Function _intercept_emcc_link

ci/wasm_build.py:1266–1355

Run emcc link as subprocess with verbose output to capture wasm-ld command. Uses EMCC_VERBOSE=1 to make emcc print the wasm-ld command to stderr, then saves it (with placeholders) for future fast re-linking via _fast_link(). This is a one-time operation per build directory — subsequent

(
    emcc_args: list[str],
    sketch_object: Path,
    cached_wasm: Path,
    build_dir: Path,
    cwd: str,
    mode: str,
    library_archive: Path | None = None,
)

def _intercept_emcc_link(
    emcc_args: list[str],
    sketch_object: Path,
    cached_wasm: Path,
    build_dir: Path,
    cwd: str,
    mode: str,
    library_archive: Path | None = None,
) -> int:
    """Run emcc link as subprocess with verbose output to capture wasm-ld command.

    Uses EMCC_VERBOSE=1 to make emcc print the wasm-ld command to stderr,
    then saves it (with placeholders) for future fast re-linking via _fast_link().

    This is a one-time operation per build directory — subsequent links use
    _fast_link() which runs wasm-ld directly (~0.2s vs ~1.1s).
    """
    from ci.wasm_tools import get_emcc

    emcc = get_emcc()

    # Set up env to capture wasm-ld command and preserve temp files
    emcc_tmp = build_dir / "emcc_tmp"
    emcc_tmp.mkdir(parents=True, exist_ok=True)
    env = os.environ.copy()
    env["EMCC_VERBOSE"] = "1"
    env["EMCC_DEBUG"] = "1"  # preserves temp files (js_symbols stub)
    env["EMCC_TEMP_DIR"] = str(emcc_tmp)
    env["EM_FORCE_RESPONSE_FILES"] = "0"  # ensure full command, no @file

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

    if result.returncode != 0:
        # Print captured stderr so user sees the error
        if result.stderr:
            print(result.stderr, file=sys.stderr, end="")
        return result.returncode

    # Parse wasm-ld command from verbose output
    wasm_ld_cmd = _parse_wasm_ld_from_verbose(result.stderr)
    if wasm_ld_cmd is None:
        print("[WASM] Warning: could not capture wasm-ld command from verbose output")
        return 0  # link succeeded, just can't cache the fast path

    # Copy js_symbols stub from temp dir to build_dir for persistence
    emcc_temp_dir = emcc_tmp / "emscripten_temp"
    cached_stub = build_dir / "libemscripten_js_symbols.so"
    for i, arg in enumerate(wasm_ld_cmd):
        if "js_symbols" in arg:
            stub_src = Path(arg)
            if stub_src.exists():
                shutil.copy2(str(stub_src), str(cached_stub))