Add toolchain validator factories and a native-toolchain predicate

esphome/components/esp32/__init__.py

@@ -1071,20 +1071,11 @@ def _check_esp_idf_versions(config: ConfigType) -> ConfigType:
     return config
 
 
-def _validate_toolchain(value) -> Toolchain:
-    return Toolchain(
-        cv.one_of(Toolchain.PLATFORMIO, Toolchain.ESP_IDF, lower=True)(value)
-    )
-
-
-def _resolve_toolchain(value: ConfigType) -> ConfigType:
-    # Resolve toolchain: CLI (already on CORE.toolchain) > YAML > default.
-    # Runs before _detect_variant so downstream validators can rely on
-    # CORE.toolchain instead of re-resolving it from the config dict.
-    if CORE.toolchain is None:
-        CORE.toolchain = value.get(CONF_TOOLCHAIN, Toolchain.ESP_IDF)
-    cv.check_supported_toolchain("ESP32", (Toolchain.PLATFORMIO, Toolchain.ESP_IDF))
-    return value
+_TOOLCHAINS = (Toolchain.PLATFORMIO, Toolchain.ESP_IDF)
+_validate_toolchain = cv.toolchain_enum(_TOOLCHAINS)
+# Runs before _detect_variant so downstream validators can rely on
+# CORE.toolchain instead of re-resolving it from the config dict.
+_resolve_toolchain = cv.resolve_toolchain("ESP32", _TOOLCHAINS, Toolchain.ESP_IDF)
 
 
 def _check_versions(config: ConfigType) -> ConfigType:

esphome/components/nrf52/__init__.py

@@ -125,11 +125,8 @@ def set_core_data(config: ConfigType) -> ConfigType:
     return config
 
 
-def _resolve_toolchain(config: ConfigType) -> ConfigType:
-    if CORE.toolchain is None:
-        CORE.toolchain = config.get(CONF_TOOLCHAIN, Toolchain.SDK_NRF)
-    cv.check_supported_toolchain("nRF52", (Toolchain.PLATFORMIO, Toolchain.SDK_NRF))
-    return config
+_TOOLCHAINS = (Toolchain.PLATFORMIO, Toolchain.SDK_NRF)
+_resolve_toolchain = cv.resolve_toolchain("nRF52", _TOOLCHAINS, Toolchain.SDK_NRF)
 
 
 def set_framework(config: ConfigType) -> ConfigType:
@@ -171,10 +168,7 @@ BOOTLOADERS = [
 ]
 
 
-def _validate_toolchain(value) -> Toolchain:
-    return Toolchain(
-        cv.one_of(Toolchain.PLATFORMIO, Toolchain.SDK_NRF, lower=True)(value)
-    )
+_validate_toolchain = cv.toolchain_enum(_TOOLCHAINS)
 
 
 def _detect_bootloader(config: ConfigType) -> ConfigType:

esphome/config_validation.py

@@ -53,6 +53,7 @@ from esphome.const import (
     CONF_SETUP_PRIORITY,
     CONF_STATE_TOPIC,
     CONF_SUBSCRIBE_QOS,
+    CONF_TOOLCHAIN,
     CONF_TOPIC,
     CONF_TYPE,
     CONF_TYPE_ID,
@@ -2555,20 +2556,43 @@ def check_supported_toolchain(
         )
 
 
+def toolchain_enum(supported: tuple[Toolchain, ...]):
+    """Schema validator for a platform's ``toolchain`` config key."""
+
+    def validator(value) -> Toolchain:
+        return Toolchain(one_of(*supported, lower=True)(value))
+
+    return validator
+
+
+def resolve_toolchain(
+    platform_name: str, supported: tuple[Toolchain, ...], default: Toolchain
+):
+    """Resolve ``CORE.toolchain`` (CLI > YAML > default) and reject one the
+    platform cannot serve.
+
+    Add to the platform's validation chain before anything that reads
+    ``CORE.toolchain``.
+    """
+
+    def validator(config: ConfigType) -> ConfigType:
+        if CORE.toolchain is None:
+            CORE.toolchain = config.get(CONF_TOOLCHAIN, default)
+        check_supported_toolchain(platform_name, supported)
+        return config
+
+    return validator
+
+
 def require_platformio_toolchain(platform_name: str):
     """Reject a CLI-selected toolchain other than PlatformIO.
 
     For platforms with only the PlatformIO backend; without this a
     ``--toolchain`` they cannot serve would silently build with PlatformIO.
     """
-
-    def validator(config: ConfigType) -> ConfigType:
-        if CORE.toolchain is None:
-            CORE.toolchain = Toolchain.PLATFORMIO
-        check_supported_toolchain(platform_name, (Toolchain.PLATFORMIO,))
-        return config
-
-    return validator
+    return resolve_toolchain(
+        platform_name, (Toolchain.PLATFORMIO,), Toolchain.PLATFORMIO
+    )
 
 
 def require_framework_version(

esphome/const.py

@@ -25,6 +25,12 @@ class Toolchain(StrEnum):
     ARDUINO = "arduino"
 
 
+# Toolchains that drive their build natively and never read platformio.ini.
+# SDK_NRF is absent on purpose: the zephyr backend keeps consuming
+# platformio_options.
+NATIVE_TOOLCHAINS = frozenset({Toolchain.ESP_IDF, Toolchain.ARDUINO})
+
+
 class Platform(StrEnum):
     """Platform identifiers for ESPHome."""
 

esphome/core/__init__.py

@@ -21,6 +21,7 @@ from esphome.const import (
     KEY_CORE,
     KEY_TARGET_FRAMEWORK,
     KEY_TARGET_PLATFORM,
+    NATIVE_TOOLCHAINS,
     PLATFORM_BK72XX,
     PLATFORM_ESP32,
     PLATFORM_ESP8266,
@@ -992,6 +993,12 @@ class EsphomeCore:
         """
         return self.toolchain == Toolchain.ARDUINO
 
+    @property
+    def using_native_toolchain(self):
+        """Whether the selected toolchain builds natively, without reading
+        ``platformio.ini`` (see ``NATIVE_TOOLCHAINS`` in ``esphome.const``)."""
+        return self.toolchain in NATIVE_TOOLCHAINS
+
     @property
     def using_zephyr(self):
         return self.target_framework == "zephyr"

esphome/core/config.py

@@ -557,9 +557,7 @@ def _add_library_str(lib: str) -> None:
 
 @coroutine_with_priority(CoroPriority.FINAL)
 async def _add_platformio_options(pio_options: dict[str, str | list[str]]) -> None:
-    # Every platform's toolchain validation rejects values it cannot serve,
-    # so using_toolchain_arduino by itself implies the native ESP8266 build.
-    if CORE.using_toolchain_esp_idf or CORE.using_toolchain_arduino:
+    if CORE.using_native_toolchain:
         # The native builds don't read platformio.ini; honor the options
         # with a native equivalent and warn about the rest, which would
         # otherwise be silently ignored.