[esp32] Skip full rebuild on sdkconfig change with the esp-idf toolchain (#18876)

esphome/components/esp32/__init__.py

@@ -3249,7 +3249,13 @@ def _write_sdkconfig():
     if write_file_if_changed(internal_path, contents):
         # internal changed, update real one
         write_file_if_changed(sdk_path, contents)
-        clean_build(clear_pio_cache=False)
+        if not CORE.using_toolchain_esp_idf:
+            # PIO's dependency tracking under-declares sdkconfig inputs
+            # (ldgen, linker scripts); without a clean the image can be
+            # unbootable (esphome#15336). The esp-idf toolchain tracks
+            # sdkconfig via IDF's cmake and has_outdated_files(), so a
+            # reconfigure suffices there; everything else fails safe.
+            clean_build(clear_pio_cache=False)
 
 
 def _write_idf_component_yml():

tests/unit_tests/components/esp32/test_sdkconfig.py

@@ -0,0 +1,72 @@
+"""Tests for the esp32 sdkconfig write and its toolchain-gated clean."""
+
+from __future__ import annotations
+
+import os
+from pathlib import Path
+import time
+from unittest.mock import patch
+
+import pytest
+
+from esphome.components.esp32 import _write_sdkconfig
+from esphome.components.esp32.const import KEY_SDKCONFIG_OPTIONS
+from esphome.const import KEY_CORE, KEY_ESP32, KEY_FRAMEWORK_VERSION, Toolchain
+from esphome.core import CORE
+from esphome.espidf.toolchain import has_outdated_files
+
+
+def _setup_core(tmp_path: Path, toolchain: Toolchain | None) -> None:
+    CORE.config_path = tmp_path / "test.yaml"
+    CORE.build_path = tmp_path
+    CORE.toolchain = toolchain
+    CORE.data[KEY_ESP32] = {KEY_SDKCONFIG_OPTIONS: {"CONFIG_X": "y"}}
+    CORE.data[KEY_CORE] = {KEY_FRAMEWORK_VERSION: "5.5.5"}
+
+
+def _seed_configured_build(tmp_path: Path) -> None:
+    """A settled native build: configure outputs predate what comes next."""
+    build = tmp_path / "build"
+    (build / "config").mkdir(parents=True)
+    (build / "config" / "sdkconfig.h").write_text("")
+    (build / "CMakeCache.txt").write_text("")
+    (build / "build.ninja").write_text("")
+    # Explicitly older than what the test writes next: has_outdated_files()
+    # compares st_mtime with a strict >, so same-tick writes would pass
+    past = time.time() - 60
+    for f in build.rglob("*"):
+        os.utime(f, (past, past))
+
+
+@pytest.mark.parametrize(
+    ("toolchain", "clean_expected"),
+    [(Toolchain.ESP_IDF, False), (Toolchain.PLATFORMIO, True), (None, True)],
+)
+def test_write_sdkconfig_cleans_only_on_platformio(
+    tmp_path: Path, toolchain: Toolchain | None, clean_expected: bool
+) -> None:
+    """A changed sdkconfig forces a full clean only under PlatformIO; the
+    esp-idf toolchain reconfigures via has_outdated_files() instead; an
+    unresolved toolchain fails safe onto the clean."""
+    _setup_core(tmp_path, toolchain)
+    _seed_configured_build(tmp_path)
+    with (
+        patch.object(CORE, "name", "test"),
+        patch("esphome.components.esp32.clean_build") as clean,
+    ):
+        _write_sdkconfig()
+        assert "CONFIG_X" in CORE.relative_build_path("sdkconfig.test").read_text()
+        assert clean.called is clean_expected
+        if clean_expected:
+            clean.assert_called_once_with(clear_pio_cache=False)
+        # The change must still trigger a reconfigure: the internal
+        # sdkconfig snapshot is now newer than build/CMakeCache.txt
+        assert has_outdated_files() is True
+        clean.reset_mock()
+        # A settled configure restamps the cache; an unchanged rewrite
+        # must then neither clean nor mark the build stale
+        future = time.time() + 60
+        os.utime(CORE.relative_build_path("build/CMakeCache.txt"), (future, future))
+        _write_sdkconfig()
+        clean.assert_not_called()
+        assert has_outdated_files() is False