[esp32] Make ESP-IDF builds reproducible (#16008)

Co-authored-by: J. Nick Koston <nick@koston.org>

esphome/components/esp32/__init__.py

@@ -1729,6 +1729,10 @@ async def to_code(config):
         cg.add_build_flag("-DUSE_ESP32_FRAMEWORK_ESP_IDF")
         if use_platformio:
             cg.add_platformio_option("framework", "espidf")
+            # Strip volatile build path/time metadata from PlatformIO-managed
+            # ESP-IDF builds so equivalent projects can produce reproducible
+            # outputs and downstream tooling can safely reuse artifacts.
+            add_idf_sdkconfig_option("CONFIG_APP_REPRODUCIBLE_BUILD", True)
 
         # Wrap std::__throw_* functions to abort immediately, eliminating ~3KB of
         # exception class overhead. See throw_stubs.cpp for implementation.

tests/component_tests/esp32/config/reproducible_build.yaml

@@ -0,0 +1,8 @@
+esphome:
+  name: test
+
+esp32:
+  board: esp32dev
+  variant: esp32
+  framework:
+    type: esp-idf

tests/component_tests/esp32/test_esp32.py

@@ -232,3 +232,14 @@ def test_execute_from_psram_disabled_sdkconfig(
     assert "CONFIG_SPIRAM_FETCH_INSTRUCTIONS" not in sdkconfig
     assert "CONFIG_SPIRAM_RODATA" not in sdkconfig
     assert "CONFIG_SPIRAM_XIP_FROM_PSRAM" not in sdkconfig
+
+
+def test_platformio_idf_enables_reproducible_build(
+    generate_main: Callable[[str | Path], str],
+    component_config_path: Callable[[str], Path],
+) -> None:
+    """Test PlatformIO ESP-IDF builds enable reproducible app metadata."""
+    generate_main(component_config_path("reproducible_build.yaml"))
+
+    sdkconfig = CORE.data[KEY_ESP32][KEY_SDKCONFIG_OPTIONS]
+    assert sdkconfig.get("CONFIG_APP_REPRODUCIBLE_BUILD") is True