Function _intercept_emcc_compile

ci/wasm_build.py:1069–1124

Run emcc compile with verbose output to capture clang command. Runs emcc normally but with EMCC_VERBOSE=1 and EM_FORCE_RESPONSE_FILES=0 so the full clang subprocess command is printed to stderr. We parse it and save a template for future fast compiles via _fast_compile(). Returns t

(
    emcc_args: list[str],
    wrapper_path: Path,
    object_path: Path,
    build_dir: Path,
)

def _intercept_emcc_compile(
    emcc_args: list[str],
    wrapper_path: Path,
    object_path: Path,
    build_dir: Path,
) -> int:
    """Run emcc compile with verbose output to capture clang command.

    Runs emcc normally but with EMCC_VERBOSE=1 and EM_FORCE_RESPONSE_FILES=0
    so the full clang subprocess command is printed to stderr. We parse it
    and save a template for future fast compiles via _fast_compile().

    Returns the emcc exit code.
    """
    from ci.wasm_tools import get_emcc

    emcc = get_emcc()

    env = os.environ.copy()
    env["EMCC_VERBOSE"] = "1"
    env["EM_FORCE_RESPONSE_FILES"] = "0"

    result = subprocess.run(
        [emcc] + emcc_args,
        cwd=str(PROJECT_ROOT),
        stderr=subprocess.PIPE,
        text=True,
        env=env,
    )

    if result.returncode != 0:
        if result.stderr:
            print(result.stderr, file=sys.stderr, end="")
        return result.returncode

    # Parse and cache the clang command for future fast compiles
    clang_cmd = _parse_clang_from_verbose(result.stderr)
    if clang_cmd is None:
        return 0  # compile succeeded, just can't cache

    wrapper_str = str(wrapper_path)
    object_str = str(object_path)
    template: list[str] = []
    for arg in clang_cmd:
        arg = arg.replace(wrapper_str, "{input_cpp}")
        arg = arg.replace(object_str, "{output_o}")
        template.append(arg)

    cache_file = build_dir / "clang_compile_args.json"
    cache_file.write_text(json.dumps(template), encoding="utf-8")

    # Save the key so _fast_compile can detect flag changes
    cache_key_file = build_dir / "clang_compile_args.key"
    cache_key_file.write_text(_compile_cache_key(emcc_args), encoding="utf-8")

    return 0