Suppress spurious volatile and Python syntax warnings during builds (#9488)

esphome/platformio_api.py

@@ -78,6 +78,8 @@ def run_platformio_cli(*args, **kwargs) -> str | int:
     os.environ.setdefault(
         "PLATFORMIO_LIBDEPS_DIR", os.path.abspath(CORE.relative_piolibdeps_path())
     )
+    # Suppress Python syntax warnings from third-party scripts during compilation
+    os.environ.setdefault("PYTHONWARNINGS", "ignore::SyntaxWarning")
     cmd = ["platformio"] + list(args)
 
     if not CORE.verbose:

esphome/writer.py

@@ -162,6 +162,9 @@ def get_ini_content():
     # Sort to avoid changing build unflags order
     CORE.add_platformio_option("build_unflags", sorted(CORE.build_unflags))
 
+    # Add extra script for C++ flags
+    CORE.add_platformio_option("extra_scripts", ["pre:cxx_flags.py"])
+
     content = "[platformio]\n"
     content += f"description = ESPHome {__version__}\n"
 
@@ -222,6 +225,9 @@ def write_platformio_project():
         write_gitignore()
     write_platformio_ini(content)
 
+    # Write extra script for C++ specific flags
+    write_cxx_flags_script()
+
 
 DEFINES_H_FORMAT = ESPHOME_H_FORMAT = """\
 #pragma once
@@ -394,3 +400,16 @@ def write_gitignore():
     if not os.path.isfile(path):
         with open(file=path, mode="w", encoding="utf-8") as f:
             f.write(GITIGNORE_CONTENT)
+
+
+CXX_FLAGS_SCRIPT = """# Auto-generated ESPHome script for C++ specific compiler flags
+Import("env")
+
+# Add C++ specific warning flags
+env.Append(CXXFLAGS=["-Wno-volatile"])
+"""
+
+
+def write_cxx_flags_script() -> None:
+    path = CORE.relative_build_path("cxx_flags.py")
+    write_file_if_changed(path, CXX_FLAGS_SCRIPT)