[core] Add support for extern "C" includes (#11422)

esphome/const.py

@@ -471,6 +471,7 @@ CONF_IMPORT_REACTIVE_ENERGY = "import_reactive_energy"
 CONF_INC_PIN = "inc_pin"
 CONF_INCLUDE_INTERNAL = "include_internal"
 CONF_INCLUDES = "includes"
+CONF_INCLUDES_C = "includes_c"
 CONF_INDEX = "index"
 CONF_INDOOR = "indoor"
 CONF_INFRARED = "infrared"

esphome/core/config.py

@@ -21,6 +21,7 @@ from esphome.const import (
     CONF_FRIENDLY_NAME,
     CONF_ID,
     CONF_INCLUDES,
+    CONF_INCLUDES_C,
     CONF_LIBRARIES,
     CONF_MIN_VERSION,
     CONF_NAME,
@@ -227,6 +228,7 @@ CONFIG_SCHEMA = cv.All(
                 }
             ),
             cv.Optional(CONF_INCLUDES, default=[]): cv.ensure_list(valid_include),
+            cv.Optional(CONF_INCLUDES_C, default=[]): cv.ensure_list(valid_include),
             cv.Optional(CONF_LIBRARIES, default=[]): cv.ensure_list(cv.string_strict),
             cv.Optional(CONF_NAME_ADD_MAC_SUFFIX, default=False): cv.boolean,
             cv.Optional(CONF_DEBUG_SCHEDULER, default=False): cv.boolean,
@@ -302,6 +304,17 @@ def _list_target_platforms():
     return target_platforms
 
 
+def _sort_includes_by_type(includes: list[str]) -> tuple[list[str], list[str]]:
+    system_includes = []
+    other_includes = []
+    for include in includes:
+        if include.startswith("<") and include.endswith(">"):
+            system_includes.append(include)
+        else:
+            other_includes.append(include)
+    return system_includes, other_includes
+
+
 def preload_core_config(config, result) -> str:
     with cv.prepend_path(CONF_ESPHOME):
         conf = PRELOAD_CONFIG_SCHEMA(config[CONF_ESPHOME])
@@ -339,7 +352,7 @@ def preload_core_config(config, result) -> str:
     return target_platforms[0]
 
 
-def include_file(path: Path, basename: Path):
+def include_file(path: Path, basename: Path, is_c_header: bool = False):
     parts = basename.parts
     dst = CORE.relative_src_path(*parts)
     copy_file_if_changed(path, dst)
@@ -347,7 +360,14 @@ def include_file(path: Path, basename: Path):
     ext = path.suffix
     if ext in [".h", ".hpp", ".tcc"]:
         # Header, add include statement
-        cg.add_global(cg.RawStatement(f'#include "{basename}"'))
+        if is_c_header:
+            # Wrap in extern "C" block for C headers
+            cg.add_global(
+                cg.RawStatement(f'extern "C" {{\n  #include "{basename}"\n}}')
+            )
+        else:
+            # Regular include
+            cg.add_global(cg.RawStatement(f'#include "{basename}"'))
 
 
 ARDUINO_GLUE_CODE = """\
@@ -377,7 +397,7 @@ async def add_arduino_global_workaround():
 
 
 @coroutine_with_priority(CoroPriority.FINAL)
-async def add_includes(includes: list[str]) -> None:
+async def add_includes(includes: list[str], is_c_header: bool = False) -> None:
     # Add includes at the very end, so that the included files can access global variables
     for include in includes:
         path = CORE.relative_config_path(include)
@@ -385,11 +405,11 @@ async def add_includes(includes: list[str]) -> None:
             # Directory, copy tree
             for p in walk_files(path):
                 basename = p.relative_to(path.parent)
-                include_file(p, basename)
+                include_file(p, basename, is_c_header)
         else:
             # Copy file
             basename = Path(path.name)
-            include_file(path, basename)
+            include_file(path, basename, is_c_header)
 
 
 @coroutine_with_priority(CoroPriority.FINAL)
@@ -494,19 +514,25 @@ async def to_code(config: ConfigType) -> None:
         CORE.add_job(add_arduino_global_workaround)
 
     if config[CONF_INCLUDES]:
-        # Get the <...> includes
-        system_includes = []
-        other_includes = []
-        for include in config[CONF_INCLUDES]:
-            if include.startswith("<") and include.endswith(">"):
-                system_includes.append(include)
-            else:
-                other_includes.append(include)
+        system_includes, other_includes = _sort_includes_by_type(config[CONF_INCLUDES])
         # <...> includes should be at the start
         for include in system_includes:
             cg.add_global(cg.RawStatement(f"#include {include}"), prepend=True)
         # Other includes should be at the end
-        CORE.add_job(add_includes, other_includes)
+        CORE.add_job(add_includes, other_includes, False)
+
+    if config[CONF_INCLUDES_C]:
+        system_includes, other_includes = _sort_includes_by_type(
+            config[CONF_INCLUDES_C]
+        )
+        # <...> includes should be at the start
+        for include in system_includes:
+            cg.add_global(
+                cg.RawStatement(f'extern "C" {{\n  #include {include}\n}}'),
+                prepend=True,
+            )
+        # Other includes should be at the end
+        CORE.add_job(add_includes, other_includes, True)
 
     if project_conf := config.get(CONF_PROJECT):
         cg.add_define("ESPHOME_PROJECT_NAME", project_conf[CONF_NAME])

tests/unit_tests/core/test_config.py

@@ -517,6 +517,35 @@ def test_include_file_cpp(tmp_path: Path, mock_copy_file_if_changed: Mock) -> No
         mock_cg.add_global.assert_not_called()
 
 
+def test_include_file_with_c_header(
+    tmp_path: Path, mock_copy_file_if_changed: Mock
+) -> None:
+    """Test include_file wraps header in extern C block when is_c_header is True."""
+    src_file = tmp_path / "c_library.h"
+    src_file.write_text("// C library header")
+
+    CORE.build_path = tmp_path / "build"
+
+    with patch("esphome.core.config.cg") as mock_cg:
+        # Mock RawStatement to capture the text
+        mock_raw_statement = MagicMock()
+        mock_raw_statement.text = ""
+
+        def raw_statement_side_effect(text):
+            mock_raw_statement.text = text
+            return mock_raw_statement
+
+        mock_cg.RawStatement.side_effect = raw_statement_side_effect
+
+        config.include_file(src_file, Path("c_library.h"), is_c_header=True)
+
+        mock_copy_file_if_changed.assert_called_once()
+        mock_cg.add_global.assert_called_once()
+        # Check that include statement is wrapped in extern "C" block
+        assert 'extern "C"' in mock_raw_statement.text
+        assert '#include "c_library.h"' in mock_raw_statement.text
+
+
 def test_get_usable_cpu_count() -> None:
     """Test get_usable_cpu_count returns CPU count."""
     count = config.get_usable_cpu_count()