Reject unsupported toolchains on the PlatformIO-only platforms and warn on empty srcFilter matches

esphome/arduino8266/component.py

@@ -123,6 +123,13 @@ def _library_info(name: str, read_path: Path, data: dict) -> ArduinoLibrary:
         for f in collect_filtered_files(read_path / src_dir, src_filter)
         if (path := Path(f)).suffix in SRC_FILE_EXTENSIONS
     )
+    if not lib.sources and ("srcFilter" in build or "srcDir" in build):
+        # A default probe finding nothing is a header-only library; a
+        # declared filter matching nothing is a manifest/tree problem.
+        _LOGGER.warning(
+            "Library %s declares srcFilter/srcDir but no source files matched",
+            name,
+        )
     return lib
 
 

esphome/components/host/__init__.py

@@ -37,6 +37,7 @@ CONFIG_SCHEMA = cv.All(
         }
     ),
     set_core_data,
+    cv.require_platformio_toolchain("host"),
 )
 
 

esphome/components/libretiny/__init__.py

@@ -315,6 +315,7 @@ BASE_SCHEMA = cv.Schema(
 
 BASE_SCHEMA.add_extra(_detect_variant)
 BASE_SCHEMA.add_extra(_update_core_data)
+BASE_SCHEMA.add_extra(cv.require_platformio_toolchain("LibreTiny"))
 
 
 def _configure_lwip(config: dict) -> None:

esphome/components/rp2/__init__.py

@@ -312,6 +312,7 @@ CONFIG_SCHEMA = cv.All(
     cv.has_at_least_one_key(CONF_BOARD, CONF_VARIANT),
     _detect_variant,
     set_core_data,
+    cv.require_platformio_toolchain("RP2"),
 )
 
 

esphome/config_validation.py

@@ -2532,6 +2532,28 @@ def platformio_version_constraint(value):
     return constraints
 
 
+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):
+        from esphome.const import Toolchain
+
+        if CORE.toolchain is None:
+            CORE.toolchain = Toolchain.PLATFORMIO
+        if CORE.toolchain != Toolchain.PLATFORMIO:
+            raise Invalid(
+                f"Unsupported toolchain '{CORE.toolchain.value}' for "
+                f"{platform_name}. The only supported toolchain is 'platformio'."
+            )
+        return config
+
+    return validator
+
+
 def require_framework_version(
     *,
     max_version=False,

tests/unit_tests/test_arduino8266_component.py

@@ -96,6 +96,27 @@ def test_library_info_missing_link_dir_warns(
     assert lib.link_dirs == [(read_path / "missing_blobs").resolve()]
 
 
+def test_library_info_declared_filter_matches_nothing_warns(
+    tmp_path: Path, caplog: pytest.LogCaptureFixture
+) -> None:
+    read_path = tmp_path / "lib"
+    (read_path / "src").mkdir(parents=True)
+    data = {"build": {"srcFilter": ["+<nothing/*>"]}}
+    lib = component._library_info("x", read_path, data)
+    assert not lib.sources
+    assert "declares srcFilter/srcDir but no source files matched" in caplog.text
+
+
+def test_library_info_header_only_does_not_warn(
+    tmp_path: Path, caplog: pytest.LogCaptureFixture
+) -> None:
+    read_path = tmp_path / "lib"
+    (read_path / "src").mkdir(parents=True)
+    lib = component._library_info("x", read_path, {})
+    assert not lib.sources
+    assert "no source files matched" not in caplog.text
+
+
 def test_library_info_no_src_dir(tmp_path: Path) -> None:
     read_path = tmp_path / "empty"
     read_path.mkdir()

tests/unit_tests/test_config_validation.py

@@ -3165,3 +3165,19 @@ def test_file__remapped_path_is_directory_raises(setup_core: Path) -> None:
 
     with pytest.raises(Invalid, match="is not a file"):
         cv.file_("/original/config/headers")
+
+
+def test_require_platformio_toolchain() -> None:
+    """Platforms with only the PlatformIO backend reject other toolchains."""
+    from esphome.const import Toolchain
+    from esphome.core import CORE
+
+    validator = cv.require_platformio_toolchain("RP2")
+    CORE.toolchain = None
+    config: dict = {}
+    assert validator(config) is config
+    assert CORE.toolchain == Toolchain.PLATFORMIO
+
+    CORE.toolchain = Toolchain.ARDUINO
+    with pytest.raises(Invalid, match="Unsupported toolchain 'arduino' for RP2"):
+        validator(config)