects).
+    """
+    assert config.to_code.priority > safe_mode_to_code.priority, (
+        f"core to_code priority ({config.to_code.priority}) must be greater than "
+        f"safe_mode to_code priority ({safe_mode_to_code.priority}) so that "
+        "App.looping_components_.init() is emitted before safe_mode's early return"
+    )
+
+
+@pytest.mark.asyncio
+async def test_add_looping_components_handles_empty_entries() -> None:
+    """Test that _add_looping_components emits a valid constexpr when there are
+    no looping component entries.
+
+    With zero entries the generated constexpr must still be syntactically valid
+    C++ (`= 0;`), not an empty expression (`= ;`). This guards the empty-list
+    case that would otherwise produce uncompilable main.cpp output.
+    """
+    CORE.data["looping_component_entries"] = []
+
+    await config._add_looping_components()
+
+    constexpr_lines = [
+        str(s)
+        for s in CORE.global_statements
+        if "ESPHOME_LOOPING_COMPONENT_COUNT" in str(s)
+    ]
+    assert len(constexpr_lines) == 1
+    text = constexpr_lines[0]
+    assert "static constexpr size_t ESPHOME_LOOPING_COMPONENT_COUNT" in text
+    # The right-hand side must contain a literal `0`, not be empty.
+    rhs = text.split("=", 1)[1]
+    assert "0" in rhs
+    assert rhs.strip().rstrip(";").strip(), (
+        f"constexpr right-hand side must not be empty, got: {text!r}"
+    )
+
+
+@pytest.mark.asyncio
+async def test_add_looping_components_with_entries() -> None:
+    """Test that _add_looping_components builds a HasLoopOverride sum from entries."""
+    CORE.data["looping_component_entries"] = [
+        "esphome::wifi::WiFiComponent",
+        "esphome::logger::Logger",
+        "esphome::wifi::WiFiComponent",
+    ]
+
+    await config._add_looping_components()
+
+    constexpr_lines = [
+        str(s)
+        for s in CORE.global_statements
+        if "ESPHOME_LOOPING_COMPONENT_COUNT" in str(s)
+    ]
+    assert len(constexpr_lines) == 1
+    text = constexpr_lines[0]
+    # Deduplicated by type, with per-type counts as multiplier.
+    assert "(2 * HasLoopOverride<esphome::wifi::WiFiComponent>::value)" in text
+    assert "(1 * HasLoopOverride<esphome::logger::Logger>::value)" in text
+
+
 def test_valid_include_with_angle_brackets() -> None:
     """Test valid_include accepts angle bracket includes."""
     assert valid_include("<ArduinoJson.h>") == "<ArduinoJson.h>"